Is It Good to Eat Sugar?

A few “Peat-atarians” – followers of the iconoclastic health writer Ray Peat – have accused us of being too skeptical of fructose. They think we should promote sugar consumption.

Here’s Travis Culp:

I think fructose is only conditionally problematic and that the consumption of it alongside glucose at a time of low liver glycogen is highly advantageous. In fact, I would go so far as to say that (somewhat slowly) drinking a can of soda upon waking (as disgusting as that is) would not result in any real glycation, insulin resistance, elevated TGs etc…. I think it’s beneficial to eat something really sugary upon waking …

Here’s Danny Roddy:

Peat has stated that … fructose … “powerfully” refills glycogen …

I would consider the ability to refill glycogen (minimizing adrenaline & cortisol release) to be an important factor in health …

It’s true that the ability to refill glycogen is essential for health; some genetic glycogen storage disorders are fatal in early childhood. But everyone who lacks a glycogen storage disorder has the ability to refill glycogen from multiple sources. In addition to fructose, glucose sugars and starches refill glycogen, as does milk sugar (a compound of glucose and galactose).

So the question is which combination of dietary sugars (a) is best at refilling glycogen and (b) makes the healthiest diet, all things considered?

Sugar Composition of the Diets

Both Danny and Travis framed their arguments as criticisms of our diet. They are really arguing that a Peat-style sugary diet is healthier than a PHD-style moderate-starch diet.

So before going further, let’s look at the sugar content of the diets we’re comparing.

First, note that PHD is not a zero-fructose diet. As an examination of the PHD Food Plate shows, PHD includes many fructose-containing plant foods – fruits, berries, and vegetables such as beets, onions, carrots, and squashes – plus “pleasure foods” like chocolate.

Also, PHD is not a zero-dairy diet, so for many practitioners it will include some milk sugars which are half galactose and half glucose.

In my diet personally, probably about 55% of carb calories come from starches, 30% from fruits, berries, and sugary vegetables, and 15% from dairy products such as yogurt. In terms of simple sugars, this translates to about 77% glucose, 15% fructose, and 8% galactose.

Not every Perfect Health Dieter will have the same sugar proportions; there is no obligation to consume dairy, and the relative proportions of starchy and sugary plants will vary according to taste. But let’s take mine as characteristic PHD proportions.

In a Peat-style diet, in contrast, the breakdown of sugars is near 50% glucose and 50% fructose.

So we aren’t comparing fructose against glucose, but a 77% glucose 15% fructose diet against a 50% glucose 50% fructose diet.

Why the Focus on Refilling Glycogen?

Why do the defenders of sugar focus on its ability to refill glycogen?

The reason is that fructose is treated by the body as a poison. Dietary fructose is shunted to the liver for disposal by conversion to glycogen, fat, lactate, or pyruvate.

Fructose is treated like a poison because it is dangerous. High doses of fructose have observable harmful effects even in short-term studies. Fructose does no good to the liver while it’s there, in fact fructose combined with polyunsaturated fats very effectively creates liver disease. Fructose in any other organ does harm; for instance, fructose promotes cancer growth.

Given fructose’s rapid disposal, any benefits from fructose have to be attributable to the glycogen or other products it is turned into. If fat, lactate, or pyruvate (a glucose product) provided benefits, dietary fats or starches would do the same, without the risk of fructose toxicity or fats getting stuck in the liver due to choline and methionine deficiency. So if fructose is to have benefits, it has to be via glycogen.

Here, then, is the challenge Peat-atarians face. Fructose has many proven harms. It has only one possible benefit: its ability to help re-fill liver glycogen. Peat-atarians have to show two things:

  1. That a diet with Peat-like sugar proportions – roughly 50% fructose, 50% glucose –is better than a diet with PHD-like sugar proportions – 15% fructose, 8% galactose, 77% glucose – at refilling liver glycogen.
  2. That better re-filling of liver glycogen improves the healthfulness of the diet.

How Do Sugars Perform at Refilling Glycogen?

Danny provides no citations for his claim that fructose “powerfully” refills glycogen. But Danny’s commenters help him out.

Daz, drawing upon a New York Times report, offers two studies [1] [2]. Cliff offers several more [3] [4]. Let’s see what these tell us.

The first study, “Fructose and galactose enhance postexercise human liver glycogen synthesis” [1], looks at athletes depleted of liver glycogen by intense cycling, and assessed the effectiveness of three sugar drinks at replenishing liver glycogen. The three drinks were:

  • 2/3 maltodextrin, 1/3 fructose;
  • 2/3 maltodextrin, 1/3 glucose;
  • 2/3 maltodextrin, 1/3 galactose.

Maltodextrin digests to glucose, so all three drinks are majority glucose. The athletes drink 275 calories of these drinks per hour for 6.5 hours after exercise. Galactose is non-toxic, but like fructose tends to be taken up by the liver.

Liver glycogen was measured every two hours with carbon-13 magnetic resonance imaging. Here were the results:

So 67% glucose / 33% galactose did the best, 67% glucose 33% fructose was close behind, and 100% glucose lagged.

