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There Is No Single Cause of (Or Treatment For) Obesity


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One of the most hotly debated subjects over the past few years has been the cause of the obesity epidemic, and along with that, the best strategy for weight loss.

Some folks (Atkins, Taubes, Eades, etc.) believe that carbohydrates are to blame. Others (Ornish, Campbell, Esselstyn, Fuhrman, etc.) believe that fat is the problem. More recently, researchers like Seth Roberts and Stephan Guyenet and clinicians like Dr. Sharma have raised awareness of another hypothesis, called the food reward theory, which holds that the consumption of highly palatable foods leads to overeating and weight gain. And Paul Jaminet and others have argued that micronutrient deficiencies, toxins and infections may play a significant role in the obesity epidemic.

Here’s what I think: the most accurate answer to “why do people get fat?” and “what’s the most effective weight loss strategy?” is: “it depends.”

Separating Cause from Mechanism and Effect

One of the biggest mistakes often made in this debate is the confounding of cause, mechanism and effect. A classic example is the assumption that if reducing carbohydrate or fat intake leads to weight loss, then the original weight gain must have been caused by excess carbohydrate or fat consumption.

While it’s tempting to make such an assumption, the logic is faulty. It’s kind of like saying “Advil cures headaches. Therefore, headaches must be caused by Advil deficiency.”

Let’s look at some definitions.

Cause: something that brings about an effect or a result

Mechanism: the fundamental processes involved in or responsible for an action, reaction, or other natural phenomenon

Effect: an outward sign

Obesity is an effect. Insulin resistance, leptin resistance, lipotoxicity, disruption of the mesolimbic dopamine reward pathway and inflammation of the hypothalamus are presumed mechanisms. Excess consumption of carbohydrates, fat, highly palatable food and food toxins (wheat, seed oils, liquid fructose, etc.), exposure to environmental toxins (chemicals), stress, infections, etc. are presumed causes.

Say we do a study on obese people and we observe that they eat a lot of carbohydrates and are insulin and leptin resistant. It’s easy to assume that the chain of causality worked like this: normal weight person eats high-carbohydrate diet, becomes insulin and leptin resistant, and then becomes obese.

But again, this is faulty logic. There’s no proof that A (high carbohydrate intake) was what led to B (insulin and leptin resistance) was what led to C (obesity).

In fact, we could disprove that theory simply by observing another individual or group that eats a very high carbohydrate diet, but does not develop insulin or leptin resistance and obesity. Guess what? Such individuals and groups most certainly exist. There goes that theory.

Likewise, we could also disprove this theory by observing people that are insulin and leptin resistant, but don’t become obese. Such people do exist, and I’ve written about them in my series on diabesity and metabolic syndrome.

A More Rigorous Approach

How have we developed our theories on obesity and weight regulation? It seems to me they come from a blend of personal experience, belief and facts. And I think it’s time to become more rigorous about keeping them separate. Here’s an example of what I mean:

Personal experience: I lose weight on an low-carb diet, therefore low-carb diets must be best for weight loss.

Belief: carbohydrates are responsible for the obesity epidemic, via their effects on insulin.

Fact: many cultures around the world eat high-carbohydrate diets and are exceptionally lean.

Those who’ve lost a lot of weight on a low-carb diet have a tendency to become convinced that their wife, friends, family, plumber and everyone else will also lose weight following the same diet.

From this personal experience, a belief is formed. And once we believe in something, we have a remarkable ability to filter out any evidence that might contradict that belief.

This is especially true if our reputation or financial livelihood is tied to said belief. As Upton Sinclair famously said:

It’s difficult to get a man to understand something when his salary is dependent upon him not understanding it.

When a belief like “carbs cause obesity” is shared between enough individuals, it becomes a meme. Once that happens, it is accepted by most as fact – regardless of whether it has any scientific basis. Hence we had the idea for decades that eating fat makes you fat, and now the more recent idea that eating carbs makes you fat.

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There’s No Single Cause (Or Treatment) of Obesity

Perhaps one of the reasons it’s so easy to confuse cause, mechanism and effect and personal experience, belief and fact is that obesity is an incredibly complex disease. Just how complex is it?

Click on the Obesity Systems Influence Diagram below to find out.

Click image for larger version

Wow. That should give you a rough idea of how many variables are potentially involved in weight regulation. Now you know why it has been such a challenge to come up with a single, unified theory of obesity.

That said, of all of the hypotheses advanced to explain the mechanisms behind obesity, I think the food reward theory is the most inclusive.

However, as even its proponents would agree, it doesn’t tell the whole story because there are people and groups that eat large amounts of highly palatable foods that do not become obese.

