Dangers of Zero-Carb Diets, II: Mucus Deficiency and Gastrointestinal Cancers

Jan Kwasniewski developed his Optimal Diet something like 40 years ago and it has become extremely popular in Poland.

Kwasniewski recommended that adults should eat in the ratio

60 g protein – 180 g fat – 30 g carbohydrate

In terms of calories this is roughly 240 calories protein / 1640 calories fat / 120 calories carbohydrate on a 2000 calorie diet.

The Perfect Health Diet proportions are more like 300 calories protein / 1300 calories fat / 400 calories carbohydrate.  So the diets would be similar if about 300 calories, or 15% of energy, were moved from fat to carbohydrate in the form of glucose/starch (not fructose/sugar!).

Note that we recommend obtaining at least 600 calories per day from protein and carbs combined. This ensures adequate protein for manufacture of glucose and ketones in the liver. But the Optimal Diet prescribes only 360 calories total (less in women), suggesting that gluconeogenesis cannot, over any long-term period, fully make up for the dietary glucose deficiency.

In the book, we note that a healthy body typically utilizes and needs about 600 glucose calories per day. On the Bellevue All-Meat Trial in 1928 Vilhjalmur Stefansson ate 550 protein calories per day, which is probably a good estimate for the minimum intake needed to prevent lean tissue loss on a zero-carb diet.

With only 360 carb plus protein calories per day, the Optimal Diet forces ketosis if lean tissue is to be preserved. Since at most 200 to 300 calories per day of the glucose requirement can be displaced by ketones, the Optimal Diet is living right on the margin of glucose deficiency.

Gastrointestinal Cancers in Optimal Dieters

I learned over on Peter’s blog that Optimal Dieters have been dying of gastrointestinal cancers at a disturbing rate. Recently Adam Jany, president of the OSBO (the Polish Optimal Dieters’ association), died of stomach cancer at 64 after 17 years on the Optimal Diet. Earlier Karol Braniek, another leader of the OSBO, died at 68 from duodenal cancer.

A Polish former Optimal Dieter who has now switched to something closer to the Perfect Health Diet noted that gastrointestinal cancers seem to be common among Optimal Dieters:

The impression we get is that there’s rather high occurrence of gut cancer, including stomach, duodenum, colon … [source]

I want to talk about why I think that is, since the danger that the Optimal Dieters are discovering was one of the key factors leading us to formulate and publish the Perfect Health Diet.

Zero-Carb Diets Can Induce Mucus Deficiency

I ate a high-vegetable but extremely low-carb diet from December 2005 to January 2008. At the time I thought I was getting about 300 carb calories a day, but I now consider this to have been a zero-carb diet, since I don’t believe carb calories are available from most vegetables. Vegetable carbs are mostly consumed by gut bacteria, whose assistance we need to break down vegetable matter, or by intestinal cells which consume glucose during digestion.

Throughout my 2 years on this zero-carb diet, I had dry eyes and dry mouth. My eyes were bloodshot and irritated, and I had to give up wearing contact lenses. Through repeated experiments, I established that two factors contributed to the dry eyes – vitamin C deficiency and glucose deficiency. After I solved the vitamin C issue, I did perhaps 50 experiments over the following few years, increasing carbs which made the dry eyes go away and reducing them which made them immediately come back. This established unequivocally that it was a glucose deficiency alone that caused the dry eyes.

Rebecca reports similar symptoms in herself and her low carb friends.

This is also a well-known symptom during starvation. As a review cited by LynMarie Daye (and referenced by CarbSane in the comments) notes,

Since hepatic glycogen stores are depleted within 24 h of fasting, blood glucose concentrations are maintained thereafter entirely through gluconeogenesis. Gluconeogenesis is mainly dependent on protein breakdown (a small amount comes from the glycerol released during lipolysis) and it thus results in protein wasting. It is the effects of protein malnutrition that lead to the eventual lack of ability to cough properly and keep the airways clear, in turn leading to pneumonia and death during prolonged starvation; hypoglycaemia does not occur. [1]

Another common symptom of very low carb diets is constipation. This is often attributed to lack of fiber, but I am skeptical. I will get to the various possible causes of constipation in a future post, but for now I’ll just point out that a deficiency of gastrointestinal mucus would create a dry colon and cause constipation.

What connects a zero-carb diet to dry eyes, dry mouth, dry airways, and dry gastrointestinal tract?

Tears, saliva, and mucus of the sinuses, airways, and gastrointestinal tract are all comprised substantially of glycoproteins called mucins. Mucins are primarily composed of sugar; they typically have a number of large sugar chains bound to a protein backbone.

