What’s the Trouble With Sweet Potatoes?

We’re continuing with a series on people who have reported something going wrong when they tested some variation of the Perfect Health Diet. (The first post summarized experiences, good and bad; the second looked at difficulties suddenly adding carbohydrates to a very low-carb diet.)

The next issue was reported by Chris Masterjohn; he had trouble with sweet potatoes:

Although sweet potatoes are considered a safe starch on the Perfect Health Diet, they are not very safe for me. When I discovered how yummy sweet potato fries are, I started eating several sweet potatoes per day. Within a few days, I was limping and my neck was stiff. By the end of the week, my limp was extreme. I looked online to see if I was eating anything high in oxalates, and sure enough, sweet potatoes are loaded with them. My symptoms dramatically improved after one day off sweet potatoes and were gone the second day.

Chris’s commenter Lisa also had trouble with sweet potatoes:

I’ve been very achy since I started eating sweet potatoes daily. Why would some of us be maladapted to oxalates?… I’m wondering if after a long stint of LC/paleo eating I’ve become intolerant to oxalates or to starch in general.

Clearly sweet potatoes are not safe for everyone. What might be causing the trouble?

Fructose and Fiber as Possible Confounders

One factor to consider is that there are different varieties of sweet potato. We eat an Asian sweet potato variety which is not nearly as sweet as conventional American sweet potatoes; it has a yellow flesh and a chestnut flavor. It is botanically a yam, not a sweet potato. It looks like this (via “my super sweet twenty-six”):

Like so many modern foods, the standard American sweet potato has been bred for sweetness. Here is data from http://nutritiondata.com comparing 100 g of potatoes, yams, sweet potatoes, and grapes for sugar, starch, and fiber content:

Food Sugar (g) Starch (g) Fiber (g)
Potato 1.2 17.3 2.2
Yam 0.5 23.1 3.9
Sweet potato 6.5 7.5 3.3
Grapes 15.5 0.0 0.9

All have similar calories. Yams are largely sugar-free, but sweet potatoes are intermediate between grapes and potatoes in both sugar and starch content. They are sort of half fruit, half starch.

Thus, it is conceivable that sweet potatoes could trigger an issue like fructose malabsorption; or that fructose or fiber might feed certain gut infections that would not be similarly fed by potatoes.


Chris believed his problem was due to oxalate. Sweet potatoes do contain oxalate, although they are not the only plant foods which do.

In fact, by far the largest source of oxalate in the American diet is spinach. Spinach by itself accounts for over 40% of all oxalate consumed by Americans; potatoes for about 10%. [1] Wheat bran has high levels of oxalate.

Why are oxalates troublesome?  Some people have sensitivities to oxalate. Rarely, genetic defects in the enzymes that degrade oxalate cause a disease called primary hyperoxaluria; this disease afflicts 1 to 3 people in a million.  Other conditions can elevate calcium or oxalate in the urine and increase the risk of calcium oxalate kidney stones. This is especially likely in people who are deficient in magnesium or who don’t eat citrate. [2]

Another pathway by which oxalate might cause trouble is via fungal infections. Candida and other fungi form calcium oxalate crystals in tissue [3,4]; fungi appear to be responsible for the yellow-brown calcium oxalate biofilms which form on stone monuments. [5]

But the literature suggests that oxalate sensitivities are rare. If oxalate sensitivity is present, then it should manifest itself when eating spinach, wheat bran, and other oxalate rich foods. Since Chris has praised spinach and wheat recently, I wonder if it is really the oxalate that caused his trouble.


Another possibility is a class of toxins called phytoalexins.

Ordinarily, sweet potatoes are largely toxin free. But when attacked by fungus or molds, sweet potatoes generate a variety of food toxins. As two papers describe them:

Sweet potatoes contain phytoalexins that can cause lung edema and are hepatotoxic to mice. At least one of these, 4-ipomeanol, can cause extensive lung clara cell necrosis and can increase the severity of pneumonia in mice. Some phytoalexins in sweet potatoes are hepatotoxic and nephrotoxic to mice. [6]

Ipomeanine (IPN), 4-ipomeanol (4-IPO), 1-ipomeanol (1-IPO), and 1,4-ipomeadiol (DIOL) are toxic 3-substituted furans found in mold-damaged sweet potatoes. IPN and 4-IPO are the most toxic, but all produce pulmonary toxicity in cattle and rodents, and 4-IPO induces hepatotoxicity in humans. [7]