Why does the 100% glucose drink underperform? One reason is that fructose and galactose, but not glucose, are preferentially targeted to the liver:

A factor of potentially larger magnitude in enhancing liver glycogen synthesis is the differential postabsorptive fates of fructose and glucose. Glucose is a relatively poor direct substrate for liver glycogen synthesis (24,27). Much of it is released from the liver into the systemic circulation to be stored as muscle glycogen (3,7). In contrast, fructose is primarily taken up by the liver … [1]

The second paper, “Superior endurance performance with ingestion of multiple transportable carbohydrates” [2], did not measure liver glycogen replenishment; instead, it gave its cyclists sugary drinks every 15 minutes throughout an intense 2-hr cycling test, and compared performance. Three different drinks were used: a 67% glucose 33% fructose drink, a 100% glucose drink, and a water-only control group. Performance was best with the 67% glucose 33% fructose drink, intermediate with the glucose drink, and worst with the water drink. The results suggest that the 67% glucose 33% fructose drink was better for liver glycogen replenishment, and that liver glycogen replenishment aided the cyclists’ performance.

The third paper, “Effect of different post-exercise sugar diets on the rate of muscle glycogen synthesis” [3], isn’t available to me electronically, so we’ll have to work from the abstract. It looked at muscle glycogen, measured using biopsies (ouch!), rather than liver glycogen.

It first assessed the effect of different amounts of glucose. It found that 0.7 g/kg body weight of glucose given every 2 hours would maximize the rate of muscle glycogen synthesis. For an 80 kg man, that works out to 56 g or 224 calories of glucose per two-hour period, or 112 calories per hour. Above this amount, the rate of muscle glycogen synthesis is unchanged.

It then compared three formulations at this same 0.7 g/kg body weight dose: 100% glucose, 100% sucrose (50% glucose, 50% fructose), and 100% fructose. Muscle glycogen synthesis rates were:

  • 5.8 mmol/kg/hr with 100% glucose
  • 6.2 mmol/kg/hr with 50% glucose, 50% fructose
  • 3.2 mmol/kg/hr with 100% fructose

If we fit a quadratic curve to these points, it predicts a peak rate of glycogen synthesis with 70% glucose, 30% fructose:

Athletes Agree: More Glucose Than Fructose

Of course, endurance athletes know that it’s beneficial to replenish glycogen during endurance events like marathons and triathlons.

Some authorities, including Tim Noakes, an exercise physiologist who has run over 70 marathons, believe that liver glycogen rather than muscle glycogen is the gating factor in marathon performance. From “The Science of Carbohydrate Loading” by David Peterson:

Remember also that muscle glycogen is committed to be used by muscle and cannot assist in maintaining blood sugar levels. Therefore should no additional carbohydrate be ingested during prolonged exercise, the task of maintaining blood glucose levels rests firmly on the liver’s glycogen stores and gluconeogenesis (the manufacturing of glucose from plasma amino acids). Oxidation of blood glucose at 70-80% VO2 max is about 1.0 g/min or about 60 g/hour. Therefore it can be predicted that even with full glycogen stores, a less conditioned athlete’s liver will be depleted of its carbohydrate within an hour and three quarters of continuous moderate intensity exercise. (Interestingly, the daily carbohydrate requirements of the brain and nervous system alone are enough to deplete the liver glycogen stores within 24 hours.) Once liver glycogen levels begin to drop and exercise continues the body becomes increasingly hypoglycemic (low blood sugar) mainly because blood glucose is depleted faster than it is replaced by gluconeogenesis. Professor Tim Noakes considers liver glycogen depletion and subsequent hypoglycemia to be the primary factors affecting fatigue and performance during extended duration races and especially in instances where muscle glycogen levels are low as well.

So marathoners and other endurance athletes will want to replenish liver glycogen as rapidly as possible during a race. What mix of sugars do they use?

The popular product is carbohydrate gels that can be swallowed at the same time water is taken. Here are the top carbohydrate gels sold on Amazon:

So the sugar mix ranges from 67% glucose to 100% glucose. No product uses 50% fructose.

Presumably, athletes have done a great deal of personal experimentation and know that these ratios do, indeed, optimize the speed of glycogen replenishment.

When athletes have no need for speed, as when they are carb loading before a marathon, then they eat starches like pasta and bread, not sugar. So to maximize total glycogen status, regardless of speed of filling, a carb mix close to 100% glucose works just fine.

Glycemic Control

The fourth paper, “Acute fructose administration decreases the glycemic response to an oral glucose tolerance test in normal adults” [4], is about how a bit of fructose affects the glycemic response to an oral glucose tolerance test.

It showed that a 9% fructose 91% glucose test (7.5 g fructose, 75 g glucose) produced a lower glucose area under the curve and higher insulin response than a 100% glucose test. Here’s the glucose response:

In general higher insulin and lower glucose is healthier than the reverse, so this is considered an improvement.

Summary of the Data

What these papers show is:

  • Glycogen replenishment proceeds the fastest with a mix of sugars consisting of about 70% glucose and 30% fructose or galactose.
  • Although this wasn’t tested, we can guess that a mix of fructose and galactose would be more effective than fructose alone, since it seems that utilizing multiple carbohydrate pathways is what drives the speedier glycogen replenishment. So the fastest glycogen replenishment might occur with something like 70% glucose 15% fructose 15% galactose.
  • Muscle glycogen replenishment is maximized with a carbohydrate intake of 100 calories per hour.
  • Athletes agree with the research, using carb gel packs that contain typically 30-40 g carbs with a composition of 67% to 100% glucose, 0% to 33% fructose.
  • Glycemic response to a large dose of carbohydrate may be improved by eating a 9% fructose 91% glucose mix.