For instance, the main mucin of the gastrointestinal tract, MUC2, is composed of a dimerized protein – each protein weighing 600,000 Daltons individually, so 1.2 million Daltons for the pair – plus about 4 million Daltons of sugar, for a total mass of 5 million Daltons. In the mucus, these large molecules become cross-linked to form “enormous net-like covalent polymers.” (source)

If, for whatever reason, mucin production were halted for lack of glucose, we would have no tears, no saliva and no gastrointestinal or airway mucus.

Mucin Deficiency Causes Cancer

There is a strong association between mucus deficiency and gastrointestinal cancers.

H. pylori is the strongest known risk factor for stomach cancer. [2] H. pylori infection is found in about 80% of gastric cancers. [3] One reason H. pylori promotes stomach cancer so strongly may be that it diminishes mucus in the stomach, as this photo shows:

Top: Normal stomach mucosa. Bottom: Stomach mucosa in an H. pylori infected person.

Scientists have created mice who lack genes for the main digestive tract mucins. These give us direct evidence for the effects on cancer of mucin deficiency.

Experiments in Muc1 knockout mice and mice with Muc1 knockdown have shown that under Helicobacter infection, mice deficient in Muc1 develop far more cancer-promoting inflammation than normal mice. [4]

The main mucin of the intestine is Muc2. The group of Leonard Augenlicht of the Albert Einstein Cancer Center in New York has studied mice lacking Muc2. They develop colorectal cancer. [5]

Tracing backward one step toward the source of mucin deficiency, the sugars in mucin are built from smaller pieces called O-glycans. It has been shown that mice that are deficient in O-glycans are prone to colorectal cancer: “C3GnT-deficient mice displayed a discrete, colon-specific reduction in Muc2 protein and increased permeability of the intestinal barrier. Moreover, these mice were highly susceptible to experimental triggers of colitis and colorectal adenocarcinoma.” [6]

Nutrient Deficiencies Can Also Play a Role

Some micronutrients are required for mucin production – notably vitamin D. [7, 8] Poland is fairly far north, and many of the Optimal Dieters could have been low in vitamin D.

Other important micronutrients for cancer prevention are iodine and selenium. Poland in particular had the lowest iodine intake and among the highest stomach cancer death rates in Europe. After Poland in 1996 began a program of mandatory iodine prophylaxis, stomach cancer rates fell:

In Krakow the standardized incidence ratio of stomach cancer for men decreased from 19.1 per 100,000 to 15.7 per 100,000, and for women from 8.3 per 100,000 to 5.9 per 100,000 in the years 1992-2004. A significant decline of average rate of decrease was observed in men and women (2.3% and 4.0% per year respectively). [9]

So among the Polish Optimal Dieters, the elevated gastrointestinal cancer risk caused by mucin deficiency may have been aggravated by iodine and sunlight deficiencies.


A healthy diet should be robust to faults. The Optimal Diet is not robust to glucose deficiency.

There’s good reason to suspect that at least some of the Optimal Dieters developed mucin deficiencies as a result of the body’s effort to conserve glucose and protein. This would have substantially elevated risk of gastrointestinal cancers. Thus, it’s not a great surprise that many Optimal Dieters have been coming down with GI cancers after 15-20 years on the diet.

We recommend a carb plus protein intake of at least 600 calories per day to avoid possible glucose deficiency. It’s plausible that a zero-carb diet that included at least 600 calories per day protein for gluconeogenesis would not elevate gastrointestinal cancer risks as much as the Optimal Diet. But why be the guinea pig who tests this idea?  Your body needs some glucose, and it’s surely less stressful on the body to supply some glucose, rather than forcing the body to manufacture glucose from protein.

Fasting and low-carb ketogenic diets are therapeutic for various conditions. But anyone on a fast or ketogenic diet should carefully monitor eyes and mouth for signs of decreased saliva or tear production. If there is a sign of dry eyes or dry mouth, the fast should be interrupted to eat some glucose/starch. Rice is a good source. The concern is not only cancer in 15 years; a healthy mucosal barrier is also essential to protect the gut and airways against pathogens.

Related Posts

Other posts in this series:

  1. Dangers of Zero-Carb Diets, I: Can There Be a Carbohydrate Deficiency? Nov 10, 2010.
  2. Danger of Zero-Carb Diets III: Scurvy Nov 20, 2010.
  3. Dangers of Zero-Carb Diets, IV: Kidney Stones Nov 23, 2010.


