A Review of “The Obesity Code”

obesity code

What’s the cause of the obesity epidemic? Why have close to 70% of the people in the U.S. become overweight or obese? Why is the state with the lowest rate of obesity currently fatter than any state was in 1980?

Many experts have tried to explain it. Possibly the most popular current theory asserts that we eat too much and don’t exercise enough. The theory is popular because it’s simple: too many calories from food results in fat storage when we don’t use them up through exercise. This is the calories in, calories out theory (CICO).

As H.L. Mencken, said, for every complex problem, there is an answer that’s clear, simple, and wrong. CICO fits this description.

Why is CICO wrong? For one thing, empirically, it doesn’t work. Diets that count on reducing input and increasing output of calories have a terrible record in long-term weight loss. As we recently saw, most of the contestants on the TV show The Biggest Loser regained all of their weight, and in some cases even more.

CICO also doesn’t take into account the body’s dynamics. The typical physiological response to a reduction in calories is a lowering of basal metabolism, that is, energy expenditure. Totally makes sense: the body senses a food shortage, so it compensates to conserve energy and, ultimately, life.

Enter Jason Fung, M.D., with his book, The Obesity Code.

Dr. Fung’s rich, informative book does a thorough job in demolishing CICO and other commonly held ideas in the field of obesity research. He meticulously describes how we’ve gotten so much wrong, what the real answers are, and how to implement genuine solutions for weight loss and the obesity epidemic.

How obesity became epidemic

Dr. Fung ascribes the beginning and continuation of the obesity epidemic to the promulgation of the U.S. Dietary Guidelines in 1977. The idea behind them was to lower cholesterol levels to combat heart disease by decreasing the amount of dietary fat. Carbohydrates were thought benign, so their consumption was encouraged. But not only did the experts get cholesterol wrong as a cause of heart disease, they didn’t understand the consequences of increased carbohydrates, and especially sugar, in the diet.

But Fung points out that it’s been known for literally a couple of hundred years at least that carbohydrates are fattening, and that even until a few decades ago, it was common knowledge, even among doctors, that cutting carbohydrates was the most effective way to lose weight.

The heritability of obesity and the thrift gene hypothesis

Fung shows that obesity is highly heritable, with up to 70% of variation in obesity explained by genes. Yet, as he also points out, and as I’ve argued with many people who ought to know better, the obesity epidemic arose within a single generation, so genes can’t account for it. No, it’s something in our environment.

The thrifty gene hypothesis, the notion that humans have a tendency to gain fat as a protection against famine, doesn’t wash either. Being fat also has disadvantages, for example in the speed from which you can escape a predator – in the case of humans, that other predator is most likely another human. If he can outrun you or overpower you, you’re finished. Animals don’t gain fat in the wild except when nature tells them, most obviously in preparation for hibernation.

The truth is that fat accumulation, like all other tissues and processes in the body, is highly regulated.

Hormonal regulation of fat

CICO theory runs into problems because the body responds to inputs and outputs. And the responses don’t necessarily go in the predicted direction. Not only does basal metabolism drop in response to fewer calories, but all calories are not the same. Hormonal and physiological responses differ greatly depending on whether the calorie in question is fat, protein, or carbohydrate.

If fat is regulated by hormones, which it is, could the differing hormonal responses to types of food contribute to obesity? Yes, they could. The most important hormonal response, Fung points out, is the insulin response. (More on that below.)


Why can’t we just exercise more, and and with the same number of calories taken in, lose excess fat that way?

This idea has at least three problems that render it ineffective. One, exercise makes us hungry. The body sensibly responds to an increase in energy expenditure by increasing out appetite so that we make up for calories burned.

Second, we respond to increased exercise by decreasing energy expenditure elsewhere, in non-exercise activities.

Third, most people greatly overestimate how many calories are used up in exercise. Basal metabolism and non-exercise physical activity make up a far greater fraction of most people’s energy expenditure.

“I can make you fat”: The Set Point

Fung discusses the paradox of eating too much. Overfeeding experiments in humans have shown that many people have great difficulty gaining weight, and that when they do, they lose it right away upon cessation of overfeeding.

Similarly, in starvation experiments, people lose weight, but focus their entire mental and physical being on food. They think about it, dream about it, and their metabolic rates drop dramatically. Upon cessation of the starvation experiment, they rapidly gain all the weight back, and often even more. You can see this in The Biggest Loser contestants.

So it appears that the body has a weight or body fat set point. If body weight is below the set point, physiological mechanisms kick in to cause weight gain. These mechanisms include lower metabolism and greater appetite.

