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The Top 3 Dietary Causes of Obesity & Diabetes


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So far in this series on diabesity and metabolic syndrome, we’ve focused on a new way of understanding diabesity as an autoimmune, inflammatory disorder, and we’ve looked in a general way at the underlying mechanisms (inflammation, genetics, environmental triggers and leaky gut) that contribute to diabesity.

Now that we’ve laid that foundation, we’re going to take a closer look at some of those mechanisms. In this article, we’ll discuss the three major dietary toxins that trigger diabesity:

  • Cereal grains (especially refined flour)
  • Omega-6 industrial seed oils (corn, cottonseed, safflower, soybean, etc.)
  • Fructose (especially high-fructose corn syrup)

At the simplest level, a toxin is something capable of causing disease or damaging tissue when it enters the body. When most people hear the word “toxin”, they think of chemicals like pesticides, heavy metals or other industrial pollutants. But even beneficial nutrients like water, which are necessary to sustain life, are toxic at high doses.

In the Perfect Health Diet, Paul & Shou-Ching Jaminet apply the economic principle of declining marginal benefits to toxins:

It implies that the first bit eaten of any toxin has low toxicity. Each additional bit is slightly more toxic than the bit before. At higher doses, the toxicity of each bit continues to increase, so that the toxin is increasingly poisonous.

This is important to understand as we discuss the role of each of the dietary toxins listed above in contributing to diabesity. Most of you won’t develop diabesity by eating a small amount of fructose, cereal grains and even industrial seed oils. But if you eat those nutrients (or rather anti-nutrients) in excessive quantities, your risk of diabesity rises significantly. This is especially true if you have any of the genes that predispose you to diabetes and obesity.

The primary effect toxins have on the body – whether dietary or otherwise – is inflammation. And since we now know that diabesity is an autoimmune, inflammatory disease, it’s clear that anything that causes inflammation is a potential risk factor for both diabetes and obesity.

The impact of each of these dietary toxins could fill a book. And in fact, there are several such books and many other blogs that have covered this material in detail. Rather than re-create the wheel, I’m going to provide a brief summary and then link you to resources if you want more detail.

Cereal Grains: The Unhealthiest “Health Food” on the Planet?

The major cereal grains – wheat, corn, rice, barley, sorghum, oats, rye and millet – have become the staple crops of the modern human diet. They’ve also become the “poster children” of the low-fat, high-carbohydrate diet promoted by organizations like the American Heart Association (AHA) and American Diabetes Association (ADA).

If you say the phrase “whole grains” to most people, the first word that probably comes to their mind is “healthy”.

But the fact is that most animals, including our closest relative (the chimpanzee) aren’t adapted to eating cereal grains and don’t eat them in large quantities. And humans have only been eating them for the past 10,000 years (a tiny blip of time on the scale of evolution). Why?

Because plants like cereal grains are always competing against predators (like us) for survival. Unlike animals, plants can’t run away from us when we decide to eat them. They had to evolve other mechanisms for protecting themselves. These include:

  • producing toxins that damage the lining of the gut;
  • producing toxins that bind essential minerals, making them unavailable to the body; and,
  • producing toxins that inhibit digestion and absorption of other essential nutrients, including protein.

One of these toxic compounds is the protein gluten, which is present in wheat and many of the other most commonly eaten cereal grains. In short, gluten damages the intestine and makes it leaky. As we saw in the last article, a leaky gut is one of the major predisposing factors for diabetes and obesity.

Celiac disease – a condition of severe gluten intolerance – has been well known for decades. These people have a dramatic and, in some cases, potentially fatal immune response to even the smallest amounts of gluten. However, what is less well known is that wheat gluten triggers an immune response and gut inflammation in almost everyone – regardless of whether they are “gluten intolerant” or not. Over 80% of the population develops measurable gut inflammation after eating wheat gluten.

Dr. Kurt Harris, author of one of my favorite blogs (PaleoNu), calls wheat one of the three “neolithic agents of disease” (we agree on the other two as well). For more information on the toxic effect of cereal grains, see Dr. Harris’s two articles “The argument against cereal grains” and “The argument against cereal grains, part II”.

Industrial Seed Oils: Unnatural and Unfit for Human Consumption

Industrial seed oils (corn, cottonseed, soybean, safflower, sunflower, etc.) have not been a part of the human diet up until relatively recently, when misguided groups like the AHA and the ADA started promoting them as “heart-healthy” alternatives to saturated fat.