[1] Sonksen P, Sonksen J. Insulin: understanding its action in health and disease. Br J Anaesth. 2000 Jul;85(1):69-79. http://pmid.us/10927996.

[2] Peek RM Jr, Crabtree JE. Helicobacter infection and gastric neoplasia. J Pathol. 2006 Jan;208(2):233-48. http://pmid.us/16362989.

[3] Bornschein J et al. H. pylori Infection Is a Key Risk Factor for Proximal Gastric Cancer. Dig Dis Sci. 2010 Jul 29. [Epub ahead of print] http://pmid.us/20668939.

[4] Guang W et al. Muc1 cell surface mucin attenuates epithelial inflammation in response to a common mucosal pathogen. J Biol Chem. 2010 Jul 2;285(27):20547-57.  http://pmid.us/20430889.

[5] Velcich A et al. Colorectal cancer in mice genetically deficient in the mucin Muc2. Science. 2002 Mar 1;295(5560):1726-9. http://pmid.us/11872843.

 [6] An G et al. Increased susceptibility to colitis and colorectal tumors in mice lacking core 3-derived O-glycans. J Exp Med. 2007 Jun 11;204(6):1417-29.  http://pmid.us/17517967.

 [7] Paz HB et al. The role of calcium in mucin packaging within goblet cells. Exp Eye Res. 2003 Jul;77(1):69-75. http://pmid.us/12823989.

[8] Schmidt DR, Mangelsdorf DJ. Nuclear receptors of the enteric tract: guarding the frontier.  Nutr Rev. 2008 Oct;66(10 Suppl 2):S88-97. http://pmid.us/18844851.

[9] Go?kowski F et al. Iodine prophylaxis–the protective factor against stomach cancer in iodine deficient areas. Eur J Nutr. 2007 Aug;46(5):251-6. http://pmid.us/17497074.

Leave a comment ?


  1. AMAZING!!! Thank you!
    Hi Paul, I had to write to you to thank you for your work on mucin production and zero-carb diets!
    I’ve been on a strict Ketogenic diet of 1 1/2 years and have been suffering with severe dry mouth, dry eyes, dry nose, dry windpipe, dry colon and digestive tract. I’ve been treated by 7 different Specialists and been subjected to massive battery of tests – seeking Sjogren’s disease and other autoimmune diseases. I’m not out of the woods yet, but since reading your article, I reintroduced safe starches and fruit on a daily basis. I’m happy to report, that I am now producing saliva again and my nose is producing mucous!
    I want to thank you for your tremendous work. Ignore the skeptics! You are BANG ON… A low-carb diet is NOT for everyone!!
    Cheers. Grant

    • ***UPDATE – Aug 23, 2018
      I am now producing saliva and mucous at “normal” rates. The only things I brought back into my diet to accomplish this is: sweet potatoes and blueberries/bananas.
      Question for Doc Paul:
      I’m still having dry, burning eyes. Is it possible I should be adding other starches like Rice?? Thanks for all you do, Paul!

      • Unless you are eating 3 lb per day of sweet potatoes and blueberries and bananas, you probably need more carbs. Try white potatoes or rice.

        Best, Paul

        • Thank you Paul!
          One more question:
          Could my long-term mucin deficiency have caused a disruption of my gut microbiome…even leading to depression?

        • Posts like these make me keep coming back. it seems that mucous is almost is like the ayurvedic concept of kapha.

  2. Optimal diet is NOT zero Carb.. your title is misleading. Please change title from zero carb to keto or optimal diet.. thanks and have a nice day

  3. Great article in a great series.

    I think you’ve made a serious error by describing your diet as ‘zero carb’ when you were eating volumes of high fiber veggies.

    Zero carb happens when no veggies pass your lips.

    The symptoms you describe that led you to begin experimenting away from your program scream ‘oxalate toxicity’.

    I too experienced similar symptoms when eating keto. They continued when I finally eliminated plants entirely.

    I discovered I was eating 1 to 2 grams of oxalate a day on keto – a toxic load – then I began dumping oxalate rapidly when I eliminated plants entirely.

    After a really dreadful four day illness with lots of neuropathy the symptoms went away entirely – to include the eye-gunk-oxalate-shedding.

    Hope this is helpful!

  4. Paul,

    I just purchased the audio book of “The Perfect Health Diet”. Looking forward to hearing it!
    Question: Have there been any notable changes to the diet since publication?