Cattle will die if fed mold-damaged sweetpotatoes:

Unfortunate bovine fatalities occurring after ingestion of mold-damaged sweetpotatoes preclude the use of the culled tubers in livestock feed. In cattle, mold-damaged sweetpotatoes induce an acute respiratory distress syndrome resulting in asphyxiation. [8]

Toxins may be present even if mold damage is not visible:

Fermentation of 6 weeks duration was observed to inadequately eliminate the lung, liver, and kidney toxicity caused by mold-damaged sweetpotatoes. In fact, fermentation exacerbated the hepatotoxicity of mold-damaged sweetpotatoes. This is also the first demonstration that sweetpotato regions lacking visible mold damage can induce lung and kidney injury … [8]


Sweet potatoes are generally considered to be one of the least allergenic of foods. However, infants sometimes do have sensitivities to sweet potato. This may reflect an immature gut flora in the infants; perhaps specific bacterial species — possibly including the oxalate-digesting Oxalobacter [9] — make sweet potatoes tolerable? If so, it raises the possibility that adults with incomplete gut flora might also have sweet potato sensitivities.

There is also the possibility of allergies to mold toxins in infected sweet potatoes.

Food Sensitivities as a Diagnostic Tool

Food sensitivities can sometimes be helpful in diagnosing certain health conditions:

  • Leaky gut. People with a leaky gut will have many food sensitivities; people with a healthy gut will have few.
  • Small bowel infections. People with infections of the small intestine will usually have a negative reaction to fructose.
  • Colonic infections. People with infections of the colon may react badly to fiber, and obtain relief on low-fiber diets.

There is a chance that oxalate may benefit fungal infections, so I suppose an oxalate sensitivity could be diagnostic for that, although in my experience fungal infections are usually slow-reacting to food and the response is rarely obvious.


In our book [p 121] we note that all plants make pesticidal toxins. Thus, no plant food can be guaranteed to be safe.

Normally, levels of pesticidal toxins are low in sweet potatoes. But it’s always desirable to inspect sweet potatoes for visible damage, and to discard any that are discolored or show other evidence of toxin production.

I confess to being puzzled as to how sweet potatoes caused Chris’s symptoms. If he tolerates spinach and wheat bran, it seems unlikely that the oxalate in sweet potatoes would be responsible. He might wish to test various foods and try to narrow down the source of his sensitivity.

For our part, we may cease listing sweet potatoes among our “safe starches” and specify yams instead, since a “safe starch” should probably be low in fructose.


[1] 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.

[2] McConnell N et al. Risk factors for developing renal stones in inflammatory bowel disease. BJU Int. 2002 Jun;89(9):835-41. http://pmid.us/12010224.

[3] Takeuchi H et al. Detection by light microscopy of Candida in thin sections of bladder stone. Urology. 1989 Dec;34(6):385-7. http://pmid.us/2688263.

[4] Muntz FH. Oxalate-producing pulmonary aspergillosis in an alpaca. Vet Pathol. 1999 Nov;36(6):631-2. http://pmid.us/10568451.

[5] Pinna D. Fungal physiology and the formation of calcium oxalate films on stone monuments. Aerobiologia. 1993 9(2-3):157-167. http://www.springerlink.com/content/n72l71352t1r0r04/.

[6] Beier RC. Natural pesticides and bioactive components in foods. Rev Environ Contam Toxicol. 1990;113:47-137. http://pmid.us/2404325.

[7] Chen LJ et al. Metabolism of furans in vitro: ipomeanine and 4-ipomeanol. Chem Res Toxicol. 2006 Oct;19(10):1320-9. http://pmid.us/17040101.

[8] Thibodeau MS et al. Effect of fermentation on Sweetpotato (Ipomoea batatas) toxicity in mice. J Agric Food Chem. 2004 Jan 28;52(2):380-4. http://pmid.us/14733525. B76FN5FG89GM

[9] Hatch M et al. Enteric oxalate elimination is induced and oxalate is normalized in a mouse model of Primary Hyperoxaluria following intestinal colonization with Oxalobacter. Am J Physiol Gastrointest Liver Physiol. 2010 Dec 16. [Epub ahead of print]. http://pmid.us/21163900.

Leave a comment ?


