Dangers of Zero-Carb Diets, IV: Kidney Stones

Kidney stones are a frequent occurrence on the ketogenic diet for epilepsy. [1, 2, 3] About 1 in 20 children on the ketogenic diet develop kidney stones per year, compared with one in several thousand among the general population. [4] On children who follow the ketogenic diet for six years, the incidence of kidney stones is about 25% [5].

A 100-fold odds ratio is hardly ever seen in medicine. There must be some fundamental cause of kidney stones that is dramatically promoted by clinical ketogenic diets.

Just over half of ketogenic diet kidney stones are composed of uric acid and just under half of calcium oxalate mixed with calcium phosphate or uric acid. Among the general public, about 85% of stones are calcium oxalate mixes and about 10% are uric acid.  So, roughly speaking, uric acid kidney stones are 500-fold more frequent on the ketogenic diet and calcium oxalate stones are 50-fold more frequent.

Causes are Poorly Understood

In the nephrology literature, kidney stones are a rather mysterious condition.

Wikipedia has a summary of the reasons offered in the literature for high stone formation on the ketogenic diet [4]:

Kidney stone formation (nephrolithiasis) is associated with the diet for four reasons:

  • Excess calcium in the urine (hypercalciuria) occurs due to increased bone demineralisation with acidosis. Bones are mainly composed of calcium phosphate. The phosphate reacts with the acid, and the calcium is excreted by the kidneys.
  • Hypocitraturia: the urine has an abnormally low concentration of citrate, which normally helps to dissolve free calcium.
  • The urine has a low pH, which stops uric acid from dissolving, leading to crystals that act as a nidus for calcium stone formation.
  • Many institutions traditionally restricted the water intake of patients on the diet to 80% of normal daily needs; this practice is no longer encouraged.

These are not satisfying explanations. The last three factors focus on the solubility of uric acid or calcium in the urine; the first on availability of calcium, one of the most abundant minerals in the body.

There is no consideration of the sources of uric acid, oxalate, or calcium phosphate.

Two of the factors focus on urine acidity, but alkalinizing diets have only a modest effect on stone formation. In the Health Professionals Study and Nurses Health Study I and II, covering about 240,000 health professionals, people with the lowest scores for a DASH-style diet (an alkalinizing diet high in fruits, vegetables, nuts, and legumes) had a kidney stone risk less than double that of those with the highest DASH-style scores. [6]

On ketogenic diets specifically, supplementation with potassium citrate to alkalinize the urine and provide citrate reduced the stone formation rate by a factor of 3. [3] They were still more than 30-fold more frequent than in the general population.

It seems the medical community is still unaware of some primary causes of stone formation.

Uric Acid Production

One difference between a ketogenic (or zero-carb) diet and a normal diet is the high rate of protein metabolism. If both glucose and ketones are generated from protein, then over 150 g protein per day is consumed in gluconeogenesis and ketogenesis. This releases a substantial amount of nitrogen. While urea is the main pathway for nitrogen disposal, uric acid is the excretion pathway for 1% to 3% of nitrogen. [7]

This suggests that ketogenic dieters produce an extra 1 to 3 g/day uric acid from protein metabolism. A normal person excretes about 0.6 g/day. [8]

In addition to kidney stones, excess uric acid production may lead to gout. Some Atkins and low-carb Paleo dieters have contracted gout.

Oxalate Production

Our last post (on scurvy) argued that very low-carb dieters are probably inefficient at recycling vitamin C from its oxidized form, dehydroascorbic acid or DHAA.

If DHAA is not getting recycled into vitamin C, then it is being degraded. Here is its degradation pathway:

The degradation of vitamin C in mammals is initiated by the hydrolysis of dehydroascorbate to 2,3-diketo-l-gulonate, which is spontaneously degraded to oxalate, CO(2) and l-erythrulose. [9]

Oxalate is a waste material that has to be excreted in the kidneys. Vitamin C degradation is a major – in infections, probably the largest – source of oxalate in the kidneys:

Blood oxalate derives from diet, degradation of ascorbate, and production by the liver and erythrocytes. [10]

Since the loss rate from vitamin C degradation can reach 100 g/day in severe infections, and most of that mass is excreted as oxalate, it is apparent that a very low-carb dieter who has active infections, as did I and KM in the scurvy post, or some other oxidizing stress such as injury or cancer, may easily excrete grams of oxalate per day, with the amount limited by vitamin C intake.