From these data, I infer that for glycogen replenishment in liver or muscle, a PHD-style carb mix of 77% glucose, 15% fructose, 8% galactose is probably equal or superior to a Peat-style carb mix of 50% glucose, 50% fructose.


For athletes in the midst of a race, or in need of rapid recovery for a second race on the same day, speedy glycogen replenishment may be the endpoint to optimize. If so, they should eat a sugar drink composed of roughly 70% glucose and 30% fructose and galactose.

This is closer to PHD diet ratios than to Danny Roddy’s recommendation of orange juice or Travis Culp’s recommendation of soda!

But for others, speed of glycogen replenishment is hardly likely to be the parameter to optimize. There are unlikely to be significant benefits for non-athletes from replenishing glycogen 6.5% faster, as was found in the muscle glycogen study [3].

Speedier glycogen replenishment is almost the only known benefit to fructose consumption. It’s possible that low fructose doses, about 9% of carb calories (perhaps 2-3% of total calories), may improve glycemic control. This is a lower fructose fraction than is found in PHD, and far below the fructose fraction recommended by Danny and Travis.

Given the known risks of fructose consumption, especially with chronic intake at high doses or in conjunction with polyunsaturated fats, it seems prudent to err on the low side. It seems to me that the Peat-atarians have failed to provide any evidence at all in favor of a higher fructose intake than is provided by the fruits, berries, and sugary vegetables recommended by the Perfect Health Diet, save for athletes in the midst of a race or post-race recovery.


[1] Décombaz J et al. Fructose and galactose enhance postexercise human liver glycogen synthesis. Med Sci Sports Exerc. 2011 Oct;43(10):1964-71.

[2] Currell K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008 Feb;40(2):275-81.

[3] Blom PC et al. Effect of different post-exercise sugar diets on the rate of muscle glycogen synthesis. Med Sci Sports Exerc. 1987 Oct;19(5):491-6.

[4] Moore MC et al. Acute fructose administration decreases the glycemic response to an oral glucose tolerance test in normal adults. J Clin Endocrinol Metab. 2000 Dec;85(12):4515-9.

Leave a comment ?


  1. Zachariah Salazar


  2. Zachariah Salazar

    His basic plan would be meat fruit sugar coffee dairy and eggs AND COCONUT OIL. Sorry…

  3. @zachariah

    seems to me that dairy is such a lynchpin of peat’s advice that it makes me wonder if his ideas can succeed without it. do you have any thoughts on this?

  4. Zachariah Salazar

    If you read his articles about dairy and all of its qualities consuming dairy makes figuring out a healthy diet much easier. Why would you not want to eat dairy?


  5. @zachariah

    it’s not a matter of choice. myself, along with many other people are intolerant to many of the constituents in dairy. for me it’s the casein. so my original question still remains, do you think peat’s ideas can work in the absence of dairy?

  6. Zachariah Salazar

    Definitely you could do Peats method without dairy. Dr Peat looks at situations such as this as a sign to look for other things to repair in the diet. Ideally anything to improve cell function is worth paying attention to. Anything that the body cannot do is worth noting 🙂

    However I have been in this field for 23 years. I’ve never met a person that once the rest of their issues were covered, couldnt enjoy dairy. One of my missions in life is to seek out those that cannot tolerate dairy and help them enjoy ice cream.

    Wanna share? What is your issue w casein?


  7. zACHARIAH, how does peat explain the improved health from people eating salmon and other long chain omega 3’s? reducing their inflammation etc.

    how does peat explain the existence of something like nuts if they are so harmful but contain vitamin E, magnesium etc…?

    and lastly…about 90 % of the people i see adopt a peat-style gain lotsa weight. if his diet is so great at fixing gut and reduciing inflammation and regulating metabolism why hasnt he written a book, or better yet why havent people become more widespread in ‘peatism’?

    • Regarding nuts and seeds. The Vitamin E is their to prevent peroxidation of the PUFA’s. Oxygen damages seeds and humans’ cells membranes – duh… Vit E – an anti-oxidant, ‘sacrifices itself’ to prevent cell damage. Thus avoid PUFA’s – which are ubiquitous. Like less than 5% of total calories of the total fat. Next – fish oil is anti-inflammatory, which is synonymous with immunospressive. Short term decrease of inflammation ameliorates symptoms via immunosupression – but long term is another story. Fish oil is not used in animal studies by learned biochemists due to the auto-oxidation, duh… because it is unstable, a PUFA.

      Peat actually doesn’t have a diet, he talks about strategies to optimize a cell’s respiration. People who try to make it a diet often butcher themselves by taking things to a place they do not understand.

  8. @Malory

    Not going to speak for Peat, since I’m not familiar with his work beyond what I read on Danny’s blog, but speaking from my own understanding of the subject:

    “how does peat explain the improved health from people eating salmon and other long chain omega 3?s? reducing their inflammation etc.”

    Ratio between n6:n3 fats matters because they share a lot of transport proteins and receptors and stuff. Doesn’t mean that less of both won’t be better in the long term.

    “how does peat explain the existence of something like nuts if they are so harmful but contain vitamin E, magnesium etc…?”