My opinion is that the modern lifestyle (i.e. food and environmental toxins, stress, poor gut health, infections, micronutrient deficiencies, sleep deprivation, etc.) interfere with hypothalamic hormonal regulation, dopamine signaling, leptin and insulin sensitivity at the cellular level, glucose metabolism and a range of other mechanisms that lead to obesity.

This is consistent with the observation that obesity is extremely rare or nonexistent in traditional cultures that do not consume modern foods and do not live a “modern” lifestyle.

But even this theory is incomplete, because there are people fully exposed to the modern lifestyle that do not become overweight or obese. This suggests that genetics, and perhaps other undiscovered factors, also play a role.

We’re Not Robots

Humans are not robots. We’re living, breathing, dynamic organisms influenced by varying genetics and environmental conditions.

Anthropological evidence combined with modern research has helped us to reveal the basic template of a species-appropriate diet. However, it has also shown us that humans can thrive on a wide variety of macronutrient ratios and foods within that basic template.

This is not a belief. It’s a fact, supported by the evidence as a whole. Ignoring the evidence doesn’t make it go away. Believing passionately in something doesn’t make it true. Experiencing something personally doesn’t make it fact for everybody else.

19th century philosopher Charles Peirce said:

The state of belief is a calm and satisfactory state which we do not wish to avoid, or to change to a belief in anything else.

And Tolstoy said:

I know that most men, including those at ease with problems of the greatest complexity, can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread, into the fabric of their lives.

Recognizing this basic human trait, philosopher of science Karl Popper advised every researcher to earnestly try to discredit their own hypotheses.

That is no easy task, and it asks a lot of us. Yet intellectual rigor, emotional maturity and personal integrity are characterized by the capacity to question our own beliefs, no matter how deeply cherished they are or how much is at stake.

I sometimes wonder why we’re all so sure of ourselves. It helps me to remember that at every point in history scientists (and the general public) were convinced they had the right answers. At one time the world was flat, the earth was the center of the solar system and disease was caused by foul humors and could be cured by bloodletting.

Nowadays we look back on those fallacies with a smirk. But are we so arrogant to assume that our great-grandchildren won’t do the same?

The truth is, there’s far more we don’t know than we do know.

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Join the conversation

  1. If there were a thunderous applause icon I’d be using it right now! You echoed my sentiments exactly, especially in the last paragraph! Thank-you, thank-you, thank-you!

  2. You know, while I agree in general with the message, I don’t actually agree with the title- Because there is a simple way for anyone without a legitimate medical condition to lose weight.

    Eat less and work out.

    The problem isn’t that we don’t know how to get into better shape and better health- It’s that a lot of the people who suffer from obesity find it too difficult to put the work in to change their lifestyles and become more active and healthy.

    There’s also a lot of coddling around the subject- “It’s fine if you’re fat, so long as you’re happy,” “You’re beautiful -because- of your corpulence,” etc. This is blantantly untrue- Being fat is not healthy or attractive- but we still tell people it’s fine because we’d rather let them kill themselves through complacency and consumption than make them feel bad.

    This isn’t a popular opinion- But I’d rather hurt someone’s feelings than let them kill themselves slowly. Perhaps that’s just me.

    • You as the clueless person who has not dieted and exercised ad nauseum and had it have very little effect in the end have no idea what you are talking about.
      I would love it if it were this simple but for many it’s not. When I diet it just makes me so much worse. I’m not even a big eater or a bad eater. No processed foods and generally no more than 2000 calories a day. What happens to me if I try to eat by my brain and impose restrictions on calories or macronutrients like carbs or fat is that I get weird symptoms like cold hands and feet, fatigue and insomnia at night. Hypo metabolic symptoms basically.
      I just had testing done and found that my cortisol and dhea production is through the roof. I have a history of abuse and PTSD, antibiotic overuse yeast infections and colitis. There is a lot of emerging evidence that weight gain can be the result of antibiotics and resulting inflammation from disruption of gut flora and infections it causes.
      The result for me of dieting or strenuous exercise is exhaustion to the point of being bedridden and raging insomnia. I’m sure it’s because it aggravates even more excess cortisol because it’s more added stress my body can’t take. It really sucks.
      It is so infuriating to have clueless people like you accusing everyone who can’t lose weight and who seem to slowly gain no matter what they do of just being lazy gluttons. What arrogant tools you are.