The graph below shows how dramatically seed oil consumption has risen over the past several decades:


Industrial seed oils are extremely harmful when consumed in excess. I’ve written about this at length in my series on essential fatty acids. In the context of this article, researchers have shown that industrial seed oils have played a significant role in the current obesity epidemic.

A recent study showed that a diet with an omega-6:3 ratio of 28 (meaning 28 times more omega-6 than omega-3 fats) caused obesity that progressively increased over four generations of mice. This means that eating too much omega-6 didn’t only cause obesity in the current generation, but it also predisposed future generations eating the same diet to developing obesity.

This is bad news for those eating a Standard American Diet, which contains an omega-6:3 ratio that is very similar to what the mice in the study above were fed.

Omega-6 seed oils have also been shown to cause inflammation, insulin resistance and impaired leptin signaling, all of which directly contribute to diabetes.

Finally, industrial seed oils have been shown to interfere with thyroid function by blocking the binding of thyroid hormone to its receptors. The result is a higher fat mass and a less efficient metabolism.

For more information on how seed oils contribute to diabesity, see The Body Fat Setpoint, Part III: Dietary Causes of Obesity, Have Seed Oils Caused a Multi-Generational Obesity Epidemic?, and my series on Essential Fatty Acids.

Fructose: The Sweetest Way to Get Diabesity

White table sugar is composed of two sugars: glucose and fructose. Glucose is an important nutrient in our bodies and is healthy, as long as it’s consumed in moderation. Fructose is a different story.

Fructose is found primarily in fruits and vegetables, and sweeteners like sugar and high-fructose corn syrup (HFCS). A recent USDA report found that the average American eats 152 pounds of sugar each year, including almost 64 pounds of HFCS.

Unlike glucose, which is rapidly absorbed into the bloodstream and taken up by the cells, fructose is shunted directly to the liver where it is converted to fat.

Excess fructose consumption causes a condition called non-alcoholic fatty liver disease (NAFLD), which is directly linked to both diabetes and obesity.

A 2009 study showed that shifting 25% of dietary calories from glucose to fructose caused a 4-fold increase in abdominal fat. Abdominal fat is an independent predictor of insulin sensitivity, impaired glucose tolerance, high blood pressure and high cholesterol and triglycerides.

In a widely popular talk on YouTube, Dr. Robert H. Lustig explains that fructose has all of the qualities of a poison. It causes damage, provides no benefit and is sent directly to the liver to be detoxified so that it doesn’t harm the body.

Another danger of fructose is that it reacts with polyunsaturated fats and proteins to form toxic compounds called Advanced Glycation End-Products (AGEs) in a process known as “fructation”. (Who comes up with these words?) AGEs wreak all kinds of havoc on the body; they damage DNA, speed up the aging process and cause high blood pressure and kidney disease. And studies have shown that fructose is up to 10 times more likely to produce AGEs than glucose.

For more on the toxic effects of fructose, see The Perfect Health Diet and Robert Lustig’s YouTube talk: Sugar, The Bitter Truth.

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A Toxin-Free Diet Prevents and Even Reverses Diabetes

In addition to all of the evidence above, we have two other lines of evidence that strongly indicate that cereal grains, seed oils and fructose contribute to diabesity.

First, diabesity is either non-existent or extremely rare in hunter-gatherer cultures that don’t consume these toxic foods.

Second, two studies have shown that a paleolithic diet (free of cereal grains, seed oils and excessive fructose) produced dramatic improvements in cardiovascular and metabolic markers.

The first study, performed by Dr. Staffan Lindeberg and colleagues, found that a paleolithic diet was superior to the mediterranean diet in several ways. These are summarized in Stephan Guyenet’s article on Lindeberg’s study:

  • Greater fat loss in the the midsection and a trend toward greater weight loss
  • Greater voluntary reduction in caloric intake (total intake paleo= 1,344 kcal; Med= 1,795)
  • A remarkable improvement in glucose tolerance that did not occur significantly in the Mediterranean group
  • A decrease in fasting glucose
  • An increase in insulin sensitivity (HOMA-IR)

The most remarkable outcome of the study is that, although 12 of 14 participants had elevated fasting blood sugar at the beginning of the trial, every single participant had normal fasting blood sugar at the end of the trial.