Dehydration and Loss of Electrolytes

Excretion of oxalate consumes both electrolytes, primarily salt, and water:

In mammals, oxalate is a terminal metabolite that must be excreted or sequestered. The kidneys are the primary route of excretion and the site of oxalate’s only known function. Oxalate stimulates the uptake of chloride, water, and sodium by the proximal tubule through the exchange of oxalate for sulfate or chloride via the solute carrier SLC26A6. [10]

Salt and water are also needed by the kidneys to excrete urea and uric acid.

Personally, I found that my salt needs increased dramatically on a zero-carb diet. I needed at least a teaspoon per day of salt when zero-carbing, compared to less than a quarter-teaspoon when eating carbs.

As a result of loss of salt and water, low-carb dieters tend to become dehydrated. This is also a widely-observed side effect on ketogenic diets.

We’ve all seen what happens to urine when we’re dehydrated: it becomes colorful due to high concentrations of dissolved compounds.

As urine becomes saturated, it no longer possible for uric acid and oxalate to dissolve. They precipitate out and initial deposits nucleate further deposits to form kidney stones.

Polyunsaturated Fats and Kidney Stones

That brings us to another factor that promotes kidney stones: high omega-3 polyunsaturated fat consumption.

Here’s the data:

Older women (NHS I) in the highest quintile of EPA and DHA intake had a multivariate relative risk of 1.28 (95% confidence interval, 1.04 to 1.56; P for trend = 0.04) of stone formation compared with women in the lowest quintile. [11]

Eating omega-3 fats promotes calcium oxalate kidney stones about as much as eating oxalate. The top quintile of dietary oxalate intake has a relative risk of 1.22. [12]  (The top dietary source of oxalate is spinach, by the way.)

So what about EPA and DHA promotes kidney stone formation?  A clue comes from julianne of Julianne’s Paleo & Zone Nutrition Blog; she made a very interesting comment:

A few years ago I started taking a high dose of Omega 3, because of joint inflammation, and other issues. This made big difference for about 3 months, then seemed to not work any more. I talked to a nutritionist friend and she pointed out that according to Andrew Stoll (The Omega 3 Connection) you must take 1000 mg vit C and 500 iu vit E daily or the omega 3 becomes oxidised in your body (cell membranes) and ineffective. I started taking both and in days was back to the original anti-inflammatory effectiveness of omega 3. I have since talked to others about this – for example a psychiatrist whose clients did well on omega 3 for 3 months and then it became ineffective.

Paleo advice from many is to consume a high dose of omega 3, and at the same time reduce carbs. I am wondering if there are people suffering vit C depletion as a result of increased omega 3 consumption as well as too low carbs?

EPA and DHA have a lot of fragile carbon double bonds – 5 and 6 respectively – and are easily oxidized. It’s quite plausible that this lipid peroxidation can lead to oxidation and degradation of vitamin C.

If so, then higher EPA and DHA consumption would increase the flux of oxalate through the kidneys and raise the risk of calcium oxalate stones. It makes sense that the effect is strongest in the elderly, who tend to have the worst antioxidant status.

What Does This Tell Us About the Cause of Stones in the General Population?

Since most kidney stones afflicting the general public are calcium oxalate stones, it seems likely that vitamin C degradation may be the major source of raw material for kidney stones.

If so, then the risk of kidney stones can be greatly reduced by dietary and nutritional steps.

First, the rate of oxidation can be slowed by higher intake of antioxidants such as:

  • Glutathione and precursors such as N-acetylcysteine;
  • Selenium for glutathione peroxidase;
  • Zinc and copper for superoxide dismutase;
  • Coenzyme Q10 for lipid protection;
  • Alpha lipoid acid;
  • Colorful vegetables and berries.

Vitamin C supplementation has mixed effects: its antioxidant effect is beneficial but its degradation is harmful.

Second, electrolyte and water consumption are important. Salt is especially important.

Finally, alkalinizing compounds like lemon juice or other citrate sources can increase the solubility of uric acid.


Zero-carb dieters are at risk for

  • Excess renal oxalate from failure to recycle vitamin C;
  • Excess renal uric acid from disposal of nitrogen products of gluconeogenesis and ketogenesis;
  • Salt and other electrolyte deficiencies from excretion of oxalate, urea and uric acid; and
  • Dehydration.

These four conditions dramatically elevate the risk of kidney stones.

To remedy these deficiencies, we recommend that everyone who fasts or who follows a zero-carb diet obtain dietary and supplemental antioxidants, eat salt and other electrolytes, and drink lots of water.