    There’s no reason to believe that humans or our ancestry played a significant role in the evolution of nuts. Many animals eat nuts.

    “about 90 % of the people i see adopt a peat-style gain lotsa weight. if his diet is so great at fixing gut and reduciing inflammation and regulating metabolism why hasnt he written a book, or better yet why havent people become more widespread in ‘peatism’?”

    Can’t confirm or deny those numbers, but sugar is clearly a very highly rewarding food, and when pairing it with other rewarding foods it could cause overconsumption without the compensatory upregulation of metabolism to burn off the excess calories. That said, for lean individuals with proper leptin signaling like myself and Danny Roddy, copious amounts of sugar do not seem to cause weight gain, and in fact in many instances have caused weight loss as a result of the improved body temperature and sleep.

  9. zachariah, my casein intolerance symptoms are increased sinus congestion, constipation, headache & depression. lactose gives me bloating.

  10. Zachariah, thx for all your Peat info.

    I have read that Peat suggests trying (supplementing) Ice Cream before bed, if you have issues with sleep (to reduce stress i think?).
    I like the idea of this.

    If the ice cream does not help or just to mix things up; Do you know if he suggests any other pre-bed/evening ‘snacks’ to help with sleep?

  11. 02/07/12 – Triplet Tuesday - pingback on February 6, 2012 at 9:01 pm
  12. Peats ideas are intruiging, but one thing that still bothers me about massive dairy consumption is the possible correlational liks between high casein intake and increased occurence of cancer that Colin Campbell observed. I know most of Campbell’s study was hogwash, but in reading Paul J’s and Denise Minger’s breakdown of it it seems the casein-cancer link could still be somewhat valid.

    Does Peat have any opinions on this concern?

  13. Just a very minor point. I have one long run per week (minimum of 10 miles and as long as 15). It is the only time I take energy gel packs. I don’t use them when I do speed work. I am 52 years old, in good shape with low body fat.

    I used two of the brands that were referenced in one of the studies you highlighted. For a long time I used the Cliff gels. While not a great reason, I used them because I liked two of the flavors quite a bit, chocolate and mocha. They seemed to perform pretty well for me. I definitely noticed that it was better than just taking in water. Well, when I ran out, the local store I buy them from was out, so I ended up using a Power Bar gel formulation. Well, sadly, it isn’t nearly as tasty and has a consistency I don’t like as much (much more liquid). BUT, there is absolutely no question it performed better. When I finish my long runs, there is always a level of discomfort in the last little bit. However, it was considerably less with the Power gel formulation. Well, having the last several miles made easier is a lot more important to me than the taste so Power Bar gels it is with the the 67% glucose and 33% fructose formulation for me.

    I know anecdotal evidence isn’t usually worth a hill of beans, but I thought I would pass it on since I happened to have used two of the gels you referenced in that study.

  14. Thanks, Mario. It’s always nice when personal experience confirms published research. I would expect the Power Bar gels would perform better than sugar water (50% fructose 50% glucose) as well.

  15. I am not sure if any of you are familiar with the writings of Lyle McDonald – his target demographic appears to be under 40, overwhelmingly male and bodybuilders/athletes – but there is a poster on his forum, well respected guy – who trains athletes in Europe.

    I recognize this is anecdotal as well, but the guy reports that he trains both men and women, but has noticed that some of the women he trains don’t see progress in body recomposition until they add fruit to their diets – and specifically, only fruit. Once the fruit is added, fat loss resumes and lean gains are noted.

    I would like to add my voice to the chorus. I am a middle aged woman who also hopes to find respected advice on the issues we face. I have searched for someone writing to our demographic, but coming up empty and others such as Lyle, note we have different issues – but as of yet, no one is focusing on them.

    Thanks, Lynn

  16. George Henderson

    I disagree that galactose is non-toxic; it is probably more toxic than fructose, which is why it also jumps the queue. 100mg/Kg long term will destroy nerves in mice, which is a lot less than the amount of fructose it takes to cause fatty liver.
    Impaired liver function decreases galactose clearance. And galactose is highly mucagenic in some people, especially when cold or flu virus is present.

    I think there is a high but unknown % of galactose sensitivity in the population, and this is may be more important than fructose in contributing to metabolic syndrome.
    Lactase deficiency exists for a reason – to decrease galactose exposure of many sensitive individuals.

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  19. George Henderson

    “I think there is a high but unknown % of galactose sensitivity in the population, and this is may be more important than fructose in contributing to metabolic syndrome.
    I meant, in these individuals.
    There is a dietician with a succesful weightloss programme in NZ (saw on TV, can’t find on Google) who gets good results with dairy avoidance. This would make sense if her patients were galactose sensitive (or maybe reduced fat milk is becoming a major carb source for health-conscious women, and milk solids are added to many ersatz foods, so it’s good to avoid for other reasons).

  20. Zachariah Salazar


    “….zACHARIAH, how does peat explain the improved health from people eating salmon and other long chain omega 3?s? reducing their inflammation etc.”

    They are immuno suppressive. Not all things that quell inflammation are good.

    “….how does peat explain the existence of something like nuts if they are so harmful but contain vitamin E, magnesium etc…?”

    Um birds need food too? There are many things that exist that have both nutritious ingredients AND poisons at the same time…

    “…..and lastly…about 90 % of the people i see adopt a peat-style gain lotsa weight.”