  3. Respectfully, I think you’re using a lot of faulty logic here. First, it doesn’t matter that some people can consume high levels of carbohydrates and not get fat when discussing the causes of fat gain. However, this group can be helpful in understanding the causal mechanisms. Yes, people are different and therefore their bodies will react differently under different scenarios. However, while not everyone who consumes excessive carbohydrates (>100g/day) has a high body fat percentage, EVERYBODY with a high body fat percentage got that way while consuming excessive carbohydrates. Bottom line: You’re confusing “cause” and “causal mechanisms”.

    Second, you assume that the reverse logic of the hypothesis (consuming excessive carbs increases body fat %) must be true. In other words, you insinuate that carb restriction must result in fat loss in order for the hypothesis to be true. However, this logic doesn’t account for the possibility that consuming excessive carbohydrates might cause irreversible damage to a body’s ideal state. Such damage (thyroid issues for example) can make losing body fat near impossible. However, that doesn’t negate the hypothesis.

    Bottom line: EVERY person with high body fat percentage got that way while consuming in excess of 100 grams of carbohydrates per day.

    • Kennen,

      Well-stated logic.

      However, please cite your final assertion.

      It seems to me that fats are a major issue, but are not carbs, and glycemic index (GI) of food has a lot to do with modern obesity, maybe even more than carbs in general. Given those two issues, saying EVERY, strikes me as hyperbole. It seems to me, that someone who eats lots of fatty meats and lots of salads drowned in high-fat salad dressings (even if they are sugar free), and consumes fewer than 100 grams of carbs, but the ones consumed are high GI (like drinking some Gatorade) could still get a high body fat percentage.

      Yes, that kind of diet would be odd, but it is a modern oddity, brought on by the fear of carbs.

      My point is, without citation of the word EVERY, it seems conceivable that there could be exceptions to your assertion. But if your assertion can be cited, I would be highly motivated to read the citation(s).

  4. excellent article.
    i think that obesity is really one of those things were lots of people (including scientists) are so convinced they ‘have it figured out’ that they will go very far to block out any data that does not fit with their own conclusions.
    i always felt that the notion of obesity as ‘your own fault’ plays a very large role in this: people like looking down on other people (‘he is a lazy slob who should just eat less/healthier/a particular kind of food’) and hate being looked down upon themselves (‘my weight is not caused by me being a lazy slob’)

  5. EXCELLENT article, Chris. I just saw this now. It is very true that the unknowns about obesity are far greater than the knowns.

    One of the knowns is that the genetic component of obesity is almost equal to that of height ( and possibly equalling it) , as Dr. Jeffrey Friedman has demonstrated. he is one of the foremost experts on obesity in the world- a true genius.

    The good scientists always admit there are many things that we do not understand about our body’s weight regulation systems that make long term weight loss exceddingly difficult. Dr. Linda Bacon and Dr. Jeffey Friedman are great.

    Here is a VERY extensive review of the literature on weight management, none of which supports the popular media view :


    Thanks for adressing obesity.

    Take care,

  6. In regards to Jason’s Inquiry “Are there any cultures that become obese without a large intake in added sugars and/or wheat?”

    How about native Hawaiians before Europeans came to the islands? They wanted their royalty to be extremely fat, but they managed to be very fat without grains or refined sugars. Diets were primarily pig, seafood and fish,fiberous vegetables, starches (taro, breadfruit, etc), coconut and fruit. How did the alii get so fat????

  7. Perhaps it is chronic high-carb intake that is a culprit? According to T.S. Wiley (author of Lights Outs: Sleep, Sugar, Survival) when we’re eating high-carb throughout the year, that tells our body we are in perpetual summer, which ages us 4x faster. Wiley even says that the reason Atkins doesn’t work long term is because it’s chronic low-carb (apparently the two were friends and Atkins asked her why his diet stopped working). Chronic anything might be bad for us.

    Our ancestors had to eat what was in season. Summer allows for more carbs, winter allows for mostly animal food.

  8. After having been a collegiate level athlete and graduating college eating the same amount and combination of food with little to no exercise, I gained 70 pounds. I realized my mistake and took my food intake down and my exercise up. I have successfully lost the 70 pounds plus more. I eat mostly healthy foods with the occasional pizza or burger, and try to make fresh foods for meals rather than using packaged. All that said, this is what worked for me specifically, true, but I think your sole focus on food intake is not correct. Our culture slowly throughout the 20th century became a culture of instant or very fast gratification, with processed foods but mostly in the way we live our lives by means of working our bodies. We drive cars, sit at desks, stare at television screens, and we forget that our grandparents or their grandparents did not have this kind of lifestyle. Yes we should look at food, but we should also ask ourselves if we are exercising our bodies enough to warrant the amount of food we consume. Moderation is key.

