Should the Calorie Die?

What two recent books contribute to the "Calories In, Calories Out" debate

In my Books I Read in 2023 post, I promised a more detailed review of two books about metabolism and calories: Burn and Why Calories Don’t Count. Both books provided good overviews of how the calorie came to dominate nutrition, as well as primers on human metabolism. I’ll summarize the main message of the two books, cover their similarities and differences, and then consider where the Calories In, Calories Out (CICO) debate stands in light of these books’ claims.

A brief summary of the two books

Burn

Burn was written by evolutionary anthropologist Herman Pontzer and hence takes an evolutionary perspective of metabolism by comparing humans to apes.¹ Pontzer has shown in his academic work that energy expenditure measurements of Hadza tribespeople seem to be close to typical Westerners despite the Hadza people being much more physically active.² This leads Pontzer to conclude that daily energy expenditure is a variable controlled by the body: energy expenditure doesn’t dictate weight change, but rather responds to weight change. This is a radical idea from the standpoint of basic CICO accounting. It implies that there are much more complex metabolic processes involved in determining a person’s weight. Another interesting insight from Pontzer is that the human body appears to have an upper limit on the amount of calories it can absorb in a day.³

Why Calories Don’t Count

Why Calories Don’t Count was written by biochemist and neuroscientist Giles Yeo and therefore focuses more on metabolism at the cellular level. It details how the body absorbs different macronutrients and emphasizes that all calories are not created equal. There are at least five mind-blowing ideas I learned from this book:

1. Macronutrient information on nearly all food labels is riddled with substantial amounts of measurement error.

2. At the same time, different macronutrients have different levels of “caloric availability.” Thus, the calorie numbers on food labels should be thought of as “potential calories” while the calories your body actually absorbs should be thought of as “effective calories.” Fat and carbs are much more readily absorbed by the body and hence have greater effective calories than protein or fiber. Metabolizing protein requires energy, which lowers the effective calories of protein.
   Combined, points 1 and 2 imply two different ways in which nutrition information may be wrong.

3. The body has complex mechanisms for deciding whether to burn or store metabolized energy. I believe this to be the crucial step in understanding the obesity epidemic.

4. “Processed” foods have more effective calories than “whole” foods, even with identical potential calories. This is mainly because whole foods contain more fiber. The book cites a randomized experiment where researchers had subjects eat a “whole food” grilled cheese sandwich or a “processed food” grilled cheese sandwich. The sandwiches each contained exactly the same number of calories (as measured by the food labels). The main finding was that the processed food grilled cheese took half the number of calories to consume in the body compared to the whole food sandwich. This difference in energy expenditure seems to be part of the story of why processed foods cause weight gain.

5. Everyone has a “fat carrying capacity” that is specific to themselves, but which also manifests in racial differences (e.g. Polynesians have much larger fat carrying capacities than Asians). Therefore, the range of “healthy” BMIs is different across people. This means that not everyone who looks overweight is in a risky health situation; neither is everyone who looks thin in a favorable health situation.

Similarities in the two books

Both books emphasize that a calorie deficit is key to weight loss, and that “all diets work because they induce caloric deficit.” Another common theme was that “you can’t outrun a bad diet” and that diet and exercise need to be combined to achieve lasting weight loss and improved health. Finally, both books emphasized the importance of sleep, mental health, and stress in maintaining a healthy weight.

A major idea that I thought both books missed was the role of fasting in regulating metabolic processes.⁴ Fasting is a straightforward way to achieve a caloric deficit, and it seems to remedy multiple metabolic issues at the same time.

Where does this leave the “Calories In, Calories Out” (CICO) debate?

Here is a brief summary of the current state of CICO debate:

Pro-CICO (“you can only lose weight by sustaining a calorie deficit”)

• Both books ultimately endorse CICO by concluding that a caloric deficit is required for weight loss.

• The bodybuilder types on YouTube also agree with this approach.

Anti-CICO (“calories are not a good first-order approximation of food’s metabolic impact on the body”)

• Slime Mold Time Mold explain that CICO must not be true (or, at least, is not to be taken literally) because it implies a linear relationship between weight change and caloric deficit/surplus.

• Miles Kimball argues that the body’s insulin response to ingested food is a much more important first-order concern than the calorie content.

• Ryan Andrews argues that the brain is programmed to feel satiety with 3–4 pounds of food and meeting this weight requirement with whole foods is the best way to not overconsume while still feeling full.

While the two books seem to advocate for CICO, they also both admit that calories are not a good sufficient statistic for nutrition and instead that health should be managed in a multifaceted way. The results in Burn specifically show that there are key nonlinearities in how the body regulates energy expenditure. Burn also quotes the book The Hungry Brain which emphasizes that body weight regulation is hormone-driven and originates in the hypothalamus part of the brain. Beyond emphasizing measurement error in caloric intake data, Why Calories Don’t Count also discusses the concept of intermediary metabolism, which is a set of metabolic processes that determines whether energy should be used now or stored for later.

After reading the two books, I’m still confused about how weight loss works. If it’s simply about keeping a caloric deficit, then calorie counting should encourage weight loss! At the same time, if energy expenditure is as tightly regulated as Pontzer findings seem to imply, then it seems like overweight or obese people have no hope of losing weight. Yeo seems to embrace this in Why Calories Don’t Count as well as on his social media accounts by frequently appending the hashtag “obesity is not a choice.”