Also, unless there is a therapeutic reason to restrict carbohydrates, it is best to obtain about 20% of calories from carbs in order to relieve the need to manufacture glucose and ketones from protein. This will substantially reduce uric acid excretion. If it also reduces vitamin C degradation rates, as we argued in our last post, then it will substantially reduce oxalate excretion as well.

Related Posts

Other posts in this series:

  1. Dangers of Zero-Carb Diets, I: Can There Be a Carbohydrate Deficiency? Nov 10, 2010.
  2. Dangers of Zero-Carb Diets, II: Mucus Deficiency and Gastrointestinal Cancers A Nov 15, 2010.
  3. Danger of Zero-Carb Diets III: Scurvy Nov 20, 2010.


[1] Furth SL et al. Risk factors for urolithiasis in children on the ketogenic diet. Pediatr Nephrol. 2000 Nov;15(1-2):125-8. http://pmid.us/11095028.

[2] Herzberg GZ et al. Urolithiasis associated with the ketogenic diet. J Pediatr. 1990 Nov;117(5):743-5. http://pmid.us/2231206.

[3] Sampath A et al. Kidney stones and the ketogenic diet: risk factors and prevention. J Child Neurol. 2007 Apr;22(4):375-8. http://pmid.us/17621514.

[4] “Ketogenic diet,” Wikipedia, http://en.wikipedia.org/wiki/Ketogenic_diet.

[5] Groesbeck DK et al. Long-term use of the ketogenic diet. Dev Med Child Neurol. 2006 Dec;48(12):978-81. http://pmid.us/17109786.

[6] Taylor EN et al. DASH-style diet associates with reduced risk for kidney stones. J Am Soc Nephrol. 2009 Oct;20(10):2253-9. http://pmid.us/19679672.

[7] Gutman AB. Significance of uric acid as a nitrogenous waste in vertebrate evolution. Arthritis Rheum. 1965 Oct;8(5):614-26. http://pmid.us/5892984.

[8] Boyle JA et al. Serum uric acid levels in normal pregnancy with observations on the renal excretion of urate in pregnancy. J Clin Pathol. 1966 Sep;19(5):501-3. http://pmid.us/5919366.

[9] Linster CL, Van Schaftingen E. Vitamin C. Biosynthesis, recycling and degradation in mammals. FEBS J. 2007 Jan;274(1):1-22. http://pmid.us/17222174.

[10] Marengo SR, Romani AM. Oxalate in renal stone disease: the terminal metabolite that just won’t go away. Nat Clin Pract Nephrol. 2008 Jul;4(7):368-77. http://pmid.us/18523430.

[11] Taylor EN et al. Fatty acid intake and incident nephrolithiasis. Am J Kidney Dis. 2005 Feb;45(2):267-74. http://pmid.us/15685503.

[12] Taylor EN, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol. 2007 Jul;18(7):2198-204. http://pmid.us/17538185.

Leave a comment ?


  1. I see you have linked to my website as an example of how low carb paleo dieters are more susceptible to gout. However, I think this is somewhat misleading. The week that I got the gout I was actually eating MORE carbs, not less, and since doing paleo I have only had gout once in two years and the attacks were a lot more frequent before going on this diet.

  2. Gary Taubes argues that gout is caused by sugar/fructose, not protein.


    I’m also curious where someone on a true zero carb diet (meat only) would get oxylates? Are they in meat?

    I wish I could remember where I read about it, but I came across a study a while back that said very low carb diets will shrink kidney stones. If someone were to have a stone that was too big to pass, a VLC diet may shrink it enough to pass. The diet would then have appeared to have “caused” the stone.

    However, that probably wouldn’t explain the stones experienced by the epileptic kids put on keto diets. The confounding factor there, though, is that those diets are awful, being very high in PUFAs.

  3. Intriguing post. Could you clarify about fasting/IF and how that plays into the concern about uric acid build up, etc? Exactly how much should IF’ers be concerned?

    I include rice and sweet potatoes in my diet and have maybe 80 grams of protein per day (165 lb., 6′ male). This may not be exactly 20% of daily calories, but it shouldn’t be super far off. I frequently eat within an 8 hour window or occassionaly do a 20 hour fast.

    I understand that people may be in ketosis when fasting. But shouldn’t my body be able to handle the limited amount of ketosis and gluconegensis (sp), especially when, during times I am eating, protein is moderate? Shouldn’t my situation regarding potential for kidney stones be much better than a true low carber?