Dr. Lindeberg published a follow-up study in 2009. In this case they compared a paleolithic diet with a conventional ADA low-fat “diabetes diet”. While the results weren’t quite as impressive as the first one, they were still very encouraging. Participants in the paleolithic group:

  • Reduced HbA1c more than the diabetes diet (a measure of average blood glucose)
  • Reduced weight, BMI and waist circumference more than the diabetes diet
  • Lowered blood pressure more than the diabetes diet
  • Reduced triglycerides more than the diabetes diet
  • Increased HDL more than the diabetes diet

At the end of the trial, 8 out of 13 patents still had diabetic blood glucose levels. However, in this study the patients had well-established diabetes for an average of 9 years. Over time diabetes progresses to beta cell destruction, which reduces insulin output. Once this point has been reached, dietary changes can be helpful but cannot completely reverse diabetes.

What this means, of course, is that the earlier you remove these toxins from your diet, the better chance you have of preventing and even reversing diabesity. And while a paleolithic diet may not reverse diabetes in those that have had it for several years, it still produces significant improvements.

** A donut is the perfect diabesity food. It’s got refined flour (cereal grains), industrial seed oils (plus trans fats for an added bonus), and plenty of high-fructose corn syrup.

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Join the conversation

  1. Both groups improved, with the paleo group improving more. The question is always “where were these study participants coming from” in terms of diet. Usually the Standard American Diet is the answer. We don’t know if Lindeberg’s group would have improved even more by limiting fruit intake and emphasizing saturated fat (I suspect they would have).

    Ultimately, I don’t believe a moderate amount of fruit is a problem for people with healthy metabolisms, as I’ve stated in the comments. I do have patients that can’t tolerate even a piece of fruit without their blood sugar spiking over 140 mg/dL, which is the danger zone. So as usual, the answer to “is fruit okay” is “it depends”.

  2. In the Lindeberg’s paper fruits consumption was 493 ± 335 per day in the Paleolithic group and 252 ± 179 grams in the Consensus group.


    Too short a duration, perhaps? If so, that would perhaps explain why in a consequent study on diabetics, averaging 8 years from diagnosis, the results were less flattering? Lindeberg further stresses the nada effect in his brand new book (2010).

    I’d love to hear your thoughts. I for one would not consider Lindeberg’s paleo version as the automatically best one out there.

  3. Hi Chris, I enjoyed your briefing here.

    However, I’ve seen you referenced Linedeberg’s paleo trials as a proof on healthiness of your recommendations. Lindeberg did not see any association whatsoever with fruit / or fructose take and health markers in his trials. What would you see as the reason of this ?

  4. Thanks so much for that quick response! I really commend you for the research you’re doing into the subject and I agree with you about most things.

    I will just add that, yes, skinny people can get diabetes (especially alcoholics!), but I said lean people who exercise regularly don’t get diabetes (they are two different populations of people). I should have made that more clear.

    I am also glad that we agree that fruits and vegetables are not bad. The culprit is a mix of factors. I have spent time working as a physician in Guatemala and the diabetes rate in rural Gautemala is astounding. They have a diet which consists largely of carbohydrates and they are sedentary – and I believe also genetically predisposed to not being able to process the high % of carbs in their diet. It is a bad combination.

    Anyway, bottom line is avoiding diabetes can be achieved by regular exercise (think nomadic lifestyle), staying lean (not skinny) and eating a balanced diet (with fats and protiens, esp. fish). An orthorexic diet, which avoids all fructose is certainly not the answer, but I don’t think you’re suggesting that either.

  5. Thanks for your comment.

    I have to disagree that people who are lean and who exercise don’t get diabetes. Please see my previous article on that subject. I do agree that they are in the minority.

    I didn’t recommend that people stop eating fruits and vegetables. I said, and the scientific literature supports me in this, that fructose is fructose – no matter where it comes from. Fructose is handled by the body as a toxic substance. It is shunted directly to the liver for processing, like other toxins (and unlike glucose or any other macronutrient), and in excess amounts it causes a host of metabolic problems.

    It’s true that corn doesn’t “cause” pellagra, as you pointed out. I didn’t word that carefully. But eating too much corn at the expense of other nutrient-dense foods containing B3 does. It’s also possible that the fructose in corn disrupts vitamin and mineral metabolism in ways we don’t fully understand yet.

    The ADA dietary recommendations (a low-fat, high-carb diet) for diabetics (by definition, people with poor glucose control) remain one of the most asinine pieces of advice ever handed out. Eating a lot of fruits and vegetables is NOT what prevents diabetes. Avoiding refined flour and industrial seed oils, along with high quantities of fructose, does.