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  6. I love this thread but don’t have time to read every comment. Thank you for your research and work! I was brought here because I have been strict keto for 3 months and my eyes are watering all the time and I am dehydrated for sure. I see that you say glucose will cure them… some white rice. My question is how can I eat white rice and still lose weight on keto? I have alot to lose. If I cheat at all(which i purposefully do about once a month) I gain about 6-8 pounds almost immediately and it takes me about 7 days to lose it. I just cant afford that kind of aggravation. Of all the comments I read, no one referred to needing to lose weight. I am just wondering how can I cure my dry eyes while staying on keto? Is that possible? Would getting out of dehydration by supplementing magnesium and potassium and more water do the trick? Adding vitamin c? Do I have to add in glucose and if so then how do I do that and still remain in ketosis? Please assist. Thank you.

    • How Do You Eat a Ketogenic Diet?

      The safest and healthiest way to eat a ketogenic diet is by:

      Restricting carbohydrate consumption to 200 calories per day from “safe starches” like rice, taro, and sweet potatoes. 70 grams of cooked white rice, 150 grams of taro, and 300 grams of sweet potato are an appropriate daily ration.
      Eating massive amounts of coconut oil. The short-chain fats in coconut oil are the most “ketogenic” of foods, i.e. the most readily turned into ketone bodies. 6 to 8 fluid ounces (12 to 14 tablespoons) per day of coconut oil is an appropriate daily ration.
      Supplements with vitamin C and selenium should also be increased on a ketogenic diet.
      —-the above is Paul writing on his blog years ago.
      I will add that he doesn’t say it here but clearly states that carb calories + protein calories should be at least 600. So you need minimum of 400 protein calories with 200 carb calories. When I want to loose weight I eat mostly fish and egg yolks for my protein. Shrimp, cod, pollock, mostly since they are low fat, and 8-12 ounces of salmon or sardines per week for omega 3 (even though they are fattier). The intent is to avoid the dangers of inadequate glucose (200 calories of starch with 400 calories of protein seems to be a sweet spot where you can generate keystones from the short chain fats).

      I would be worried about starving yourself below these minimums. Your body might be desperately rebuilding structures it can’t maintain on very low carb levels, only to have them torn down again when you stop “cheating”. The weight loss version of PHD WORKED WELL FOR ME. Eating mostly fish, potatoes, low cal veg and not too much extra fat. Maybe at least 2 tbsp coconut oil, and maybe you take that at the end of the 16 hour daily fast. Broccoli, onion, snow peas, 5-6 ounces of fish, 5-6 ounces of potato or 4 ounces of rice. And walk 20 minutes before breakfast. The low cal fish let’s you get a lot of nutrition with little fat so your body will start using your body fat for it’s needs. The coconut oil will be converted to ketones even with the carb and protein.

      • After posting this I realize I wasn’t clear: those rough measures were per meal. But I’ve found Paul’s 4 quadrant rule of thumb is easy and effective. Divide your plate into 4 quarters. Each meal eat a roughly equal amount of fish, starch (potatoes are best, previously steamed and refrigerated, chopped and warmed in coconut oil or butter), low cal veg (cucumbers with rice vinegar and salt, broccoli, cauliflower…) and a sweet plant (berries, beets, carrots). Experiment until you find the amount that is enough for you so that you are only barely getting hungry after fasting 16 hours daily. Eat in an 8 hour window, either 2 or three meals, and enough that you are never hungry.

  7. Why not fruit?

  8. I would’ve liked to have seen the author raise his fat intake instead of his carbohydrate intake to see if this helped with his dry eyes. There’s a reason that there’s no such thing as essential sugars or essential carbohydrates. If after raising his fat intake he still had dry eyes and other symptoms then by all means increase your carb intake but I think that a higher fat low to zero carb diet could be the answer. Even Vilhjalmur Stefansson said that when he was being observed eating an all meat diet that he felt ill and had more issues when the meat he at wasn’t fatty enough. Same with hunters and explorers that had rabbit as their main source of fuel, the rabbit meat was so lean that they lost muscle mass and had very low energy because their bodies had to use the protein in their muscles for fuel because the rabbit meat was to lean.

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  10. Soxmany holes in this analysis, where to begin. What about people who look and feel great after cutting carbs?

  11. Hello,

    In your opinion, how long could it take to recover from dry eyes/nose after a strict keto for almost one year? I eat 130 grams of carbs (whole rice) since one week, but only the mouth recovered 🙁


    • Hi Tardi,

      It shouldn’t take long. A few weeks if you are obtaining all the nutrients you need. Make sure you take vitamin C and get other things that may also have become depleted on keto.

      Best, Paul

  12. Dear Paul,

    can excessive fat intake increase the need for carbohydrates?
    Can this cause a lack of carbohydrates or an increased need for carbohydrates?

    Best regards


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