    Thanks! Hope that makes sense.

  4. Very interesting post, as always. Like some of your other commenters, I’m curious about a seeming contradiction between high and low carb diets both causing gout. Julianne also has a post about fructose and gout:


    Could it be that either end of the spectrum causes excess uric acid?

  5. Hi Frosty,

    Fructose does cause uric acid. That’s the leading cause of gout etc. on the Standard American Diet.

    Dietary oxalates mostly come from plants but in cases such as infections where vitamin C oxidization is high, vitamin C degradation will be the main source of oxalates.

    There’s a lot wrong with clinical ketogenic diets. There’s not much known about what causes kidney stones to shrink.

  6. Hi Mike,

    I don’t think IFers need be concerned. It takes a lot more than a day to build up a kidney stone.

    I think you’re in good shape.

    Hi Tuck,

    Yes, fructose causes gout. The mechanism is a bit different. Fructose needs a lot of phosphate to be metabolized. That strips phosphate from ATP leaving adenosine which has to be destroyed. Adenosine degradation produces uric acid.

    So fructose, alcohol, and some other things can cause gout.

  7. I have been studying ketogenic diets for epilepsy kids as I believe it is the diet to follow if you have cancer. (you might write about this). As part of this diet, fluids are restricting to 80% of normal. They have experimented with no fluid restriction and the kids do not get kidney stones. So it is the fluid restriction and not the lack of carbs that cause the kidney stones in these kids.

    Are you sure about the studies linking protein consumption to kidney problems? It is a favorite topic of vegetarians and university vegetarian researchers are famed for falsifying data to prove this connection.

    Dr. Eades says that the protein/kidney problem is a vampire myth that will not die even though there are 17,000 studies that show there is no connection.

  8. Hi Jake,

    I don’t believe eating protein causes problems, it’s metabolizing it for energy that releases nitrogen and is potentially problematic.

    So it’s more the carb restriction forcing protein metabolism that’s the problem, rather than protein per se.

    I haven’t mentioned any studies linking protein consumption to kidney problems.

    As you say, electrolytes and water can make a big difference. I don’t think they eliminate the stone risk however.

    And we do recommend ketogenic diets for cancer. But our recommended ketogenic diet has much less protein metabolism: We recommend 200 calories per day from starches and lots of coconut oil for ketogenic medium chain fats, both of which reduce protein metabolism substantially.

    Best, Paul

  9. I just came across this today, you might have seen it, related to kidney disease rather than kidney stones:

    Fruits, Vegetables Slow Kidney Disease Decline in Hypertensive Patients

  10. Hi julianne,

    It does seem like vegetables can be good for you!

  11. Paul you say “Vitamin C supplementation has mixed effects: its antioxidant effect is beneficial but its degradation is harmful.”

    Are there risks of supplementing gram doses of vitamin C? I noticed in previous blog posts you described high intake of up to bowel tolerance of vitamin C is relatively safe and can be very beneficial for fighting an infection.

    Does a daily intake of 2-6gm of vitamin C have possible negative effects of degradation? I suppose that would depend on the current diet and overall health of the subject?

  12. Hi Tyler,

    I had some kidney pain while I was recovering from my scurvy, I wonder if it was small kidney stones. The problem went away after a month or two.

    I think:

    1) If your antioxidant status is good then there is relatively little oxalate production. Vitamin C gets oxidized in two steps, with one electron to a free radical state and then two electrons to DHAA. If your antioxidant state is good it only goes to the free radical state and then back to ascorbate, so there is minimal DHAA degradation.

    2) If you drink plenty of water and take enough salt, the oxalate can generally be excreted and the stone risk is relatively small.

    Since vitamin C helps maintain the other antioxidants, gram doses of vitamin C will over time work to restore the other antioxidants and keep down oxalate production via (1). So the danger is period is when just starting vitamin C after a deficiency or during a stressful infection. But those times are when you most need vitamin C!

    So I wouldn’t avoid vitamin C out of fear of stones. Rather I would try to maintain adequate levels of all the endogenous antioxidants through C, copper, and selenium supplementation.

  13. Great article, and a great series!

    You mention “citrate sources” and lemon juice specifically as “alkalinizing compounds”. Lemon juice has about the same pH as vinegar, and both are acidic (pH of 2.3 to 2.5). Is lemon juice metabolized in a manner that it becomes alkalinizing?

  14. Hi Frank,

    Yes, after oxidation in the body citric acid becomes an alkaline ash.