  6. Alright – my husband just told me I had better add that I am an MD, PhD. Not that that really matters. But I do have a professional interest in the above topics and I’m not just writing to badger you.

  7. Hi Chris,

    I just ran across your blog. Thanks for gathering all of the research. It was an interesting read. I certainly agree that too much fructose in the diet is not a good thing, especially high fructorse corn syrup. But I think it is going a bit far to discourage people from eating fruits and vegetables because they contain fructose. Fruits and vegetables do not cause diabetes. Eating too much and being sedentary causes diabetes. People who are lean and exercise (and eat fruits and vegetables – or candy for that matter) don’t get diabetes (there are a few exceptions, notably Type 1 diabetes).

    I also have to doubt that fructose in and of itself is a toxin. Perhaps it could be viewed this way in people who are already overweight and/or have metabolic syndrome – in which case extra fructose won’t help anything.

    Finally, I have trouble understanding how corn could CAUSE pellagra. Pellagra is vitamin B3 (niacin) deficiency and is caused by just that- lack of vitamin B3. One would basically have to eat only corn (and no B3) for a long period of time – this is what has been seen in some poor cultures subsisting on maize alone (where pellagra has been seen). But corn doesn’t cause the defficiency.

    Anyway, don’t take my comments too personally – I commend you for initiating an interesting debate.

  8. Good question, Charles. But it’s not the same rationale. From an evolutionary perspective, the availability of sweet fruit with high fructose content was limited to certain times of the year. Also, today’s fruit is likely much sweeter than what our ancestors ate because it has been bred for for that purpose over many generations.

    Like most compounds, fructose is well-tolerated by people with healthy metabolisms in small amounts. But, in larger amounts, or in people with metabolic derangement, fructose is definitely problematic.

  9. Hi Chris,

    I love your posts and am in the process of adjusting my diet based on your writings. This is the first time I’ve heard advice to limit your fresh fruit intake (aside from the seemingly unhealthy tenets of diets like Atkins, etc.).

    I’m a bit confused though on your evolutionary argument about cereals protecting themselves with toxins from consumption by the likes of humans. This makes sense to me. But are you also saying that fruits contain toxins (fructose) to discourage us from eating them? Aren’t fruits sweet precisely to encourage us to eat them and spread their seeds? What would be the point of poisoning the vehicles on which they rely to propagate?

    Perhaps I’m confusing two different ideas but was just wondering if you have an explanation that can clear up my need to understand the logic of this.

  10. Jae: yes, that was a small study and we’ll need more research to confirm the 80% figure. However, the mechanism is plausible and well-known, and as you’re aware there are several other lines of evidence implicating gluten’s immune dysregulating properties. That’s enough to convince me it’s best avoided.

  11. I’m a bit late to the party (catching up on reading). Thanks for the excellent article, as always.

    Can you address the 80% figure that you provide for gut inflammation via gluten consumption? It looks like the sample size of that study may have been as small as 6.

    Mind you, I avoid all grains except for occasional white rice, and I’m fully on board with the idea that gluten is the most problematic of all the grains. I just want to verify if I’m reading the study correctly. I remember seeing Peter from Hyperlipid post on this a while back, but never asked him about it.


  12. I mean, for example, if you have a sucrose-sweetened soft drink, which will have more sugar in total but less fructose compared to glucose, vs. a HFCS-sweetened drink, which has less sugar but more fructose compared to glucose, is there a reason to choose one over the other?

  13. Ok thanks, that makes sense. Does it make a difference, though, that fructose is sweeter than glucose or sucrose, so you wouldn’t need to use as much of a mixture with more fructose monomer?

  14. Hey Chris,
    What is it about HFCS that is so bad that you would single it out, compared to other sweeteners (sucrose, honey, maple syrup, agave nectar, fruit juices)?

    • Fructose is worse than glucose (by far), so any sweetener that has more fructose than glucose is more detrimental. HFCS is 55% fructose and about 42% glucose, whereas sucrose is 50/50. Agave nectar is even worse. It’s fructose content ranges from 56% to 92% depending upon the source. Honey is 38% fructose. A healthy person with normal glucose tolerance can handle small amounts of this stuff, but in larger amounts or in people with deranged metabolisms they will wreak havoc.

  15. Thanks Chris
    I’ve had a busy summer and fall, transitioning into early retirement. Closing and selling various businesses, etc. I’ll have more time to blog soon, hopefully. I quite liked your thyroid series, too. Keep up the good work.