Burning Questions (no pun intended)

So what do the ideas and perspectives in these two books contribute to the following mysteries of weight gain?

Why do obese people continue to remain obese?

This is obviously one of the world’s Trillion Dollar Questions. Pontzer seems to argue that obesity is driven by poor diet and poor regulation of energy expenditure, especially by the brain (and this latter point is borrowed from Stephan Guyenet). Yeo claims that body weight is highly heritable and is even more so in “less privileged” environments (40% heritable in most-privileged, 80% heritable in least-privileged). He goes on to basically say that obesity is unsolvable (or, that it won’t be solvable until we solve poverty and deprivation).

I find these explanations unsatisfying. To me, it stands to reason that, regardless of what the bathroom scale says, most (if not all) people will be better off if they don’t eat so many highly processed foods and if they focus on other aspects of their health (sleep, stress, exercise, mindfulness/mental wellness, social relationships, etc.).

To put it a little more bluntly: I expect that if we moved people out of Western culture and had them live with the Hadza for some number of months, they would rapidly lose weight and start to look like the Hadza (up to genetic differences). Likewise, if we took some Hadza and moved them into the West and fed them like Westerners, they would start to develop metabolic deficiencies quite rapidly.

Because there still seems to be no clear story about what causes weight gain, a man by the name of Lucent posted all of his diet, nutrition, physical activity, and health data online and created a contest to see if someone can come up with a validated model that explains his weight fluctuations. The basic premise of the contest is, if Lucent lived in ancestral times, he wouldn’t be as heavy as he is right now, so what can he do to offset the negative impact of his current environment?

If the body’s metabolism is so tightly regulated, why can’t it just burn off any excess calories I consume?

A seemingly simple solution to obesity would be to program the body to make use of its excess energy stores, which would reduce fat levels. Unfortunately, it’s not so simple.

My understanding, gleaned from these two books and other research, is that the body prioritizes storing any excess energy it ingests. This is due to evolutionary adaptation to help our ancestors survive famines. Moreover, fat is the preferred long-term storage method because it is so energy dense.

Another evolutionary adaptation, known as “adaptive thermogenesis,” is to slow down metabolism when excess calories are consumed. This is tied to the previous point about prioritizing energy storage. Adaptive thermogenesis is driven by the hormone leptin.

My understanding is that the body’s decision to “burn” or “store” energy also depends on what food is being ingested and what baseline hormone levels are at the time of ingestion.

All of this is to say, people who are obese are actually less likely to use their excess fat stores for energy. In short, there is a vicious cycle that leads to obesity in the first place: hormone levels are off, leading to excess fat storage, which causes adaptive thermogenesis, which further disrupts hormone levels, leading to even more fat storage, …

What sort of hacks are available to me to help me lose weight?

The science at the moment seems to indicate that, while most people have foods or behaviors that are specific to their own health, the following broad-based advice seems to work (or at the very least, do no harm):

• Eat more fiber and protein. This will help you feel more full and help you avoid overeating, according to Yeo.

• The self-proclaimed “Glucose Goddess” Jessie Inchauspé claims that flattening glucose curves—meaning, reducing the glucose response to meals—has myriad health benefits. I will plan to write a separate post in the future more critically evaluating these claims.

• Two Meals a Day advocates for increasing the amount of time you walk as this can help a person become “fat adapted” or “metabolically flexible” (meaning their body chooses to utilize its fat stores for energy). The book also emphasizes eating more “ancestral” foods such as organ meats or fermented foods.

• Building muscle mass seems to reduce fat.

Conclusion and Unresolved Questions

While these two books added to my knowledge of metabolism and calories, there are still several looming questions that are left unanswered.

• Given that both caloric intake and expenditure are measured so poorly, how can a person be certain they are actually in caloric deficit or surplus?

• Is it possible to lose weight while simultaneously consuming more calories than expending, by targeting some part of the hormone cycle?

• Is blood sugar as important as the “Glucose Goddess” makes it out to be?

• How exactly does the basal metabolic rate adapt?

• How important is the gut microbiome to maintaining weight?

• What is the precise role of hormonal interplay among “stress” and “hunger” and “satiety” hormones?

• Why does walking seem to be such a magic bullet for weight loss?

• What exactly is it in mass produced food that seems to be so bad for people?

• Why does the potato diet work?

Other links

• See here for a Vox writeup of Pontzer’s work.

1. Humans have evolved to have higher metabolic rates (i.e. number of calories required to maintain baseline bodily function) than other primates, by 20%-50% depending on the species. This is because the human brain is larger and more powerful, and because humans tend to live much longer than other primates (by 1.5x–2x).

2. These studies use “doubly labeled water” to get precise measurements of metabolism.

3. Specifically, (2.5 x BMR) calories, which is about 4,000-5,000 kcal for most people. Interestingly, Pontzer specifically mentioned Olympic swimmer Michael Phelps as a “mutant” in this regard and suggested that his ability to absorb more calories contributed to his athletic greatness because he could train harder and develop more muscles than his competitors.

4. In a Reddit “ask me anything,” Pontzer said, “There’s no magic to fasting beyond the reduction in calorie intake – [though calorie] reduction and weight loss often lead to improved health. For some, fasting and intermittent fasting work well as a way to curb calories. Some potential cons though, including getting hangry and potentially reducing your metabolic rate as your body responds to perceived starvation. Use at your own risk! (and again, no magic – just calories).”