    Yep. When people have sluggish metabolisms from eating things like grains and PUFAs and then you return to an energy intake that you SHOULD be able to handle you will gain weight until you drive your metabolism back up. On of the reasons that Peat is so interested in repairing thyroid function is that with food alone it can take 2-3 years to repair metabolism; with thyroid this time can be reduced to weeks or months.

    Another reason is that people are terrible about following an RP style of eating. They read they can have ice cream and OJ and leap in without understanding often waiting weeks to dig deeper….

    “….if his diet is so great at fixing gut and reducing inflammation and regulating metabolism why hasnt he written a book, or better yet why havent people become more widespread in ‘peatism’?”

    He has written several books on HEALTH and has a running newsletter. Just not a diet book. He’s a practitioner; he assess patients and adjusts based on data. Hard to do in a book. See explanation in my first post.

  21. Zachariah Salazar


    Unfortunately its not that simple. The stress reduction has to do with sugar and low blood glucose during sleep. So ice cream can be a simple step but it may involve salt, protein etc many things.

    “Increasing the bodys energy level and temperature improves the quality of sleep.” R Peat

    Go to his website and type sleep into the search engine. Its a much easier start!

  22. Zachariah Salazar

    Rob White:

    If you go to his site you’ll see a dearth of info regarding cellular respiration, cancer, dairy and calcium.

    That will give you a better view of why dairy is so important (beyond simple explanations like lots of calcium but low phosphorus and casein is ANTI inflammatory)…

  23. 12.07.11 | Phenomenal CrossFit - pingback on July 10, 2012 at 7:14 pm

    As for th omega 3 question, X-rays also reduce inflammation of arthritis etc. Like Omega 3, they suppress the immune system. Not really healthy though dont you agree?

  25. The effect of X-rays on pain is probably hormetic. It appears to happen quickly, which would not be the case with immunosuppression. And as far as I know it is a rare event. Also, the dose of radiation from one X-ray is unlikely to be sufficient to depress immunity. Omega-3s have many modes of action and can only be characterized as immunosuppressive at high doses, or when they lower cholesterol to unsafe levels.

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  28. This is an old article, but I’d like to make a few comments that I think are important.

    I was one of those whose diet was thrown into temporary disarray by the rising popularity of Peat’s ideas. I was willing to easily accept most of his opinions (the toxicity of PUFAs, the benefits of saturated fat and coconut oil, the importance of getting enough carbohydrate, the importance of thyroid and metabolism, the importance of the intestine, even the idea that higher levels of calcium intake may be beneficial). But his assertion that starch was harmful, and should thus be replaced with sugar, didn’t make any sense in light of the very sound information presented here and elsewhere on the Internet. Plus, I could not find an example of Peat or any of his disciples explaining in coherent detail exactly why starch was supposedly bad for you, and why fructose was superior to glucose. So I decided to learn as much as possible about these carbohydrate sources so that I could come to some informed conclusions.

    Here’s what I realized: Peat’s terminology is very misleading. He talks about “sugar” being absolutely vital to so many important physiological processes, but never actually specifies WHICH sugar he is referring to. I assume now that he is talking about glucose, which is the only sugar that has any really vitally important biological roles. But when I hear the word “sugar,” I think of table sugar, which is equal parts glucose and fructose.

    The evidence for fructose having any important biological roles is pretty thin, especially considering that it is rarely even allowed to enter the circulation under normal circumstances. Peat seems to believe that fructose has uniquely beneficial properties, but the only “benefits” of fructose that make any sense to me are that it can indirectly support blood glucose levels via its conversion into liver glycogen, and that it can support T3 production in the liver by the same mechanism (keeping the liver relatively saturated with glycogen). But glucose in sufficient quantities can also replenish liver glycogen, as Paul has pointed out. So fructose is probably not necessary at all.

    Even if Peat believes fructose has magical powers, he MUST acknowledge that glucose is essential and is capable of performing all of the roles he considers important: stimulating oxidative metabolism, replenishing liver glycogen, suppressing free fatty acids and stress hormones, etc. So we’re left wondering why he deprecates starch.

    Starch itself is a polysaccharide consisting of amylose and amylopectin, long chains of glucose molecules that can be easily hydrolyzed by amylase enzymes into glucose sugars, and then safely, cleanly, efficiently transported into the bloodstream. So Peat’s idea that “starch” is somehow harmful is really bizarre, and it directly contradicts a lot of his other ideas.

    I think it comes down to two things: one, Peat believes the higher glycemic index of starch makes it inferior to sucrose and fructose. But as Paul has explained, consuming starch with saturated fat in the context of a normal meal attenuates its glycemic impact, so that argument doesn’t hold much water.

    Two, I think Peat may be confusing or conflating starch itself (i.e. amylose and amylopectin) with the many indigestible carbohydrates found in starchy plants like beans and grains, such as fructans and galactans (member of the FODMAPs family). Humans lack the enzymes to digest these carbohydrates, so it’s very natural that they would cause problems in a lot of people. As far as I know, white rice and tubers contain little to no FODMAPs, so that shouldn’t be a problem.

    To add to the confusion, Peat often says that white rice and potatoes are healthy, “except for their starch.” WTF? I think Peat is either confusing starch itself with indigestible plant compounds or simply has some bizarre opinions about the benefits of fructose and the relevance of the glycemic index of starch.