  1. Are you sure that’s a Dioscorea? It looks a lot like the Sweet potatoes here and not like the yams I see at the Latin market

  2. Great book and nice post on sweet potatoes / yams. However, I must admit that I’m still confused about how to classify these tubers. How does your recommendation relate to the description of sweet potatoes / yams posted by Mark Sisson? He distinguishes 4 types of sweet potatoes (botanical family Ipomoea) – the photo you show looks most like his Japanese Sweet Potato, or Satsumaimo. He then distinguishes 3 types of yams (botanical family Dioscorea.)

    Here is Mark’s post:

    I’ve got to admit that I’m confused, anything you could do to enlighten me would be much appreciated.

    Thanks for all your great work.

  3. Sweet potatoes are actually low in fructose. Most of the sugar in sweet potatoes is in the form of maltose, which is a disacchiaride of glucose molecules.

    If you search the USDA database for sweet potatoes, then maltose would make up roughly half of the sugars in a cooked sweet potatoes.

    Cooked sweet potatoes have more simple sugars than raw sweet potatoes because the cooking process breaks down the starch into simple sugars.

    According to my calculations, the fructose in sweet potatoes only contributes to about 8% of its total Calories.

    For example, if you eat 1000 Calories in the form of sweet potatoes, then you would only get 20 grams of fructose. This is not much.

  4. Hi Melissa, Ward,

    The picture closely resembles the kind we buy. I could have taken a picture of ours but I was lazy.

    The kind we buy are sold as “Korean Sweet Potato” and I read various places online that these are derived from the yam, not the sweet potato.

    This variety resembles, tastes like, and is very likely closely related in lineage to the Japanese Sweet Potato or Satsumaimo, although I’ve seen those with purple skin and the one we buy has a brown skin. Both have a yellow interior and a less sugary taste.

    Best, Paul

  5. Thanks, Luming.

    According to nutritiondata.com sweet potato sugars are 1/4 fructose, 3/4 glucose; total fructose content is 8% of calories as you say.

    So probably unlikely that fructose is a problem, but as I couldn’t find any likely problems I wanted to cover all the bases.

    Best, Paul

  6. Paul,

    Do you have advice or resources for drilling down further to diagnose health conditions associated with food sensitivities?

    I don’t much more info on this in the book, and while adding more starch to my low-carb diet as advocated in there has helped quite a bit, I still get the random occasional bad case of liquid diarrhea after a meal.. but I can’t for the life of me narrow it down to a particular food.

    It’s happened after a meal of mostly sweet potatoes.. also pineapple seems to be a possible trigger, but I can’t figure it out. Always accompanied by a cloudy film of some sort, and I think as you mention in the book could be a reaction of intestinal mucus shedding..

    Sorry for the graphic detail but this issue has plagued me for a long time and I’m still reaching for answers.

  7. Hi Greg,

    When you get diarrhea, take a handful of probiotics and see if that stops the diarrhea. If so then the problem is bacterial. By handful I mean 20,30,40 something like that, with plenty of water.

    Is it only triggered by plant foods?

    Are the doctors helping you at all? Doctors can take stool samples and get them cultured/analyzed — there are now labs that do PCR to do species analysis. They have other diagnostic tools.

    Best, Paul

  8. From what I’ve read, virtually every variety of “sweet potato” *and* “yam” sold in the US is some kind of sweet potato. Actual yams are said to be rather different in appearance and taste (and practically unavailable in the US). I’ve apparently read the same information as Ward, classifying the Japanese variety as a sweet potato.

    But even if the Japanese variety is a kind of sweet potato, it could still produce different (and less) toxins and pesticides when attacked by fungi, etc. So I could imagine that different varieties of sweet potato might have different effects on different people. All speculation, of course.

    The berries of the Virginia Creeper look very inviting, but are said to be poisonous because of oxalic acid. Birds are supposed to be able to eat them with impunity, though. They can handle the oxalates.

  9. Paul,

    Hard to say because I’m usually eating animal products at meals as well.

    I had a stool sample test last year but didn’t turn anything up, and have taken probiotics to help situation but can’t say if it has made a difference because its so random (it’ll happen once after a meal and then not again for several days).

    20,30,40 pills though? Do you mean a course of that mean or literally downing a whole bunch?

    I’ll try pushing the doc to see if there any other diagnostics to try.

  10. Japanese sweet potato is still Dioscorea. I’ve never cooked true yam, but they sell it here and I might try this week.

  11. Hi Greg,

    I mean a single handful, taken once with a full glass of water.

    It should act within 15 minutes. If it doesn’t stop the diarrhea, then the diarrhea probably isn’t caused by overgrowth of pathogenic bacteria.