If body weight is above the set point, metabolic rate increases and hunger decreases, causing weight loss.

So the obesity epidemic can be explained by the idea that most people’s body fat set points increased.

How did that happen?

Fung explains that the hormone insulin is the main player in setting the body’s fat set point. He says, “I can make you fat” by giving you insulin. He shows that either insulin itself given exogenously, or conditions or medications that increase insulin production internally, cause weight gain. Likewise, lowering insulin produces weight loss.


We’ve heard about the carbohydrate hypothesis of obesity. Carbohydrates raise insulin levels the most of any macronutrient, and thus cause weight gain. There’s much to be said for this.

And yet, as Fung points out, certain populations, for example in Asia, have eaten large amounts of refined carbohydrates and were not fat. In Japan and China, white rice made up a large fraction of food, yet until recently have not had an obesity problem. Similarly, the famous Kitavans eat about 70% of calories as carbohydrate — mostly sweet potatoes — and obesity is unknown there.

Insulin resistance

The key to obesity is not insulin, as the carbohydrate theory has it, but insulin resistance, the failure to respond adequately to insulin. As a result, the body’s levels of insulin increase, stay high, and never go down.

We normally avoid insulin resistance, as we avoid resistance to every other hormone, because these hormones are emitted in pulses, and the body never develops resistance to them. The hormones increase, have an effect, then decrease before resistance develops. growth hormone, for example, is largely released during sleep, then it decreases.

Normally, in response to a mixed meal, insulin rises, then when it’s done its job, falls. The body does not develop resistance.

When insulin rises and doesn’t fall, resistance develops in a vicious circle: more insulin, more resistance, then more insulin secreted to try to overcome resistance, etc.

Low insulin levels are required for fat loss. When insulin levels stay high, the release of fats from adipose tissue is greatly inhibited.

So how does insulin resistance come into being in the first place?

One of the main culprits in insulin resistance is constant eating. In this part of the book, I was happy to see that Dr. Fung echoes what I wrote in my book Stop the Clock: When you eat is as important as what you eat.

Think back to the 1960s, before the obesity epidemic began. (Easy for me, I was a kid then.) Did people eat health foods, tons of fruits and vegetables, watch the fat intake, avoid sugar? Hell, no. They (we) ate lots of crappy food. Oreos, soft drinks, pizza, and my favorite, Hostess Cupcakes. Though we didn’t eat these all the time. Most meals were eaten at the table, and little was eaten elsewhere, in contrast to now. And was 70% of the population overweight or obese? No.

Back in the 60s, we didn’t eat all the time. The twelve or so hours between dinner and breakfast provided a natural period of abstention from food, of fasting, that helped prevent insulin resistance.

It follows that “grazing”, the highly promoted practice of eating often, has been one of the most destructive of allegedly beneficial health practices devised in modern times. Snacking is great for promoting insulin resistance too.


Dr. Fung ends his book by showing what is needed for truly sustainable weight loss. Among his steps are a reduction in sugar and refined carbohydrates, moderate protein intake, and increased consumption of natural fats and of fiber.

But perhaps more importantly, and something that sets this book apart from others in its genre, is Fung’s advocacy of intermittent fasting. The practice of fasting can help reset the body weight set point by decreasing insulin resistance.

The practice of fasting has generally been denigrated in the mainstream. I hear people refer to it as “starvation”. Among the experts, you often hear that “breakfast is the most important meal of the day” – an assertion that Dr. Fung shows to be utterly false.

Why is fasting so denigrated, or at the very least, unappreciated?

Here again, I’m happy to see that Dr. Fung reaches the same conclusion that I have here and in many other health interventions: no one makes any money by telling you to eat less often.

The Obesity Code is an instant classic in this field, and is fully worthy of being placed in the same category as Gary Taubes’ Good Calories, Bad Calories and Nina Teicholz’s The Big Fat Surprise. While I’ve touched on some of Dr. Fung’s main points in this review, there’s far more in the book, and I highly recommend it to anyone interested in the topic of obesity, whether from a theoretical or practical point of view. I learned a great deal from it, and it’s fascinating and well-written, a genuine page turner.

PS: I discussed intermittent fasting in two of my books, Stop the Clock: The Optimal Anti-Aging Strategy, and Top Ten Reasons We’re Fat – both available at Amazon.

PPS: Check out my Supplements Buying Guide for Men.