    Either way, I can see no good reason NOT to get the vast majority of my daily carbs from clean starches like potatoes and rice, and keep sugar to a minimum. Peat and his proponents have yet to convince me otherwise.

    • Hi Brendan,

      You’ve given a good summary of the issues, but Peat seems to have one other argument against starch: he believes that starch granules enter the body through “persorption” and can block blood vessels or cause other problems.

      See eg

      These ideas derive from a G. Volkheimer. His primary papers are and and and and

      As far as I am aware, nobody but Peat today believes that persorption of starch granules is a major factor in health.

      • and of course, this does not mean peat is wrong. i enjoy your objectivity paul, and the fact that you seem to enjoy pouring over research and attempting to help people. i am much more of an applier of ideas, a self-experimenter – by dire necessity, of course.
        i went through PHD on my way to peat, and then eventually passed through peat to where i am now. ultimately i think where everyone has to go is into their own undiscovered country, because no amount of rat or human studies is going to tell them about their own selves.
        there’s that old native american saying, all it takes is one white crow to prove that not all crows are black…

      • Thanks, Paul. I do remember seeing that idea articulated somewhere, but I didn’t pay much attention to it, probably because I’ve never seen it proposed anywhere else.

        Given my experiences with sugar and fruit (neither one is very kind to me), it’s a theoretical risk I’m willing to take.

      • I researched this awhile back and thought I would share my notes, in case this actually were to concern anybody…

        Volkheimer used 200g of potato starch to cause embolisms in his subjects. Think about that for a moment. That’s an incredibly large dose of starch granules. Even people who eat raw potato starch—for the resistant starch—rarely consume more than 40-50g per day. On the PHD, it would be a challenge to eat more than 8-12g of starch granules in a day from food.

        Volkheimer believed that persorption was some kind of flaw in the gut that allowed starch granules to leak through. And if starch granules that were larger than a red blood cell (6-8 microns in diameter) could get stuck in the blood vessels and cause blockages and embolisms. However, it’s highly unlikely that the lymph and blood vessels are not prepared to handle such intrusions—for instance, it’s well recognized that the liver is specifically designed to filter such particles from the blood.

        If we are going to worry about starch granules—which are often larger than the diameter of a red blood cell—then we must also worry about anything else that fits this criteria:

        Activated charcoal, has a particle size range of 1-150 microns, and seems to have the ability to detoxify the blood.

        Carrots have a starch granule size of 4-26 microns.

        Raw unfiltered honey, contains pollen that range from 2.5 to 1,000 microns. Most honey producers will filter the pollen out their honey with sieves that range from 50 microns (heavily filtered) to 600 microns (lightly filtered). But, as we know, Hunter Gatherer populations tend to eat a lot of honey and they didn’t filter their honey with modern sieves. So, I can imagine lots of large and small pollen getting persorbed by Hunter Gatherers every day.

        Once I realized that, if occurred to me that it persorption probably wasn’t a design flaw in our bodies. Combine that with the practice of geophagy (eating dirts and clays) and you get the picture that these particles are probably supposed to temporarily roam through our blood vessels. Persorption appears to be an intentional mechanism with a purpose.

        Raw meat is rich in glycans (glycolipids, glycoproteins, etc.), which is what we know of as animal fiber. Animal fiber is persorbed as well, and likely has a very wide range. Some of these glycans are probably used throughout the body. In fact, any fiber particle that is eaten from any food will surely become persorbed in the same manner.

        Glycosaminoglycans (GAGs) from blueberries literally get transported to your blood vessels and play a role in maintaining their health. Without persorption, there would be no way for GAGs to contribute to the health of blood vessels.

        Beta-glucans (usually acquired from mushrooms), which are are considered to be “keys” that turn on the body’s macrophage defense (immune) system. David Wolfe describes how they work, like this:

        David Wolfe said: “Specifically, here is how it works: the beta glucans found in [mushrooms], other herbs, foods, or supplements enter the body via the small intestine and are captured by the macrophages. To be activated by beta glucans, the macrophages must first “ingest” the beta glucans through specific beta glucan receptor sites on these cells’ membranes. Then the macrophages internalize and fragment the beta glucans within themselves and transport these fragments to the bone marrow (helping stimulate more stem cells) and to the reticuloendothelial system (RES). The beta glucans fragments are eventually released by the macrophages and taken up by other immune cells, including neutrophils , monocytes, natural killer cells, and dendritic cells, leading to numerous enhanced immune responses, 19 including adaptability against and deactivation of foreign pathogens, genotoxicity (toxins harmful to genetics), cancerous growth formations, and environmental toxicity.

        According to a study that appeared in the Journal of Hematology and Oconology in 2009, “animals pretreated with purified glucan particles are subsequently more resistant to bacterial, viral, fungal, and protozoan challenge, reject antigenically incompatible grafts more rapidly and produce higher titers of serum antibodies to specific antigens.”

        SOURCE: Wolfe, David (2012-09-11). Chaga: King of the Medicinal Mushrooms. North Atlantic Books.

        When you put it all together, you can sort of see the big picture of what the body does with persorption. It selectively persorbs particles, perhaps based on their size, so that these particles can get exposed to the entire body and the immune system in a matter of minutes. And then the unneeded particles disappear — often filtered out by the liver or lymphatic system.