    If your diarrhea lasts less than 15 minutes, then obviously this won’t be diagnostic for you.

    As long as everything seems random, I guess you just have to keep improving diet and nutrition on general principles, experiment from time to time, and see if the situation becomes more clear.

  12. Here is the post from Mark’s Daily Apple that was omitted in my previous post:


  13. I have tested both sweet potatoes and regular potatoes after being VLC for quite some time, and I don’t seem to react to potatoes, but sweet potatoes immediately make my colon rumble, and I begin to release a foul smelling gas. This problem however, doesn’t happen when I consume regular potatoes? I think it might be a problem with fructose rather than the oxalates in the tubers.

  14. So far the only sweet potatoes I have been able to tolerate (meaning digest well, without problems with excess gas) are very pale yellow inside and very pale yellowish brown outside.

    The ones I digest well cook up rather like white potatoes, only they are denser. I can’t get them where I live now sadly. 🙁

    Even if I could digest the standard kind that people in the US and Canada favor to make things like sweet potato pie – the really orange inside kind – I find them absolutely disgusting! They are SO sweet and can burn so easily if baked a bit too long. I do like sweet tastes overall, but even thinking about that kind of sweet potato makes me want to gag! LOL

  15. Thus, it is conceivable […] that fructose or fiber might feed certain gut infections that would not be similarly fed by potatoes.

    Interesting. Is it then conceivable that the inverse could also be true, viz. that potatoes, peeled or whole, may support infections that fructose or fiber from other foods does not?

    I ask because bar none, the diet on which I have felt best over the past few years of trying to get well has been a high-sugar fruit diet with a few handfuls of fresh greens. After two to three weeks on each of several attempts at such a lifestyle, I began feeling compelled to bed shortly after dark, sleeping well and jumping fresh out of bed at sunrise; feeling driven to exercise (e.g., to sprint where walking would suffice, or to drop and do pushups)–and actually recovering from the workload; and experiencing smooth skin, clear eyes and pink gums and tongue for the first time in years. I also enjoyed a heightened cognitive life during these periods, able to sustain focus on books, conversation and work in a way I usually lack, a very calm, collected way that is probably to be considered normal.

    I cut short the last fruit feast about ten months ago, lacking the funds and space for mounds of produce and concerned at the possibilities of malnutrition (seen, in my experience, among most raw-food vegans with average to low caloric intakes) and fructose toxicity (not sure where I stand on this now, but am in the presence of health issues more inclined to side with you), opting to meet my calorie goals with potatoes, which were accompanied later on by more PHD-friendly fare (including animal products, to be clear). These choices really helped me put on much needed mass, but just a week of experimentation with white rice as my safe starch reveals that the potatoes might have been holding at bay the aforementioned health improvements, previously associated with some magical component of fruit.

    You add weight my hunch that this is simply a leaky gut/sensitivity issue, but the possibility of infection I find very interesting. With any luck, I may never have to know. For now I’ll be adding sweet potatoes back in to see how they do on their own.

    (Meant to post on this in the Jan. 4 post on PHD experiences. Apologies for the length, but I wanted to hammer home the folly of sticking for months or even years with what clearly doesn’t work…)

  16. Hi Lillea,

    I agree with you on sweetness. The less sweet the variety, the better I like it.

    You might try shopping at an Asian supermarket, most of the Asian varieties are not very sweet. Mark Sisson must be referring to a different variety than we’re familiar with when he says Japanese sweet potatoes are very sweet.

    Hi gh,

    Potatoes have significantly more fiber than rice, so yes, they would tend to feed colonic infections more than rice or sugar.

    An all-fruit diet may be tolerable for a while but the fructose will tend to promote bacterial infections, malnutrition is a concern as you say, and fructose really becomes toxic if combined with polyunsaturated fats. I don’t think that diet would age well.

    Good luck!

  17. A quick and perhaps oversimplified thought I had while reading this post.

    1. From Chris: “…When I discovered how yummy sweet potato fries are, I started eating several sweet potatoes per day…”

    2. From Lisa: “…I’ve been very achy since I started eating sweet potatoes daily…”

    Could there be a relationship between the quantity of sweet potato that is being consumed on a DAILY basis and the occurrence of these symptoms?

    From page 115 of The Perfect Health Diet eBook:

    The toxicologists’ rule: “The dose makes the poison.”

    Thanks for all of the great information!

