The top 3 dietary causes of obesity & diabetes

donutSo far in this series 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.

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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  1. TimL’s avatar

    Regarding the toxicity of fructose, are you recommending any specific limit on fruit intake? Or is it primarily HFCS and refined sugar we have to worry about?

  2. Chris Kresser’s avatar

    Fructose is fructose, and is processed in the same way whether from HFCS or fruit.  So yes, I do recommend limiting fruit intake to about 2 servings per day as a general rule.

  3. woly’s avatar

    I think it was Eades who said that he wasnt too concerned about HFCS specifically (as opposed to sugar in general) since it is only 5% more fructose than glucose. What is your opinion on this?

  4. Chris Kresser’s avatar

    Of course they’re both best avoided.  But the threshold for fructose toxicity is so low, that it make sense to do everything we can to avoid excess amounts.  5% may not be a large difference, but in the context of 150 pounds a year of sugar (the average American’s intake), it’s not insignificant.

  5. Ann’s avatar

    Chris, Your answer on the 5% more fructose in HFCS question seems too important to hide in the comments–especially with the current ad campaign to shift the label to “corn sugar.” In addition, there are the issues of trace amounts of mercury from processing corn into HFCS and the consumption of GMO corn via this pathway. A new post that investigates the specific harm of HFCS (versus fructose in general) might be helpful for folks who are feeling persuaded that HFCS is no different from sugar.

  6. kb’s avatar

    How can you compare the fructose in HFCS to that in fruit—-and suggest that fruit could possibly be as toxic as HFCS?!  I am appalled at this.  Have you even seen the incredible health of Fruitarians?  Their body habitus certainly doesn’t support your suggestions that the fructose in fruit is even remotely as dangerous as the chemically engineered product called HFCS.  There is a HUGE difference because the sugar in fruit is just a PART of the entire package—which is why eating fruits and vegetables over grains and other crap is so much better for a body.  Take away grains 100% and ONLY eat fruits, veggies and meats and you can pretty much cure the human body of all diabesity—even eating pounds of fruit a day!

  7. Chris Kresser’s avatar

    I didn’t say fruit is the same as HFCS.  I said fructose is fructose.  It’s the same molecule. And fructose gets processed by the liver in the same way, whether it comes from HFCS or fruit.  Of course HFCS is a toxic, highly refined and processed product, and fruit is natural. But that doesn’t mean we can eat as much as we want of it and function optimally.  Humans did not have the kind of access we have to fruit now – especially the sweeter fruits – until relatively recently on the scale of evolution.  We are not adapted to eat unlimited amounts of it – the way the liver processes fructose is proof of that.  I’ve worked with several people that on a strict paleo diet, and still have symptoms because they’re eating too much fruit.  When they reduce the fruit, the symptoms (and their blood sugar) abate.  So while I agree that eliminating grains is ultimately more important than moderating fruit intake, I certainly don’t agree that eating pounds of fruit a day is advisable for anyone.

  8. java’s avatar

    I would definitely like to respond to this one above. I believe that ultimately it all depends on your genes and other markers. I have not eaten any grain for the past few years. PUFA consumption is limited to occassional meals eaten in restaurants or elsewhere and sugar is something I dont touch,except for exactly one piece of chocolate once a week. Up until a few months ago [to be precise, till I saw Dr. Robert Lustig video] I ate plenty of fruit. Definitely two a day.I ended up with a fatty liver. Ever since I have given up eating as much fruit [I eat one fruit serving a week now], my fatty liver has cleared up.So I beg to differ and dont believe anyone who says fruit is safe just because it is natural. In the end,everything is natural…..grains are natural too,and ultimately all drugs are also natural.I agree with Chris that whichever way you look at it ,it is the same molecule. Remember the downfall of Adam was afterall the apple in the Garde of Eden.

  9. kevin’s avatar

    some fruit i wouldnt consider natural in my opinion….. But i really depends how you want to define natural….Banannas as we know them have only been around for 200 years or so.  They are a mutant that came out of a plantation of red and green cooking banannas.  Not that they are 100% bad…but i have seen some “fruitarians” eat banannas to the point where they got gout.   Everything in moderation..  I think people just eat too much in general….on top of that they eat crap….so the process is sped up.  Paleo all the way.  You would never find fruit often in natural.  Green veges mostly and an occasional animal if you are lucky.  Or you would be herding and foraging.  I met a masai warrior this past weekend.  He ate nothing but blood and milk till the age of 15 and looks better than some fruitarians i have seen.   The point is to eat natural diet and stay active.  35 bananas in one sitting is just digusting.  That is gluttony. Doesnt matter if its a 2 litter bottle of coke or 35 bananans its still too damn much for the body to handle.