        I suspect as long as you are eating quantities of particles that are within the range of normal human consumption, you are fine. The amount of RS that most people consume (5g to 40g) is within the normal limits that would have been eaten by Andean indians or even Asians consuming Dioscorea opposita (a tuber high in resistant starch granules). I don’t see how that could be especially problematic within the context of the naturally occurring persorption that we have always been exposed to.

        The concern with persorption, if there is one, is likely from man made particles that the body may not be prepared to filter.

        • Thanks Duck. Well researched and presented. I believe you are right. Great comment!

        • Superb comment indeed. Thanks; I like especially you kept track of diameter size of particles and capillaries. Even RBC’s squeeze and deform to pass through capillaries. This is a problem when zeta potential of blood (colloidal/electrical property of blood). So you are right, we may need to “worry about anything else that fits this criteria.”

  29. Rice vs. Sugar | Mark's Daily Apple Health and Fitness Forum page - pingback on November 8, 2012 at 9:42 pm
  30. Per Paul’s theory, “Presumably, athletes have done a great deal of personal experimentation and know that these ratios do, indeed, optimize the speed of glycogen replenishment.

    When athletes have no need for speed, as when they are carb loading before a marathon, then they eat starches like pasta and bread, not sugar. So to maximize total glycogen status, regardless of speed of filling, a carb mix close to 100% glucose works just fine.”

    I’d take issue with this – I am a reasonably geeked-out athlete and my handle on which gels/drinks have which ratio of carbs is still not in my arsenal. Most folks buy what sounds tasty and is on sale with no inkling of the formulas or why they might actually work.

    And they eat pasta because it is the conventional wisdom, not because they’ve done an N=1 test to see if it actually works.

    That’s my experience, anyway – that most folks know as little as possible in order to live their lives.

  31. Does anyone have any information about coconut sugar? Whether that is a safe/healthy sugar?


  32. This is about the best article I’ve ever read about sugar, especially as it applies to both regular and athletic folks. Thank you, Paul!

  33. This article states that brown rice syrup is nearly 100% glucose, but Wikipedia states that it is 45% maltose, 3% glucose, and 52% maltotriose. I know Wikipedia isn’t always the most reliable source, so I looked around and found this same breakdown on a few other sites as well. Just wondering if anyone has looked into this since the purported health benefit of brown rice syrup is due to the high glucose content as opposed to other sugars.

  34. You are completely wrong about Ray Peat’s diet.

    He doesn’t say that you have to eat all your carbohydrates from sucrose. As a guideline he suggests to consume 2l of milk and 1l of orange juice. I have done the numbers and this is: 50% glucose, 23% fructose and 27% galactose.

    For more information about the Ray’s point o view about sugar:

  35. Have I missed something here…?
    You mention that Peat eaters get 50% glucose, 50% fructose and that this is inferior to PHD way which typically is 77% glucose, 15% fructose, 8% galactose..
    Pardon me if this is already covered, as I have not as yet read all the comments but I eat a Peat sort of diet and drink ~4 pints of milk a day along with ripe fruits ; starches I eat will be white rice 2-3 times a week, and oatmeal/ porridge several times a week.
    My point being that 4 pints of milk is quite a lot of galactose too, what ?

  36. The main issue with this is that you’re defending your income.

    Your livelihood depends on the “PHD”, when money comes into the equation, it’s almost impossible to remain impartial and search for the correct answer, instead you fight to maintain your (and your family’s) financial health, which is completely bound with PHD being “correct”.

    Same goes for Mark Sisson and Primal.

    • Nonsense. Like saying firemen can’t fight fires because their livelihood depends on fires. In fact my income from PHD depends far more on providing correct answers, than on sticking to past answers. And PHD is not my sole income. Nor does that income matter more to me than truth and integrity. So you’re wrong on multiple counts.

      • actually not so much nonsense Paul – firemen HAVE been known to START fires they then participate in fighting…. that aside it is fine for Smith to be skeptical, but it is not a useful stance to convince others if he then does not comment on the the Perfect Health Diet itself. Skeptics lack credibility as their stance is from fear and lack of knowledge. In the end everyones’ income is dependent on the need their service fulfils. In this case it seems that the PHD has a following that is not merely based on clever talking but on genuine results for those who have actually used it.

      • I suspect that very few of us start at the PHD. We all start somewhere else, and when even Keto fails us we start digging deeper for answers. In my case its Hashimotos that even Zero carb can’t shift weight from.

        By the time we find the PHD, most of us could do a degree in nutrition without ever opening a textbook 🙂 So what matters most to us is hard science; which is what you provide.

        I’m here currently researching whether to follow your approach, or Peat’s. I don’t necessarily believe they are mutually exclusive, and in then end we are all N=1 experimenters anyway. I suspect in my case FODMAPS are an issue, and I almost certainly need to do a leptin reset.

        So yes – the PHD to me is about providing correct, science-based answers and I find your blog extremely useful for that reason.

        Keep up the good work !!