  18. Hi Paul,

    Since you’ve mentioned chronic fungal infections in your last couple of posts, I have a question.

    Some quick background first: I came to the Paleo diet in March 2010 (gluten-free two years prior to that) as an experiment to heal some chronic skins conditions — seborrheic dermatitis and pruritus ani. I saw no improvement, but the diet made so much sense that I will never go back to the low-fat vegan/vegetarian diet I was previously eating. In the last two months, since finding your blog/book, I have been increasing fat consumption and adding in starches (sweet potatoes cause no problem for me and make meals much more enjoyable!). Though not tied to a specific food that I can tell, I’m now also experiencing cracking of eyelids and earlobes, rough patches on arms/shoulders, and poor salivary glad production that gives my mouth a nasty pasty quality at times. Doctors have been no help on the skin front — prescribing only cortisone creams and anti-fungal shampoos, which did not work for very long. Trying to engage them in a discussion of what is causing these symptoms turned out to be a waste of time (since apparently such a discussion does not fit within the Kaiser Permanente protocol!).

    I’m surprised that the drastic diet change didn’t help. It seems like I must have a chronic inflection or fungal overgrowth that requires more drastic measures. Step 4 of your book interests me; do you think fasting could be beneficial? An antifungal like Nystatin? Any thoughts you have would be much appreciated.


  19. Thanks Paul!

    There aren’t any Asian markets where I live now, but there were dozens in Vancouver BC Canada where I used to live. But maybe I’ll be fortunate and the local grocer will bring something in for me on request.

  20. No digestion problems here but I did eat some sweet potato over the holidays (they’re very uncommon in europe and it might be a decade ago I ate them for the first and last time since) and have to say I don’t like the sweetness at all. Just tastes wrong to me, like when you take a white potato and cook it with a lot of sugar!
    I’m glad to hear it’s even safer to stick with my ordinary white potatoes. 🙂

  21. To Jess, Did you ever consider your omega 6/3 ratio?

  22. they are not sweet potatoes by the look of it
    but in America sweet potatoes are misnamed as yams and vice versa from what I’ve heard.
    Kitivan studies show sweet potatoes to be one of the most healthful foods from one of the most healthy peoples who eat up to 90% pf their diet as sweet potatoe



  23. Hi Jeremy, Great point! Quantity matters.

    Hi Jess,

    Fasting will not help and would probably hurt. Fasting is good for intracellular infections (parasitic bacteria, viruses) because resource scarcity promotes autophagy, but not good for extracellular infections which consume a lot of calories, esp. glucose.

    I would aim for 400 glucose calories a day, keep omega-6 low and eat 1 lb salmon/week in line with Hans’s suggestion, and also follow our supplement regimen including D and C. Micronutrition may be very important for you. I would take the B vitamins listed on our supplement recommendations page too, just to rule out those deficiencies as possibilities. I wouldn’t do extensive fasting unless you conclude this may be caused by a viral infection.

    Since it sounds like a fungal infection and the anti-fungal shampoos may have helped, I would ask doctors to experiment with an antifungal drug. Diflucan is fairly well tolerated.

    If it is viral in origin, I don’t know whether there are drugs that may help. However, in that case fasting would probably prove beneficial. You will have to experiment a bit. But I would fix micronutrients first, that doesn’t take long and could have a big payoff.

    Best, Paul

  24. Hi snaider,

    Thanks much! That is a fascinating set of links.

    I was totally unaware of a vitamin K2 – oxalate connection and if K2 deficiency induces oxalate sensitivity, then it would not be a surprise that it is fairly common.

    I also wasn’t aware of the autism link.

    Of course Chris is well aware of the importance of K2 so I would be surprised if he is deficient! But maybe he doesn’t supplement.

    Very interesting. Thank you!


  25. Thanks, Paul. I really appreciate your insights.

    I’m going to try these diet/supplementing tweaks and will return to the doctor to discuss an anti-fungal drug if diet alone doesn’t create some improvement. I think my omega 3/omega 6 ratios are probably pretty decent, but I can see where there is room for improvement. For instance, I eat pasture-raised meats, but tend to emphasize chicken and pork over lamb and beef. I doubt I ever eat more than 3/4 lb of salmon in a week and I’ve been pretty free with the olive oil, almonds, and eggs. I’m consistent about supplementing D, but not C and the B family. So it’s time to make some adjustments and we’ll see what happens! Thanks again.

