Individual differences of metabolism is like the health-equivalent of IQ–something that is often downplayed, minimized, or denied–but of great importance (unlike IQ, at least it’s not taboo–yet). It is trendy to say that metabolism does not matter in so far as weight loss is concerned, or that fast or slow metabolisms are myth, or such differences of individual metabolism are only very tiny, as seen on Reddit:
But to say that slow or fast metabolism is a myth is like saying that the existence of intelligent or unintelligent people is a myth, or that tall or short people are a myth. Yes, the kid who is eating glue is just as smart as the kid who is learning algebra. No difference at all. We’re supposed to somehow accept this with a strait face.
There is as much or even more individual variance for metabolism as there is for IQ relative to the mean (the coefficient of variation). As shown below, controlling for weight and height, there is considerable individual variance of individual TDEE (total daily energy expenditure):
And:
[0]
According to a study of total daily energy expenditure (TDEE) of subjects who had lost weight (WLM), the mean TDEE is 2495 kcal/day with a standard deviation of ±366.
PAEE in WLM (812±268 kcal/d, mean±SD) was significantly higher compared to both NC (621±285 kcal/d, p<0.01) and OC (637±271 kcal/d, p=0.02). As a result, TDEE in WLM (2495±366 kcal/d) was higher compared to NC (2195±522 kcal/d, p=0.01) but not significantly different from OC (2573±391 kcal/d).
So diving the mean by the variance, we get a coefficient of variation of 6.82 (after taking the reciprocal). This is remarkably close to the same coefficient of variation for IQ, which is 6.67 (a mean of 100 divided by a standard deviation of 15).
Similar to IQ, a good chunk of individual variance of BMR (basal metabolic rate) cannot explained by anything that is apparent or measurable (like body composition) or environmental:
The basic metabolic rate varies between individuals. One study of 150 adults representative of the population in Scotland reported basal metabolic rates from as low as 1,027 kilocalories (4,300 kJ) per day to as high as 2,499 kilocalories (10,460 kJ); with a mean BMR of 1,500 kilocalories (6,300 kJ) per day. Statistically, the researchers calculated that 62% of this variation was explained by differences in fat free mass. Other factors explaining the variation included fat mass (7%), age (2%), and experimental error including within-subject difference (2%). The rest of the variation (27%) was unexplained. This remaining difference was not explained by sex nor by differing tissue size of highly energetic organs such as the brain.[26]
In terms of socioeconomic outcomes, the difference between an IQ of 100 and 115 is huge, such as college completion, lifetime wages, wealth and so on. The difference between an IQ of 85 and 100 is the difference between completing high school (before standards were lowered) versus dropping out. This is pretty significant. Yet somehow when it comes to metabolism we’re told to believe that a 1-2 sigma difference between individuals is meaningless, or does not exist (when clearly we can see it does). That makes no sense.
I think the misunderstanding is that if two individuals weigh the same despite having differing metabolisms, then in that sense metabolism does not matter, as both individuals are at hemostasis. But it matters if the objective is weight loss, like in the context of treating obesity, or for bodybuilding, in which leanness and aesthetics is the desired result.
To discount metabolism because two people weigh the same is like arguing that because someone with an IQ of 100 can do arithmetic that there is no difference between him and and someone with an IQ of 130, who can also do arithmetic. But this is a very low bar. If you bump up the difficulty to something like calculus, then it’s reasonable to assume that the additional 30 points helps greatly. Likewise, having a faster metabolism helps with the physical stressor of weight loss.
Dr. Stephan Guyenet blames obesity on hyperpalatable foods which trick our minds. Others blame seed oils. But individual differences of metabolism–specifically, the existence of metabolic outliers–can explain how a small minority of individuals can successfully lose weight with diet and exercise alone even if the majority of dieters fail.
Genes do a much better job of explaining how two individuals in otherwise similar environments differ so much in body composition and weight, but in reconciling genes, which are slow, with the seemingly rapidly rise of obesity over the past century, we run up against the limitations of science. However, the rise of hyperpalatable foods can explain rising rates of obesity among individuals on the left-side of the metabolic distribution. It stands to reason people with worse genes are more vulnerable to these foods.
For either weight loss in the context of treating obesity or for aesthetics like bodybuilding or modeling, I posit metabolism determines how much weight loss or leanness can safely and practically be achieved. Although this is not to discount environment, like dieting, at some point everyone hits their genetic limit. Although new GLP-1 drugs like Wegovy or Ozempic can help, even still, metabolism is still a key determining factor for how much weight someone will ultimately lose safely and practically, even when on such drugs.
In upcoming posts I will give hypothetical examples, and then move to the literature and real examples. But as shown above, we see that slow metabolisms cannot be a myth, as there is enormous variance between individuals, similar to IQ.
[0] Thomas, Diana & Watts, Krista & Friedman, Sara & Schoeller, Dale. (2019). Modelling the metabolism: allometric relationships between total daily energy expenditure, body mass, and height. European Journal of Clinical Nutrition. 73. 10.1038/s41430-018-0230-y.