  37. Perhaps I am misunderstanding or oversimplifying something, but in my understanding, isn’t the benefit of 50/50 fructose/glucose carbohydrate source that it preferentially fills liver glycogen, provided there is not more ingested than can be converted to glycogen in the liver (and therefore would have to be converted to fat to avoid toxicity)? The benefit wouldn’t simply be to athletes looking for speed refilling, but anyone who wants to top-off liver glycogen for mood, thyroid, etc while daily muscle activity is still fueled primarily by fat. In addition, any negative effects caused by the insulin spike from consuming carbs is blunted by the fructose. In order to fill liver glycogen with glucose, a significant amount of muscle glycogen must be replenished first, resulting in less fat burning. This wouldn’t mandate the massive carb consumption of some adherents to Peat’s work, but it would perhaps suggest benefit to moderate fruit consumption (up to about 5 servings a day, assuming the liver can store ~500 calories worth of glycogen), in place of, or with small amounts (~40g) of starch?

    I’d appreciate if anyone could poke holes in this idea or otherwise comment. I’m only superficially familiar with Peat’s work, but discovered PHD after VLC-style paleo revealed its limited shelf-life.

  38. It should be noted that Clif Shot Gels no longer contain brown rice syrup — they’re now using a maltodextrin/sugar combination.

  39. Oh, and by the way, Ray Peat gives out very risky advice IMHO, gobbled up mainly by very young people who typically can get away with eating all sorts of sugary crap.

    My health has gone downhill markedly since trying his ‘advice’ and that of Matt Stone, who also has this ‘oh, you can eat anything/go by your cravings’ advice.

    • You are one of these people Kelly, like I said….”People who try to make it a diet often butcher themselves by taking things to a place they do not understand.”

      The main reason to conceive glycogen depletion is to achieve a concrete sense that muscles and liver store glycogen – and in turn – you may quantify carb intake according to a metric – and NOT by taste. Personally, I think 5-year old need to learn this, since depletion/repletion is easily visualized as emptying and filling a cup.

      As an exercise physiologist I appreciate Peat’s sense of history and insight into the mechanisms of cellular respiration. You are definitely confused if you thought I followed his ‘diet’ – and I already made clear my thoughts on people who try to follow his ‘diet’. They botch things. Sorry to hear you followed Peat or Matt Stone. btw… You have no clue how I feed myself or what I ‘follow’.

      • Ed, I have no idea why you thought I was responding personally to you. I was just posting an update about the Clif Shots ingredients, then added my comment about Peat and Stone.

        It had nothing to do with you, and as a result, of course I ‘have no clue’, nor am I interested in what you feed yourself or what you follow.

  40. Re in A recent tv program aired on ABC (Australia) nov 2014 – fat not fiction, Noakes was interviewed as completely recanting his former recommendations re sugar/ carb diet especially for athletes , including saying he was wrong!. He is currently advising higher fat diet as it provides continuous energy without the highs and lows and harmful effects associated with raised insulin/ glucose levels. Unfortunately his previous views / books will continue to be used by those who have not kept up to date with new information…

    • Noakes is getting a lot of flack these days, for recommending banting (low carb, high fat) for babies. It seems that a lot of people think that babies will die if they are not fed lots of cereals, refined starches and sugars. If this view were true, then baby eskimos are actually zombies, and masai babies probably must be sneaking behind the bushes to eat some cookies while mommy sleeps.

      I agree with Paul Jaminet in that we need some carbs for thyroid function and to form some mucus to prevent the stomach to digest itself. Probably, some humans need more carbs than others. But if we, as newborns, needed mostly sugars, then human milk will have mostly sugars. Yet, it has mostly fat and proteins. What mammal produces milk with very low fat and very high CHO content?

      This is crazy.

      • Human breast milk is 39% carb, 54% fat. So it looks like babies need both carbs and fat, but very little protein. If Noakes is suggesting deviating from breast milk for babies, he deserves some flak.

        • Just for that sake of clarity Paul,
          for anyone reading,
          are those %s by energy or weight.

          (i may beat you to the answer when I check the book later)

        • I think he suggests deviating from porridge. Especially, low fat, iron-filings loaded, gmo corn and gmo soy based porridge.

          He says babies should be breast feeding for two whole years. And some experts still think that is too much. And there is still people out there that say that eggs have too much cholesterol for three-year-olds.

          Regarding proteins, if you say that human breast milk has very little protein, some innocent bystander may misunderstand that. It is not that HBM has very little protein, meaning babies barely need any protein. Probably, it is the right amount of protein, for that stage of life. And it happens to be a very small amount compared to fat and carbs. And water, which babies also need, as much as breathing air, or some sun exposure, or sleeping.

          I don’t know of anyone who would try to defend a low-carb low-fat high-protein diet for anyone. My understanding, and please correct me if I’m worng, is that excess proteins are either not absorbed or transformed in other things, as energy substrate. So, unless one does not eat for a long time, or chooses to only eat twigs, it is difficult to not have enough proteins. At any age, if there is plenty of food, any malnourishment should be attributed to malabsorption.

      • ” But if we, as newborns, needed mostly sugars, then human milk will have mostly sugars. Yet, it has mostly fat and proteins.” quote by byrd.

        So if we refer to Paul’s info on human breast milk,
        human breast milk is indeed mostly carbs*…*By Weight

  41. Is there any difference between consuming, say, 400 calories of pure glucose (dextrose) vs. 400 calories of a starch that breaks down into 100% glucose, e.g. white rice?

  42. Link for the paper Effect of different post-exercise sugar diets on the rate of muscle glycogen synthesis.

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