  26. I too tend to react badly to sweet potatos (the orange fleshed tubers usually mislabeled as yams)– specifically, water retention — which I thought was simply due to the high carbs. When I say sweet potato, I am referring to the orange tubers that many Americans refer to as yams. Yet I don’t seem to have this problem with a tuber sold at Whole Foods labeled “Japanese Yam.” It is darker red skinned and if the flesh is white — but pale yellowish after being cooked. The guy in the produce section said that Japanese Yams sell out fast and they are the darker red skinned and if you scrape a bit of the skin away, the flesh appears white when raw. Is this what you refer to as Korean Yam?

    Also, what are your thoughts on the heirloom potatoes — fingerling, purple and red fleshed varieties? I tend to tolerate these — especially the purple variety — much better than the orange
    sweet potato (“yam”). I also prefer the less sweet flavor of these potatos and the Japanese Yam over the orange sweet potato.

    PS: I just received your book and am finding it quite interesting. As a female with uterine fibroids, I was interested in what effect if any your diet had on your wife’s fibroids and other gynological issues. Specifically, I am curious if she experienced actual shrinkage of the fibroids, not just alleviation of symptoms such as cramping and/or bleeding. I have very large fibroids on the outside of uterine wall which have caused me no symptoms (grew silently) until recently because of their bulk — and my periods were always pleasant — light and totally cramp/pain free. I credit low-carb paleoish for the lack of cramps and pain. I am quite slender.

  27. when i was in the US recently i bought ‘yams’ from wholefoods with yellow flesh – looked just like your picture. But they were as sweet as what i am used to as ‘sweet potatoes’ (orange fleshed), which is confusing!
    Also, it kinda sucks that i’ve never seen ‘yams’ here in the UK, only sweet potatoes. Once winter squash season is over, i’m not quite sure the best carb sources to eat in the summer!

  28. Hi Annie,

    All this botany and the misnaming is rather confusing! It’s very likely that our Korean one is the same as that “Japanese yam.” Shou-Ching is going to buy some of every kind in her next trip to the supermarket and we’ll take pictures and taste them. We like the low-sugar varieties and rarely eat any with a very sweet taste.

    We do eat heirloom potatoes, including purple fingerlings. I think they are healthy, the anthocyanins are toxic but as I argued in my cranberries post, much more toxic for gut pathogens than for us so hopefully beneficial overall!

    Re fibroids, Shou-Ching’s fibroids had shrunk in volume by 90% at her last ultrasound but we don’t know whether or how much we can credit our diet for that; she had medical treatments and there are confounding factors. The diet did greatly improve her health. Soy (soy milk, tofu, vegetable oil) was the biggest culprit. She made homemade soy milk from soybeans and drank it every day.

  29. Jeremy beat me to the punch!

    My first thought about Chris’s statement was, “My gawd, several sweet potatoes a DAY?!”

    Especially if he wasn’t used to eating that much fructose consistently, I would think that a sudden influx like that might spin anyone’s system around a little.

    (And I will also state for the record that I have a great deal of respect for Chris and the information he publishes on his blog and never miss a post.)

  30. Thanks for the insights, Paul. I doubt the oxalates in spinach are anywhere near as bioavailable as in sweet potatoes, but I’ve never eaten an enormous amount of spinach and probably not enough wheat either.

    Of course I have little direct evidence that oxalates are the issue, and when I have a chance I’ll look at the data you posted and some other stuff and come to a better decision about the plausibility of that explanation.

    Chris B., even if it were obviously harmful to use sweet potatoes as a primary source of calories, I would not expect such a dramatic effect in less than a week. I find fructose an incredibly implausible explanation, given that there is about 3g/100g according to what Paul posted above, if that sugar is sucrose. I eat fruit and don’t get a limp from it.


  31. Hi Paul
    FWIW I checked (b/c the starch values do not agree with my calorie counter) the nutrient values for sweet potato and potato, in both cases raw and per 100gm. I get different values (gm; yours/mine):
    Sweet Potato:
    Sugar – 6.5/4.2
    Starch – 7.5/12.7
    Fiber – 3.3/3.0
    Sugar – 1.2/0.8
    Starch – 17.3/15.4
    Fiber – 2.2/2.2
    I used the same source (ultimately USDA). Did you use baked/cooked values?

  32. Hi Morris,

    This wasn’t the precise one I used but the numbers are close:


    I would have used cooked since presumably that is how they were eaten.