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  1. Jay says:

    Also came across this, somewhat relevant and new research: almost 50% of Alzheimers is due to hyperinsulinemia – same enzymes are used to degrade insulin and beta-amyloid plaque, so when insulin is high, b-a plaque is not broken down properly as enzymes are too busy with insulin. https://m.stern.nyu.edu/faculty-research/b-school-innovation-professor-discovers-pathway-between-diabetes-and-alzheimer-s-disease

  2. Jay Campbell says:

    Great commentary Brother. It’s all about Insulin Sensitivity. Always has been. The neuro-protective effects of Fasting, suppression of insulin signaling and natural increase of glucagon/GH are what make it the #1 option for maximum fat loss and muscle preservation.

    • P. D. Mangan says:

      Thanks, Jay. Hopefully, intermittent fasting will increase its, well, market share – and it will thanks to advocacy from men like you who are in fantastic shape.

  3. Jay Campbell says:

    Yes. It’s why it’s known as Type III Diabetes. Lots of fascinating research already exists in the Medical community about this.

  4. Charles Grashow says:

    “The Obesity Code is an instant classic in this field, and is fully worthy of being placed in the same category as Gary Taubes’ Good Calories, Bad Calories and Nina Teicholz’s The Big Fat Surprise. ”

    Then it’s crap like the other two.

    • Tuba says:

      What I like about comments such as yours, Charles, is that it is a self-correcting stupidity via an early death.

    • Anon says:

      Congratulations, Dennis. I believe this may be your first troll. You can’t say you’ve made it to the “Big Time” until you’re on the radar of trolls and paid agitprop organs (AKA perceived competitor’s marketing dept’s).

      • charles grashow says:


        1) Are all of these people trolls as well?
        2) If soimeone disagrees does that automatically make them trolls?

        Good Calories, Bad Calories: The Mythology of Obesity, or The Mythology of Gary Taubes?

        Thin Body of Evidence: Why I Have Doubts about Gary Taubes’s Why We Get Fat

        The Carbohydrate Hypothesis of Obesity: a Critical Examination

        Good Calories, Bad Calories by Gary Taubes ~ Reference Check Posts

        • P. D. Mangan says:

          I read your first link, and I think there’s some right and some wrong in it. For instance, his first point, that obese people eat a lot more than lean, is generally correct, and that few researchers deny this. (Although The Biggest Loser contestants who regained weight have lower metabolic rates, so it wouldn’t be necessary to eat more than lean people in that case.) Maybe Taubes denies it, I don’t know. But Krieger writes, “Researchers insist that overeating causes obesity because that’s exactly what the data shows, despite Taubes’s attempts to spin it otherwise.”

          No, it doesn’t. There’s an association, and doesn’t prove causation. Most low-carb writers that I’m aware of claim that a metabolic defect causes the (soon-to-be) obese to eat more. So excess calories is a middle step, necessary but not sufficient for weight gain.

          I agree with Krieger that there’s no contradiction between poverty and obesity.

          As for the Pima, it seems clear enough that it’s *refined* carbohydrates and sugar that causes their obesity. The slender Mexican Pima are not eating that stuff, as far as I know.

        • Anon says:

          “If soimeone (sic) disagrees does that automatically make them trolls?”

          No, of course not. It takes an incendiary statement without context or any supporting argument to be a troll. Also, twisting the words of others: troll. And spamming comments with a bunch of ancient links, again without any context or discussion: classic troll. It’s hard to believe anyone can be so self-unaware.

        • Richard says:

          Causation, like the words fault and truth, is an extremely difficult problem in language and in practical terms. Causation suggests that we (or someone) “knows” how the system works. What Fung and the others, (Taubes for example) have effectively shown is how the the results come out, not necessarily the chemistry involved.

          And what has been shown is that when you eat is probably (really, as I see it, almost certainly) more important than what you eat or how much you eat, in terms of insulin and, thus, obesity. Thus the CICO model is not particularly helpful. What is helpful and explanatory is the insulin pulse concept and the basis for saying that insulin resistance is a result of too much continual production of insulin. And in the end the continual production of insulin leads to obesity.

          And for me, this is sort of how science progresses, with different people advancing to level of understanding. Suppose Taubes did not have the entire picture completely in view? Does that mean he is a fool, or worse? Is it more significant that people are cautious about affirming a new approach to the problem? Particularly when, with the “Whole Health Source” blog, this insulin theory is contrary to the view of that writer?

          And so yes, your initial post comes across as hostile and too troll like. This is a difficult issue and has so far stumped a large number of intelligent people. Worse still, there are people who seem to have reasons to avoid or dismiss or denigrate this no-cost method of solving the problem. As Dr. Fung points out in his blog, and in his book I am sure, fasting is a no-cost solution, and actually saves you money. How good is that?