    Acetic acid remains acidic, but malic acid in apple cider vinegar is alkalinizing.

    The advantage of taking acids for alkalinization as opposed to, say, bicarbonate is that they don’t destroy stomach acid.

  15. Paul,

    Thanks for another great piece of detective work. One of the most interesting parts of this article is the potential contribution of excess omega-3s to kidney stones.

    Yet another reason to steer clear of the increasingly common (and troublesome) recommendation in the paleo world to take up to 30g+/d of fish oil. YIKES!

  16. Hi Chris,

    I haven’t seen that recommendation! Yikes is right!

  17. Julianne, that study is poorly designed. What in the diet is the addition of fruits and vegetables replacing? That’s the key.

  18. This series has been very interesting especially in conjuction with Stephans posts about high carb diets.

    However I’m not convinced that any of the risks discussed are directly caused by low carbs. All of them can be adressed with other aspects of the diet without really altering carb consumption. Obviously eating anything replaces something else in the diet, but other things can be eaten to combat these concerns instead of replacing with a little carbs.

    By no means do I think that zero carb is any better than eating 10%, 20%, 30% or whatever. In the context of an otherwise immaculate paleolithic diet a high precentage of carbs can obviously be tolerated. Prooving what is optimal though as a general rule I think is pretty hard, near on impossible.

    Eating a little safe carbs here and there isn’t going to cause any problem. I don’t think eating zero carb is going to cause a problem either if the dietary deficiencies associated with zero carb are addressed

  19. Hi James,

    These are open questions in dietary science and I don’t expect to be able to resolve them in this series.

    But I do think we can point a number of dangers and pitfalls on very low carb / zero carb diets and help people who want to eat that way to avoid them.

    My expectation is that zero-carb is a diet that can be tolerated by healthy people for an extended period of time, but is not robust to perturbation — either from shortfalls in nutrients, or to infections. I doubt it would improve on the SAD in terms of life expectancy.

    Others may disagree. The evidence is not adequate to make a definitive answer.

    As Stephan’s post shows, we don’t have adequate evidence to address the optimality of high-carb “safe starch” diets either.

    Still, I think the arguments in our book for eating carbs just shy of the body’s glucose needs — 400 to 600 calories, 20% to 30% of a sedentary person’s needs — are sound. I may elaborate on those in the future.

  20. baking soda has been shown to increase endurance and sport performance, presumably via its alkalinizing effect. would lemon juice possibly work for this as well?

  21. This has been a great series. Thanks!

  22. Hi Abby – I would assume so, but I don’t have specific knowledge.

    Jeremy – Thanks! I have a few more installments planned but they’ll have to wait a bit.

  23. Paul,

    I’m on a pretty low carb diet (though beginning to add in safe starches per your recommendations), and I’m wondering what exactly an adequate intake of salt would be. It’s not an issue I was aware of before and I’m just now beginning to learn about it, since most of the time it’s been advised to lower your salt intake no matter what. Should I just salt everything to taste? Or measure it out?

    Is there a way to know if I’m not getting enough? How about too much? Is it even possible, assuming no deliberate supplementation, to get too much salt on a low carb/whole unprocessed foods diet?

    Thanks for the great work you’re doing.

  24. Hi TL,

    The easiest way to tell is to taste it. If salt tastes good, you need more; if it tastes bland, you have enough.

    Then drink lots of water. Keep yourself well hydrated. Then taste salt again.

    My experience has been that if I eat abundant carbs, a quarter teaspoon per day is enough; but if I eat minimal carbs, I need at least a teaspoon per day. Back when I ate zero carb, I kept a small bowl of salt on my desk and would sample it from time to time.

    • I am trying the Volek/Phinney ketosis diet right now, and this sodium issue is rather disturbing. I have to eat 2g extra sodium per day (I take it in the form of bouillon), AND put extra salt on my food, in order not to get light-headed. I have to eat more salt even when salt doesn’t taste particularly good. Maybe I need to drink more water. The 2g is also what they recommend in their book.

  25. I’d like to send a link to this post to someone I know who is diabetic, eats low carb to stay off prescription drugs for diabetes, and has kidney stones, but I’m afraid he might see it as calling for going off low-carb to alleviate the stones. I know you say no-, not low-, carb dieting is a problem, but what advice might you give to someone who has to eat low-carb for his diabetes and has kidney stones? I, as a lay person trying to sift through the science talk, take away from this that staying hydrated, eating adequate salt, getting plenty of vitamin C, and laying off fish oil supplements and polyunsaturated vegetable oils may be helpful. Would you concur?

