Individual differences of metabolism are real and matter

I saw a this post going viral on Reddit, “Why do I gain 5 lbs just looking at bread but my friend eats like a raccoon in a Taco Bell dumpster and stays fit?” The fact many many people have observed this and can thus relate, explains how the post went so viral. We all know those people or have seen them in action.

Assuming the poster is tracking exactly how many calories his or her friend is consuming (some people may eat a lot at once when other people are around, like social situations, and little food otherwise, whereas others graze alone), as well as accounting for physical activity, it’s likely genetics.

It’s funny how so many people in the comments downplay the role of genetics. To these people, everyone is cut from the same die/mold when it comes to metabolism. People vary so much by height, strength, and other attributes which are innate, so why is metabolism the exception?

Even people, on Twitter, who subscribe to a strongly hereditarian/HBD-centric view of the world, like about IQ, find it hard to accept, or downplay the importance of metabolism in so far as obesity is concerned:

Metabolism in the process in which an organism converts nutrients into energy at the cellular level. How can this not play a major role in obesity, which is a marked disequilibrium of this process. In the above tweet Razib Khan responds in agreement with Philippe Lemoine, who writes, “When people say that the propensity for obesity is largely genetic, they tend to think about differences in metabolism, but my guess is that it has at least as much to do with self-control.” But consider that having a faster metabolism (or more specifically, a less efficient metabolism) means being able to eat more food without becoming obese, hence less willpower is required.

Others may concede that there is only a 300-calorie/day difference between people with ‘fast’ or ‘slow’ metabolisms, which is also false. The actual difference according to the research I have done is much more–possibly thousands. So imagine two homogenous, healthy 6-foot-tall males who are both moderately active, but one has a TDEE (total daily energy expenditure) of 3.5-4.5kcal/day, which is at the high end of the range, compared to 2-2.5k/day for the other, on the low end. This represents as much intra-individual variance as something obvious like IQ, so to deny that fast or slow metabolisms exist is as false as denying that intelligent or unintelligent people exist.

The obvious rebuttal is that IQ scores are normed to ensure a normal distribution exists. But the actual assessed differences in terms of cognitive performance or achievement of, say, 30 IQ points, which is two standard deviations, are significant. A 30 point difference can make the difference between earning a doctorate versus merely graduating from high school. Or ‘special ed’ versus ‘gifted’ classes. So, IQ scores are not just social constructs or arbitrary, but reflect definite individual differences of intelligence that have measurable real-world consequences.

Some people generate more NEAT (non-exercise activity thermogenesis), like fidgeting or other non-purposeful movement, or have a higher TDEE due to internal organs consuming more energy relative to body mass, and other processes that are not well understood but can account for the enormous variance of metabolism between otherwise identical individuals. Another rebuttal is that individuals on the high-end of TDEE would overheat. This too is false. Individual differences of core body temperature can only explain a small amount of this variance.

But can’t exercise overcome a low NEAT or raise it? Not really. Because exercise, by definition, is purposeful and voluntary. This is why daily step counts are far less potent compared fidgeting and other subconscious motor activity. When the body senses exercise, it becomes much more efficient, whereas this does not apply to NEAT. Or at least this is my theory, as it explains why so many people do ‘daily step counts’ or go to the gym, yet cannot lose weight. It’s also backed by the ‘constrained energy model’, popularized by Herman Pontzer, which posits (and is supported by empirical evidence) that the body adapts to exercise by burning fewer calories at rest later.

Same for set point theory. In overfeeding studies, there is considerable individual variance as to how many surplus/overfed calories are stored as fat or burned, and this is likely innate (due to NEAT, among other factors). Better genetics means more ‘waste heat energy’ or partitioning of nutrients for muscle growth or for the brain, instead of fat storage. Or more fidgeting. Some people really can eat more without getting fat. Life is unfair in that way, like it’s unfair in other ways too.

From the report, “The Effects of Overfeeding on Body Composition: The Role of Macronutrient Composition – A Narrative Review,” in regard to overfeeding:

The average body weight gain was 2.2 kg, of which 50% was FM. However, there was considerable variability in the response to overfeeding. It is notable that some individuals lost FM and reduced their body fat percentage despite eating an additional 1,000 kcal per day. Moreover, there was a significant genotype-overfeeding interaction for changes in body weight, FM, and FFM, suggesting that genetics do play a role in determining body composition changes in response to overfeeding.

and

During overfeeding, the additional 1,000 kcal was provided from sherbet, fruit juices, margarine, corn oil, and cookies, with 25% consumed at breakfast and the remainder split between the other eating occasions. The average gain in body weight was 2.5 kg, of which 68% was FM. However, some participants gained as little as 0.25 kg while others gained 2.8 kg.