  9. I read the Shangrila Diet and it had a really interesting take on food palatability, the complexity of which seems to be totally lost in the “eat bland food” recommendations. In fact, experimenting and trying out new foods was a recommended part of the plan, as the body doesn’t trust new flavours in the same way that it likes and remembers and craves comfort food. This is kind of the French Women don’t Get Fat concept. And interestingly, the author was in france when he came up with the idea.

    Also, bland food eaten to promote weight loss, had to be completely tasteless and kept free from all flavour for an hour on either side to avoid associations with it, as these associatons are learned and change over time.
    And another thing, “palatable” and “delicious” don’t mean exactly the same thing. (Remember the macdonald’s burgers with dijon and how they had to sell them as “adult” because their audience can’t stand any kind of flavour). All of the bland but high calorie food at macdonalds gets associated with specific strong flavours such as the coke and ketchup, but in general the food is generic and tasteless. It’s more about the texture and how it chews easy and goes down easy. They spend fortunes figuring out how to make all of the food form a bolus quickly so it’s swallowed quickly. It’s like baby food. It’s not gourmet food with complex flavours and texture. And it’s exactly the same everytime, so it’s extra easy to swallow. I recently ordered a bunch of unknown dishes at a japanese restaurant, and there’s nothing like that to realize how slowly one can eat when the food is new to you, compared to how quickly a familiar fast food goes down.
    Anyway, I am butchering the book and the concepts, but reading that eating chicken breast and rice with no flavourings is the way to lose weight is so …. lame! specially as you will probably learn to associate even that amount of flavour with calories, and then what do you do? there isn’t anything blander!
    I personally think that palatbility is an interesting concept but I think malnutrition in spite of high calorie intake has to be part of it too, and triggering any kind of starvation response, even with a low carb paleo, is disastrous. I recently was on the gaps protocol and was doing good and then had a couple of days where I under ate and wham! I was waking up with anxiety and my heart going crazy, and starving and gaining weight no matter what I ate. I dealt with it by just eating a lot of good food, as much as I could but kept it all paleo, until everything calmed down. About a week of eating 4 meals a day and then suddenly one day it all felt like too much food. Gained a couple of pounds, but now settling back down into weight loss.

  10. Good post, much like Chris Masterjohn’s today. So…..this all seems to be bring us back to…where was that again?

    Anyway, I’ve decided to follow my grandmothers advice (which sounds a lot like Michael Pollan’s): Eat when you’re hungry, don’t eat seconds, don’t snack, don’t eat too many deserts. Tempered by eat real food, mostly plants.

  11. I’ve yet to see the “whole foods diet and resistance exercise” fail in this respect. In our 20th century world where carbs come from wheat and fructose along with fats derived from seed oils and corn or soy fed animals, it’s no wonder entire macronutrient groups became demonized. Of course there’s no single treatment for obesity. That’s because there’s no single cause for it either.

    • It failed me. I eat no processed anything.

      I think my gut is messed up and that is where the problem lies. I just had a test and my cortisol is half again more than the top of the normal range. I’m obviously having a major stress response to something.

      My gut was never right. Fed formula I couldn’t digest and constantly puked and cried and so constipated as a child I screamed to go to the bathroom topped off by loads of antibiotics and birth control pills. I was very sick as a child.

      My weight problem has been in phases. I was skinny til a few years after my tonsils were removed at 4. Then I was a bit chunky but not really fat by any means. Then I leaned out in puberty and adolescence only to start gaining in between pregnancies but I lost it all after my three kids were born about two years apart in my late twenties early thirties. But then I moved to a house that had mold and got very sick about 10’years ago and I gained and gained and have this cortisol flood I just found out about. I have to be so careful not to add stressors, dieting hard exercise problem people etc or I can’t get out of bed from exhaustion and can’t sleep from the high night cortisol.

  12. This is fascinating stuff! I think the point that everyone is missing but which is hinted at nicely in the article is the principle of individuality. Everyone is different. What works for one person will not necessarily hold true for another (“one man’s food is another man’s poison”).

    Whilst high protein / fat and low carb works well for many people, there is no, ‘one size fits all’ prescription for health and optimal body composition. Some people just thrive on carbs and can’t tolerate high protein and fat diets. Eating like this won’t make them obese. This individual variation is the basic principle of metabolic typing.

    Another thing is that people don’t distinguish between ‘good’ carbs and ‘bad’ carbs ie. natural, vegetable based carbs vs. refined carbs. This is an important point. So, the problem never was carbohydrates (the blanket term) per se.


  13. Great article! I read this as a response to the Stephan / Taubes battle that emerged from the AHS???