  26. Hi ethyl,

    Yes, I would concur with all those things. Pretty much the full list in the post, including lemon juice or other citrate source and the other antioxidants mentioned, would be helpful.

    The other key is to try not to be too dependent on protein for energy. For diabetics we recommend a ketogenic diet with lots of coconut oil to produce ketones, and a bit of starch from our “safe starches” — we typically recommend about 50 g / 200 calories from safe starches per day. Between the two of those you can cut down protein metabolism by maybe 500 calories per day which will substantially reduce the uric acid load.

    Best, Paul

  27. Hi,

    Just slightly off topic, I would like to know your views on tea consumption. It seems to be quite an addiction in my house. Not too sure its that healthy though; any views on this topic? I have read that adding milk to your tea, cancels out any benefits consumption would have had.

    Cheers, I’m enjoying your posts.

  28. Hi Jenna,

    We drink green tea daily. I gave it up for 3 months this summer to test whether oxalate reduction was helpful, now I am steeping it a little less long for a milder flavor.

    I saw the milk and tea study also.

    As far as I know tea is healthful. Caffeine, oxalates, and other compounds in tea can be concerns, but as long as the quantities are not too high (and no one knows how much is “too high”) they should be fine. We do recommend tea consumption in the book.

  29. Paul,

    Your series of posts on the dangers of a zero carb diet have been a major revelation. In particular, you have shed new light on two health problems that I have suffered from over the past couple of years. One is dry eyes. The other is kidney stones. Here I’ll discuss the latter, which confirms everything you have said.

    I’ve been on a low carb diet for over eight years. Most of that time I focused on keeping my carbs in the range of 50-100g per day. Almost all my carbs came from vegetables. I ate very little starchy foods and hardly any fruit except berries. So by your definition I was really on a VERY low carb diet. Only in the last year have I taken a more paleo approach (focusing on avoiding wheat, fructose, and vegetable oils rather than carbs per se); however, until very recently I continued to keep my carb intake low.

    A year and a half I ago I suffered two kidney stone episodes — 1st one kidney, then three weeks later the other. I was not able to capture any of the stones, but an analysis of my urine (collected over 24 hours) after the 2nd episode showed that my urine oxalate level was three times higher than normal.

    Prior to my kidney stone episodes I did almost everything wrong that you covered in your post: Besides eating a low glucose diet, I had been eating a fairly high oxalate diet — a lot of spinach and almonds. Also I had been eating a high omega3 diet –about 2 pounds of canned salmon and sardines a week — plus taking supplemental fish oil on the two or three days that I didn’t eat fish. My water intake was low and so was my salt intake.

    On the advice of my urologist, I cut back my consumption of spinach and almonds and increased my water intake. I also started using more salt, although not so much by plan as by taste. About the same time, based on reading Chris Masterjohn’s recommendations on PUFA, I cut back on my consumption of salmon and sardines to about one pound per week. However, I continued to eat a very low carb diet. It has been only in the last few months, after reading your book, that I started to increase my consumption of safe starches (mainly from white rice).

    I have one question about the consumption of safe starches. I usually eat during a 8-10 hour window and fast for 14-16 hours. Would you recommend that the consumption of starches be spread out over the period that I eat (e.g. once at the beginning and once toward the end) rather than mostly consumed in one meal? In your discussion of “Regular Short Fasts” in your book (245-6), you suggest that a 16 hour fast is sufficent to trigger autophagy and there is little danger provided the liver glycogen stores are replenshished by ~400 calories of starchy carbs during the eight hour feeding window. So my question is whether there is a recommended minimum span for the carb feeding window?


  30. Hi Larry, waiting for Paul’s reply I’d like to ask you a question:

    Why have you been so low carb for 8 years?
    I have not seen many people doing such restrictive diet for this long time!

    What beneficts have you had with this diet?

    I did a similar diet (except berries) for 1 year but it has been a complete disaster. I felt drained without energy and my digestion worsened.
    Now I’m going to switch the perfect health diet.


  31. Kratos,

    Like I said, I was on what I considered a low carb diet, not a VERY low carb diet — I was counting the carbs from vegetables (unlike Paul). Basically, I was on an Atkins or Protein Power maintenance diet.