        • 123watchdog says:

          No, but for an opposing view to be taken seriously, try something with more substance and respect than “Then it’s crap like the other two.”

      • Tuba says:

        Agreed. That said, the studied ignorance of the Old Guard will not go away until those who make a living off slinging dusty garbage die or retire.

  5. Jerry says:

    Right on PD! The book is a must have.

  6. FormerlyBigFatGuy says:

    Hostess Cupcakes? That brings back memories.

    My mom shopped at a store that sold stale Hostess Cupcakes for two cents apiece. She loaded up the shopping cart with those things. I ate them for breakfast, took them to school for lunch, ate them again when I got home. I practically lived on Hostess Cupcakes. I was not fat in those days. Too young, I suppose.

    Going away to college broke the Hostess Cupcake pipeline, and I did not eat any more for several years. I bought a Hostess Cupcake at 7-Eleven one time on a whim. It did not taste anything like I remembered. It was soft and creamy. I realized that I had never actually eaten a fresh Hostess Cupcake.

    That was a long time ago. Poor old mom did not know any better. No carbs/sugar for me these days. That stuff is poison.

    • P. D. Mangan says:

      Hi Formerly, yup, Mom didn’t know any better – mine either. Which reinforces my point about obesity a few decades ago: not much of it, yet the food was not so great. I rarely touch any of that stuff these days – certainly not Hostess Cupcakes, which I believe are not made anymore.

      In the book, Fung mentions that of course you should celebrate with tasty food on your birthday or at a wedding, just don’t make it a habit. Most people however, want to eat this way much more often than at celebrations.

  7. Richard says:

    Thanks for your review of this book. I have been doing the 20-24 hour IF routine for a month or two now, with good results. I’m 71, a former college gymnast, and I have lost about 15 lbs of fat. I’m at 155 now, and I can still bench press 180, just like before I started, or maybe a little better, so no muscle loss while doing this. Which is consistent with Dr. Fung’s assertions regarding production of growth hormones and testosterone.

  8. AJ says:

    I have read Dr Fung’s book as well as Good Calories Bad Calories. Incidentally, have also purchased stop the clock, so I am doubtlessly in the low carb high fat / IF crowd.

    The only thing I would like to point out, is that if the science is correct (the way I interpret it), then one would have to be in a ketogenic (fat burning state) already for IF to work. More specifically, if you’re burning sugar, then 18-24 hour of fasting will simply deplete your glycogen, which you will rebuild back up once you eat your meal.

    The only way I can see IF working is if you’re already in a ketogenic state (ie burning fat for fuel by default instead of carbs), and fasting then allows you to focus on your body fat as a source of energy, rather than stored glycogen.

    This is something that is not made clear in his book, or his blog. Perhaps it’s implied.

    • P. D. Mangan says:

      The mistake (as I see it) in your reasoning is that even with glycogen reserves, the body doesn’t burn pure carbohydrate. It’s always burning a mix of carbohydrate and fat. The more that insulin declines as fasting occurs, the more fat that’s burned. It isn’t necessary to have completely depleted glycogen to burn fat. Even exercising, even weightlifting, you burn a lot of fat, and only in the most intense exercise does carb burning really ramp up. When glycogen *is* fully depleted, then ketosis can begin, along with gluconeogenesis.

      • AJ says:

        That’s interesting I did not know that. I always thought it was a linear step by step process.

        It would make sense, given on how some folks can lose fat without being strictly ketogenic.

        Thanks for clearing that up.

        Excellent site, tons of information. The Red Pill of weight loss, so to speak.

      • Rick Duker says:

        That’s a very important point. Dr. Fung also shows that some proteins can provoke a larger insulin response than some carbs without raising blood sugar. This insulin response from protein should not be underestimated as a contributor to insulin resistance which means that low carb high protein diets are self defeating.

  9. Pissedman says:

    I applaud your website and information. I would put you in the top 10% of sites I visit on the cutting edge of aging reversal. I think in this Area of mass population issue we have to. Consider the we have been exposed to a great deal of herbicide (roundup) in our food and water. We have also been exposed to GMO’s and treated like a bunch of Guinea pigs. So I believe that the results of 3rd party testing that show huge liver and kidney toxicity that could affect or metabolism. Also, there are some interesting findings in metabolism and gut bacteria. Naturally, gut bacteria are highly affected by roundup and GMO’S so maybe by a different route our metabolism disruption I’d occurring.

    • P. D. Mangan says:

      Thanks, P-Man, I endeavor to please, hopefully I’ll be expanding to bigger horizons.

      BTW, every indication is that metformin and berberine work at least in part by changing gut flora, so that speaks to your comment.

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