  33. Hey Paul,

    What is your opinion on starch feeding fungal infections such as Candida? Many anti-candida type diets regard starch as a ‘candida feeder.’ Is there any truth to this? I have an eerie suspicion that I might have some sort of fungal infection, so I am reluctant to add starch back into my diet.

  34. Hi Robert,

    What I know best is my own experience. I’ll tell this more completely in the upcoming “My Story” series but I would get severe fungal infection in two situations: the first ~4 weeks of antibiotics and when eating zero-carb.

    Since the immune response to fungi requires and consumes glucose, I’m guessing a zero-carb diet suppresses anti-fungal immunity and lets them go wild.

    In my case, I had bacteria-infected white blood cells and I would get a big drop in leukocyte count whenever I started antibiotics, accounting for the other pattern.

    It’s likely my fungal species were Candida, as that is what dominated the skin cultures.

    So I would definitely not avoid starches if you have candida.

    Fiber should be worse since the colon is the main reservoir for Candida and the small intestine isn’t fungal friendly. Most starch will be digested in the small intestine and Candida may never see it, only the resistant starch. So fiber-poor starches like rice would be the best bet.

    Best, Paul

  35. I am sorry, but what do you mean in your article when you say

    “This is especially likely in people who are deficient in magnesium or who don’t eat citrate”

    where do I get citrate from, just citric acid? what about various kinds of citrate (when I tried to look it up, magnesium citrate, calcium citrate, zinc citrate,… came up), so any particular citrate you had in mind?


  36. Hi Elie,

    Yes, the best source is citrus fruit like lemon. Citrate is a salt of citric acid, formed by bonding citric acid with a metal like the ones you name. The salts dissolve in the body so the magnesium etc and citric acid come loose.

    I’m going to do some posts on lemons, citrate, and their health benefits soon. Preview: Lemon juice is good for you!

    Best, Paul

  37. Thanks for your quick response. I am just always worried about diet and oxalate since I suffer from occasional kidney stones. So, any mention of calcium based stones catches my eye…

    p.s. I really enjoy your book. Well done.

  38. Hi Paul,
    I still haven’t finished reading your book but I have a question for you regarding sweet potatoes in the case of Pre diabetics who secrete a large amount of insulin.My pancreas seem to secrete quiet a lot of insulin even when I take around 8 gm carbohydrate from 40grams of sweet potato with protein and fat from meat ,which results in hypoglycemia within few minutes to one hours time.
    You have advised diabetics 200 cals from carbohydrates including starch but what about in the case of a pre diabetic for whom carbs such as starch tends to make the body release quite lot of insulin? Should we stick to carbs from non-starchy vegetables that doesn’t force the body secrete high insulin?


  39. Hi nada,

    If you can find foods that enable you to get sufficient carbohydrate calories without developing hypoglycemia, then I would encourage you to eat those.

    But I am a bit surprised that sugars would be better for you than starches.

    There’s some evidence that mixed glucose-fructose as in fruit may bring more rapid glycogen manufacture and thus maybe lower insulin spikes. So possibly fruit would work better for you.

    I would also strongly recommend coconut oil, whose shorter chain fats are reduced to ketones which serve as an alternative fuel for glucose-deprived tissue. This would make hypoglycemic effects less severe. Since you sound very low-carb, the ketones from coconut oil should be very valuable for you.

    Best, Paul

  40. Thanks for taking the time to respond Paul!

    I have tried fruits too but they have the same effect and I end up binging.But let me give it one more try with different fruits this time.

    Also thanks for the coconut oil suggestion.I shall definitely give it a try.I have been using coconut oil to cook eggs.I just need to increase the quantity I take.

  41. Perfect Health Diet » Dieter’s Dessert: Taro Coconut Cream Soup - pingback on January 16, 2011 at 9:41 pm
  42. Hmm… Here’s something interesting about yams too.

    Staffan Lindeberg’s Food and Western Disease,

    page 186:
    “Jüptner was originally a gynaecologist and obstetrician. During his five years as a doctor on the Trobriand Islands with its 12 000 inhabitants (in 1990 there were roughly 25 000), he diagnosed 10-15 cases of ovarian cancer, which is a higher incidence than in the rest of Papua New Guinea (P < 0.02)(1231) or in the USA (P < 0.008)(709).

    page 191:
    "While irrelevant to most readers, the use of yam (Dioscorea batatas) as a staple food may also not be advisable for women with ovarian cancer. A high intake of yam could likely result in a high uptake of diosgenin, an endocrine disruptor with contraceptive properties(6,64,148,1976). Speculatively, this could explain the seemingly high rate of ovarian cancer in the Trobriand Islands."