That’s why it’s called HBD; the ‘D’ is for diversity. It’s clear people differ greatly in terms of how they process food.

Again, why people vary so much in terms of metabolism not that well understood. A certain percentage of people with late-state cancer, particularly of the lung, stomach, pancreas or esophagus, lose a lot weight (cachexia) of fat and muscle, and this cannot be explained by overheating or physical activity (it’s not like late-stage cancer patients are moving around much). And no amount of forced feeding can reverse the cachexia, so the calories are going somewhere.

So back to my earlier example, if both males are at stable weight regardless of metabolism, why does this difference matter? It matters in the context of an external or self-induced stressor, such as dieting. In this case, the individual with the faster metabolism is at an advantage due to burning more calories at rest, hence more fat loss. This can explain how some people are able to become lean or stay lean compared to others, among other variables, but I posit metabolism is a key one. From the post: “Metabolism , fitness influencers, and looking good into adulthood“:

At some point everyone hits a plateau, in which further weight loss is not possible at a given daily calorie level, controlling for weight and height. Where this stall vs. weight occurs is mediated by genes to a large extent. Someone with good metabolism genes will stall out a lower bodyfat percentage relative to calories consumed. Someone who stalls out at 2,000-1,600 cal/day while still being overweight has poor genetics for leanness, as cutting more calories will be too unpleasant or infeasible (many such cases), or lead to nutritional deficiencies and muscle loss due to eating so little. By contrast, someone who is able to keep losing weight at a higher intake, conversely has better genetics for being lean; so in this case, producing a lot of waste heat energy. Waste is good in this context, whereas wastefulness is otherwise seen as a negative in life.

Metabolism is one of those things that dot not necessarily favor the athlete or ‘fit’ people. Like IQ, there is a sort of unfairness to the whole thing, in how it does not agree with our notions of virtue. Someone can be out of shape and still have a great metabolism, whereas former athletes not uncommonly ‘blow up’ when their careers end, or after high school or college. Differences of athleticism are more obvious or important early in life, whereas metabolism matters more later in life. Those who can stay lean or thin throughout adulthood can reap the status and other social benefits that come with this.

Another myth is that a fast metabolism makes it harder to build muscle, and that people with slower metabolisms build muscle more readily. This is one of the dumbest myths out there, and very existence of obese people disproves it. If this were true, obese people would have much more muscle instead of storing so much fat. But any additional lean mass from obesity is due to the enlargement of the internal organs, like the liver especially and extra blood and water volume, not extra muscle. If anything, being sedentary from obesity may hinder muscle growth and lead to atrophy. It’s very much possible for someone who is lean and has a fast metabolism to build muscle at a sufficiently large surplus, whereas a fat person with a slow metabolism only gets even fatter at a surplus.

As for why muscle does not stave off weight gain, any extra muscle burns only a tiny amount of calories relative to the internal organs (specifically the brain and the liver) and other processes, like digestion and the immune system. An extra 30 pounds of muscle, which for a 170 lbs person is a significant amount of mass and is at the upper end of what is possible without steroids, is only 300 extra calories/day of TDEE, which is two cans of Cola. An obvious example is the tendency of Polynesians to be obese despite also possessing more muscle mass compared to Europeans or other groups. This unfairness of metabolism, combined with the inability to raise it, similar to IQ, can explain efforts to downplay or minimize it.

Individual differences of metabolism can also explain how some people lose more weight on GLP-1 drugs compared to those who lose less. People with faster metabolisms may be more successful at weight loss if already obese. So a 300-lbs person who eats 10,000 calories/day to be weight stable will find it easier to lose weight compared to to a 300-lbs person who is stable at 4,000 cal/day. The first guy will lose much more weight more rapidly owning to having a much bigger metabolic furnace compared to the second guy. Thus, counterintuitively, being a bigger glutton means more weight loss and easier weight loss. Unfortunately, there are no studies that investigate the link, if any, with metabolism and dieting success or GLP-1 drugs, although if I had to hazard a guess, it exists. It would seem obvious to test this, but studies are wanting.

So back to the main topic–the apparent ability of some fortunate individuals to overeat ‘bad’ food without gaining weight or getting fat–I believe there is some truth to this at a biological level. I think it’s better to just accept this fact, also like how some people are taller or smarter or more attractive, than to just invent narratives otherwise. Metabolism denialism just seems like a different version of IQ denialism. Given how obesity is a major worldwide problem, understanding metabolism is necessary in attempting to treat it. Denying its role doesn’t do anyone any favors, even if pretending otherwise may make us feel better about ourselves.