  10. sandy’s avatar

    @ java….I am curious was your fruit Organic? Thanks

  11. Bryan - oz4caster’s avatar

    Another great post Chris!  My guess would be that when it comes to cereal grains, it’s primarily the glutenous grains that are most suspect in contributing to diabecity.  It’s the gluten that causes gut damage and inflammation. I’m not so sure rice is much to blame and maize may also be less of a problem.  I have read that rice bran may cause digestive problems, but white rice does not.  Also, I’ve read that long sourdough fermentation of a day or more may break down gluten so that it is less likely to cause problems.  Likewise, proper preparation of maize by nixtamalization makes it more nutritious and digestible.  Of course, I realize that most modern cereal foods are not prepared properly, with the possible exception of white rice.  Just some food for thought :)

  12. Jesse’s avatar

    So you’re saying that, because cereal grains were so unhealthy, our ancestors before 10,000 years ago didn’t eat them. Why did they start eating them at all then, and how did they survive all this time eating such poisonous food?

  13. Chris Kresser’s avatar

    I agree that white rice isn’t problematic for most people, and I eat it myself in small quantities.  Corn I’m less certain of.  It’s a common allergen, and it can cause pellagra in large quantities.  Nevertheless, I do believe that gluten is the main culprit.

  14. Chris Kresser’s avatar

    Jesse: read the two links at the end of the cereal grains section.  They will answer your questions.

    It’s not a question of survival.  It’s a question of optimal health.  And yes, our paleolithic ancestors didn’t suffer from the chronic, modern diseases that plague us today.  Their average lifespan was shorter because of accidents, infant mortality and violent death, but their overall health was superior.

  15. JB’s avatar

    Chris: I believe the same thing about why the average lifespan used to be shorter (“accidents, infant mortality and violent death”) but was wondering if you have any resources to back that up? I have friends who believe there was just as much cancer, diabetes, heart disease, etc. in the past. They believe that 1) people didn’t live long enough to develop some of the diseases (i.e. they believe these are age related diseases), and 2) they believe the medical community in the past didn’t have a way to diagnose these conditions. How can I prove them wrong?

  16. Chris Kresser’s avatar

    JB: Here’s one resource.

  17. kb’s avatar

    I still don’t buy that fruit, in it’s natural state is as bad as you and others are saying.  Please link me studies and information to prove this.  I would bet that fruit ALONE could not cause the fatty liver etc.  There simply HAVE to be other factors contributing.

  18. kb’s avatar

    I have also sent an inquiry to Dr. Doug Graham of FoodnSport and the Fruitarian 80/10/10 diet and let him know your take on how harmful fruit is.  Simply because I just find it impossible to believe that eating fruit, along with lots of veggies and good meats could cause one to be the unhealthy, fat pigs that many Americans are—with fatty liver and all.  I just find it unbelievable that you could even give this advice.  Fruit will ALWAYS be better than ANY packaged crap, baked crap or grain.

  19. Chris Kresser’s avatar

    Fructose is fructose.  It is processed in the same way, regardless of where it comes from. That’s a fact, and it’s not controversial.

    If we were meant to consume fructose in large amounts, then the body wouldn’t treat it as a toxin (i.e. shunt directly to the liver and store as fat to remove it from circulation). Glucose is an entirely different story, since it’s rapidly absorbed into the bloodstream and is a critical ingredient in energy production (ATP).  We can live without fructose, but we can’t live without glucose.

    Once again, I am not saying fruit is “bad”.  As I said in the article, anything can be toxic at high doses – including water.  Our ancestors didn’t have the kind of access to fruit that we have today.  It was largely seasonal, and they weren’t growing it themselves on huge plots of land.  The fructose content of paleolithic fruit was also much lower than the varieties we have today (which have been selected for sweetness over many generations).

  20. Chris Kresser’s avatar

    I did not say that fruit is more harmful than packaged food or grains.  Nor did I say that fruit is responsible for the epidemic of fatty liver disease.  Clearly HFCS is the primary culprit.  But that doesn’t mean that people can eat unlimited amounts of fruit without adverse effects. If you understand how fructose is processed, this should be clear.

  21. kb’s avatar

    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.

  22. Tracee’s avatar

    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.

  23. Jesse’s avatar

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

  24. Jesse’s avatar

    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.

  25. Kurt G Harris MD’s avatar

    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”.

  26. Chris Kresser’s avatar

    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.

  27. Kurt G Harris MD’s avatar

    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.

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