  43. Thank you, Valtsu, that’s new to me.

    A good reminder that no one plant species should dominate the diet.

  44. Thursday January 20 | Sno Valley CrossFit - pingback on January 22, 2011 at 3:43 pm
  45. I seem to have some sensitivity towards yam (Japanese, white flesh), potato, and sweet potato (orange flesh). When I eat more than 3/4 cup, I will have body/joint aches that move around, etc.

    (Earlier, when I was recovering from eye inflammation, my eye pain would flare up after I eat certain foods. That include: citrus fruits, wheat, potato, sweet potato, yam, sugar.)

    Anyway, I go by the Perfect Health Diet for the most part. But I also seem to have sensitivity towards dairy, even raw, or cultured. I seem to get constipated on them, and somehow my mind just somehow feels more cloudy/heavy.

    (again, very small quantity, like one slice of cheese, is okay)
    I am not giving up on butter/ghee just yet. So far, I have not detected any adverse effect from having them.

    Also, I have brown rice (sometimes sprouted)/ soy occasionally and I seem to do okay on them.

    I don’t think there is one safe list for everyone, or even one list that’s good for one person for life. Our bodies change and dietary need/ sensitivity will change.

  46. Hi Paul, I have some more questions for advice about diet/supplements for treating fungal infections and digestive problems. I figured I’d post it here because Jess had similar questions above. As you know I was diagnosed with gastroparesis and have numerous digestive problems – mostly vomiting, belly aches and bloating. Thanks to your recommendations I have had a couple of blood and stool tests done in order to determine the cause(s). No bacterial infections came up, but a deficiency in Enterococcus spp and low counts of Lactobacillus spp were found. No parasitic infections were found. But yeast/fungal infections of C.glabrata and R.rubra were found (the lab recommends Nystatin for these). Also, stool analyses revealed a moderately high fat content, undigested food particles and a green color. Furthermore gluten sensitivity (slightly elevated IgA), lactose intolerance (from biopsy) and histamine intolerance (through dietary challenge procedure) were found.
    I am sticking to the perfect health diet (but avoiding high histamine foods) and taking the main recommended supplements plus digestive enzymes. I would like to ask my doctor to prescribe nystatin and want to start on a good probiotic and the extra B vitamin supplements. Do you have any other supplement suggestions? Also I was wondering if given the fungal infections is a ketogenic diet the best solution? I find that I feel better when avoiding carbs (for some reason especially rice goes badly, but potatoes seem ok), yet I often crave sweets (so i’ll drink something sweetend with glucose syrup) and never seem to get into ketosis.
    Any advice you may have is very welcome 🙂
    All the best, Claire

  47. Hi Claire,

    I’m glad you’re making progress! To identify pathogens is important. I think fungal infections are far more common than people realize. It’s interesting that they might be able to cause gastroparesis.

    Some things that may help against fungal infections:
    1) Probiotics. Threelac contains organisms effective against fungi. Also high-dose probiotics might help.
    2) Coconut oil.
    3) Horopito (Kolorex). An antifungal herb.
    4) Iodine supplementation. Build up slowly.
    5) Glucose and protein intake. Don’t be low on protein+carbs. But it’s good to get carbs in a fast-digesting form, like glucose syrup or rice syrup. If you tolerate potatoes, do those.
    6) Eliminate fructose and alcohol and wheat and omega-6. This goes without saying, but I think these are all significant for fungal infections.
    7) Supplements — selenium, zinc, copper, chromium, iodine, vitamin C, vitamin D are all important. Iron is also important, if you are menstruating you should check iron status.
    8 ) Cranberries or other anthocyanin rich foods may help.
    9) Fermented foods have more diverse bacterial species than probiotic supplements, and are helpful. I would avoid probiotic supplements that have any yeast, including S. boulardii.

    It’s good to alternate Nystatin and Diflucan because they can develop resistance against the drugs. I do recommend you take those drugs.

    I’m not sure you want to be in ketosis. If you do, it would be better to get their by supplementing short-chain fats and ketogenic amino acids (lysine, leucine) than by cutting carbs and protein.

    Above all the key is optimizing immune function with good nourishment. Avoid long fasts.

    Best, Paul

  48. thanks so much for the advice 🙂 !!! i’ll let you know how it pans out. best, claire

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