    Also I didn’t mention in my prior comment that I allowed myself cheats when I was away from home — in particular desserts. So about every week or two I indulged in some sugary dessert. (I rationalized this by the fact that my weight would start to drop if I didn’t occasionally indulge in cheats.) However, once I switched to the paleo as opposed to the low carb point of view I eliminated cheats and haven’t eaten anything with significant amounts of sugar or wheat for over a year, and also have been very vigilant about avoiding anything high in omega6 fats, substituting macademia oil, butter, tallow, and coconut oil for olive oil. But as I mentioned, up until reading Paul’s book a couple of months ago, I continued eating a very low carb diet with very little starch. (BTW: without the cheats my weight stabilized to about 5-8 pounds lower than before.)

    Apart from the kidney stones a year and a half ago and dry eyes (which I did not connect to the diet until Paul’s recent post), I felt great — with plenty of energy. And a plus was that my rosacea mostly cleared up once I was on a low carb diet (which probably was due to a diet low in fructose and perhaps wheat).


  32. Thanks Paul,

    I have three more questions:

    1. In your opinion Is there any merit to the idea in nutrition of slow oxidizer and fast oxidizer ‘types’, as I think Dr. Briffa advocates in ‘The True You diet’: I wonder about this in relation to ‘optimal’ fat/carbohydrate/protein intakes individually speaking?

    2. Will it harm to eat carbs, fat to taste, vegetables, alone for a meal a day if one, just felt like it?

    3. Do you know whether there is any research associating negative hormone effects to low carb, high fat diets in women specifically? I ask you this because I have since I was 18, I am now 23, followed a zero carb and then low carb diet: I think this has totally messed up my ‘female’ hormones. I am quite concerned because I am noticing excess hair growth, on my face. I’m not sure what to do, or what is wrong, in order to correct this problem. I am now introducing carbohydrate sources such as white rice to my diet as I think I am deficient in macronutrients/minerals/nutrients. Not that white rice would correct the minerals part. So as a result, I feel like a bit of an idiot, after having a very poor diet beneath the guise of a healthy one for a relatively long period of time. I would buy the book, but I am a mere, student. Also, I would visit and ask my local G.P but my faith in them has eroded to nothingness, it would seem. Possibly because of all the media reports that I happen across, detailing the trauma endured by women having their entire womb removed, and then finding out, there was nothing wrong. Ha, anyway, on that note. . . . . .

    Any thoughts, would be much appreciated.

  33. Jenna, are you on birth control pills? I ask because BCPs contain harmful progestins which act as anti-progesterones in the body (see Dr. John Lee’s writing, and Ray Peat).
    Thyroid is also damaged by BCP use. The excess hair suggests low progesterone relative to estrogen, and/ or elevated testosterone.

    If you are lucky enough to find a skilled practitioner who uses Diagnos-Techs labs, you could run a Female Hormone Panel by saliva. That would give you a lot of good information re: what is happening to your sex hormone levels over the course of a cycle.

    Are you taking any estrogenic supplements such as DHEA?

  34. Hi Michelle, thanks for the response! Your advice is really helpful.

    There’s clearly something amiss, perhaps it will just be a case of checking in with the ‘general practitioner’ after all.

    I’m not on any birth control pills, or any other medications. My sister put me off the idea of BCPs because she had so many complications, such as weight gain, weird periods, etc.

    The main reason I think it must be related to my diet is because I’m not particularly unhealthy, in terms of bending the rules to ‘Paleo’ or the ‘avoiding neolithic agents of disease protocol’. I mean I don’t eat wheat, unless I feel really depressed, which is not very often. I have no aversion to fish, animal fats/proteins; butter, eggs, milk, cheese, lamb, sausages, bacon, chicken, etc. I don’t eat grain or legumes. I don’t eat sugar. I don’t eat loads of fruit. I eat a variety of vegetables. And I am now introducing white rice, and more ‘complex’ carb sources.

    I really just don’t understand it. I mean at my age (particularly) I don’t think it’s a very good thing to be encountering such ‘problems’: does this mean that in a year I will have grown a beard? Or just that my paranoia will have grown big enough to see a fully grown beard?

    I have looked through Ray Peats articles, I find his work very interesting. However, I’m not sure to what extent I can trust in opinions that are so contrary to much of the ‘prevailing wisdoms’ encouraged through the blogosphere; such as ‘avoid fructose, it kills’. Doesn’t Peat encourage sugar in the form of fructose? And ice cream anyone? Hmm.

    Is DHEA legal, sounds good!

  35. What does everybody think of Acai supplements?

  36. Hi Larry,

    I’m glad to hear we helped you understand your dry eyes and kidney stones!