  16. Great post and great blog. Thanks for the hat tip. I first referred to wheat, fructose and linoleic acid as the “neolithic agents of disease” in an email exchange with Stephan Guyenet over a year ago. Thanks for helping spread the meme and I’d be happy to see that terminology propagated.
    I think wheat explains the existence of atherosclerosis in egyptian mummies, wheat and sugar explain the diseases of civilization introduced to aboriginal populations by the white man, and 20th century industrial seed oils added to the former the western epidemic of heart attacks and – to use your term – “diabesity”.

    • Hi Dr. Harris,

      Thanks for stopping by. I’m a big fan of your blog (I miss your articles, in fact!) I also liked your “three horsemen” term. I’ll add a reference to neolithic agents of disease to the text, right before the links to your articles.

  17. Actually, now that I think about it more…
    “Unlike animals, plants can’t run away from us when we decide to eat them. They had to evolve other mechanisms for protecting themselves.”
    By that argument, what vegetables SHOULD be healthy? Rice, carrots, spinach, broccoli, onions, potatoes, beans, celery… they should all have toxins. Almost all that’s left is fruit, except that’s no good either because it has fructose. So all that’s left is meat and other animal products. You’d think that it’d be impossible to find a healthy vegan.
    What the three things you listed have in common is that people in America eat too much of them. Eating too much of anything will make you sick. Why not simply advocate moderation?
    Though incidentally, I agree with you about seed oils.

  18. Okay, thanks. The articles you linked do seem to make more sense than what you said here, or at least Part I does.

  19. Great Article (as usual). It’s so funny you used a donut. My son was almost three when we put him on the SCD for autism. An ELISA IgG Food panel showed multiple food issues, which was actually good because we needed proof for the state. His daycare was a state certified one. We had to have a reason why he was bringing his lunch and not eating the state approved lunch. The next year he went to PPCD (special ed preschool through the local school system). The public school lunch cafeteria each week served glazed doughnuts and bearclaws to the children for breakfast. So for me, the donut symbolizes alot that’s gone wrong with our health.

    I really enjoy all your health series posts, keep it up.

  20. I guess the way you phrased the sources of fructose without clarifying that fruit—in it’s entire package—contains fiber to slow down the fructose absorption would make the average person afraid to eat fruit.  I just visited a whole host of websites offering natural treatments for fatty liver disease that recommend eating plenty of WHOLE RAW FRESH FRUITS AND VEGETABLES.  I think if you have someone with an already compromised system suffering from diabetes, obesity or fatty liver whose body needs intensive healing if not already too late, limiting overeating of ANY food product—even including lots of sweet fruits—would be important. But I don’t agree with giving this blanket (fruit has fructose, so is bad) advice to someone who already is in great health—because someone who is already healthy and eating very well with fruits, veggies and meats would be very unlikely to get obese, diabetic or fatty liver even from eating a pound of bananas a day.  What exactly is considered excessive fruit intake anyways?  I guess you would have to compare glycemic index’s of Twinkies, sodas etc. and other easily excessively consumed sugary foods with the glycemic index of whole, raw fruits—taking into consideration the built in fructose absorption altering fiber in the fruit to make the determination of just ‘how’ much fruit is ‘bad’ for a human.  My assumption would be pounds and pounds of fruit a day—which most people don’t and couldn’t tolerate anyways.

    • Fructose has nothing to do with the glycemic index. Most carbohydrates break down or convert to glucose and thus have an effect on blood glucose. Fructose is unique in that it is a 5-ring sugar that cannot be converted to glucose (which is a 6-ring sugar).

      Fructose is removed from your bloodstream by the liver, which processes it by converting it to triglycerides. The triglycerides are then released back into your bloodstream. This is what fructose DOES; it’s basic biochemistry.

      Now your body has a process called gluceogenesis that can convert protein and fat to glucose if you need it. So the specific atoms that made up fructose could eventually become glucose. But not directly, fructose is directly converted to fat.

      Whether it’s bad or not depends. If you are a hunter/gatherer trying to put on weight to make it through a lean winter, then it’s good. If you have a family history of heart disease and/or diabetes and eat too much of it, then it’s bad.

      And btw, bananas are also full of glucose… too much for me, as a diabetic, to eat as they spike bg badly. If you really, really have to eat a pound of fruit a day, I’d recommend berries instead.