    You did have a lot of risk factors for kidney stones. I think most people probably need 4-5 risk factors at once to get them.

    Re the starches, I think you can eat them anytime you want in your feeding window – all at once, or spread out. (Diabetics should spread them out, however.) We don’t have a minimum span for the feeding window – make it as short as you like.

  37. Hi Jenna,

    1. I’m not familiar with what Dr Briffa has said. In terms of types, I don’t believe there are genetic types, except that ancestral genotypes (like Australian aborigines or Polynesian islanders) tend to have difficulty with toxin-rich Neolithic foods.

    However there are a lot of “metabolic types” resulting from unhealed metabolic damage. Various combinations of food toxins and nutrient deficiencies can produce different kinds of metabolic damage — e.g. see my recent post on choline deficiency, where if you add in a methionine deficiency the pattern of damage radically changes.

    It seems to me that ‘slow oxidizers’ as usually described sound like people who are breaking in the direction of diabetes / obesity, whereas ‘fast oxidizers’ sound like hypothyroid / food toxin / autoimmune damage types.

    In my view, these kinds of classifications are oversimple. It’s best to fix the underlying problems, and I think the Perfect Health Diet should work pretty well for everyone — maybe the ‘slow oxidizer’ type may need a more ketogenic oriented diet, as we suggest in the book for diabetes and obesity. But the dietary difference is not huge.

    2. No. Going with what you feel like is usually a good idea (unless you feel like sugar!). Your body may be missing some nutrient and craving a food that has it.

    3. I don’t know how very low-carb diets interact with female hormones, but now that you’ve mentioned I’ll keep an eye out. As you know, I think zero-carb diets are dangerous and it wouldn’t surprise me if the zero-carb diet or some associated nutrient deficiency is behind your issues.

    Since you can’t afford the book, I’ll email you a copy of the June e-book as a gift. If you find it helpful, then when you’re better off consider buying a copy, or recommending it to your friends.

    Best, Paul

  38. Hi erp,

    Wikipedia has a nice article: http://en.wikipedia.org/wiki/A%C3%A7a%C3%AD_palm

    It sounds like it’s safe, since some traditional cultures got half their calories from it. But the claims of the supplement marketers / spammers are probably unfounded.

    Best, Paul

  39. Thanks for the link Paul.

  40. Hi Paul, What should the diet for a person with some kidney failure issues should look like?

    Less protein, more carbs, less fat?

    I think I have abuse animal protein way too much (although never more than 140 grs) my urine is frecuently clear, sometimes foamy, I checked my blood pressure an it came out 146/70. Im freaking out..having eaten almost primal/wo wheat, sugar, fruits, grains (sometimes potatoes & recently white rice). Really lost here…..could it be that too much red meat on daily basis can cause kidney failure??
    I also supplement with 6.000 ui vit D..maybe I have done it for too long, so maybe Im gonna cut it.
    Sorry for all the Buzz…finally…How do you think about macro ratios for a kidney diet?

    Best wishes,


  41. Hi Marc,

    140 g protein is about double what we recommend, but I think it’s still low enough that it shouldn’t cause toxicity. I wouldn’t expect it to cause kidney damage. It might burden an already-damaged kidney more than is necessary, so it might be prudent to reduce protein if you have kidney damage, but I wouldn’t expect it to be the cause of the damage.

    Our regular diet should be good in terms of macronutrient ratios for kidney disease. I think you should have more carbs than protein, more fat than carbs, but keep polyunsaturated fat low.

    Best, Paul

  42. Paul,

    The PDF E-Book, is brill! At some point I shall definitely be getting the book! Anyway, to the PDF; how you have outlined the ‘issues’ of nutrition, has clarity, and the approach is pragmatic, which ticks all the right box’s in my opinion.


  43. Thanks Jenna! Please let others know you recommend it!

    Best, Paul

  44. Thank you for sharing this it has a very informative content..Diet Kidney I hope more of this comes..

    God bless and more power..

  45. Hi there.. Thank you for sharing this informative contents that i can used or apply in my daily life.. I am looking forward to see more contents like this 🙂

    If you have time please visit this site:
    Kidney Function

  46. Paul,

    I was wondering if two months, every year, of turning up carbs to say, 150 g could offset the dangers outlined here, when the other 10 months of the year is low carb?

    Coupled with the precautions you mention here of course.

    • I have been wondering about the same thing. I read recently that the Inuit would eat berries in the short summer up north. Surely they would not stop themselves at 50g/day 🙂

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