I have heard many times that someone's "slow metabolism" is responsible for their obesity. Many times I've also heard that it isn't to blame.

Here's an example of a source claiming that slow metabolism isn't to blame:

Is it possible to be overweight because of a slow metabolism?

Answer from Donald Hensrud, M.D.

Probably not. There is such a thing as a slow metabolism. But slow metabolism is rare, and it's usually not what's behind being overweight or obese — that's usually a matter of diet and exercise.

Source: Mayo Clinic


Excluding rare and serious metabolic conditions, which should be diagnosed by a doctor, people's metabolisms tend to be within 200-300 calories of each other. This examine.com meta-analysis explains this in greater detail.

They conclude that:

Metabolic rate does vary, and technically there could be large variance. However, statistically speaking it is unlikely the variance would apply to you. The majority of the population exists in a range of 200-300kcal from each other and do not possess hugely different metabolic rates.

This review of 67 scientific studies found that:

"when adjusted for differences in fat-free mass, resting energy expenditure values in obese and nonobese individuals tend to be comparable"

and there is

"no association of baseline resting energy expenditure with weight change among 775 men during a 10-year period".

The review draws the conclusion that:

"Regarding metabolic factors, available data indicate that although there are variations in resting energy expenditure and in the thermic effect of food, there is little evidence that these variations contribute significantly to the observed trends in weight gain."

  • Doesn't a 300 / day calorie difference result in a 30lb / year difference in weight gain? I don't see how that's insignificant. – Turch Mar 23 '17 at 14:28
  • 'People' as described would account from a 5ft teen girl through to a 6ft man. Can you explain how 300kcal/day = 30lb? – John Mar 23 '17 at 16:24
  • 300 * 365 / 3500 (the commonly stated number of calories in a pound of fat). – Turch Mar 23 '17 at 18:42


It can be argued from an evolutionary standpoint that there shouldn't be much difference in metabolism rate among humans. (Except rare diseases). Because over an evolutionary scale, humans nearly all the time have evolved in conditions where food was scarce. We have wide availability of food only since very recent times and even now only in developed countries. Thus there must have been a high selective pressure on optimizing metabolism rate. Any abnormal metabolism rate (be it too slow or too fast) would have been washed out of the gene pool quickly. Thus we can assume that metabolism rate is very similar among all humans. Thus such things as a "slow metabolism" should not exist.

Source: Der Mensch als wärmetechnisches System (sorry, German; Translated title "The human body as a thermotechnical system"), University of Magdeburg, in section "Einfluß des Stoffwechsels" (influence of the metabolism).

Edit: The sources given by JJosaur already support the claim that people's metabolism lies within narrow ranges of each other.

So i'm only providing another source to support the specific view that metabolism has been optimized to the current value over evolutionary time scales here: Metabolic thrift and the genetic basis of human obesity

  • As there are plenty of sources arguing the opposite of your answer, a better source would really be good. Ideally, a peer-reviewed study that is specifically about slow metabolisms and obesity, or at least a text by a medical professional or a professor researching evolution, instead of a professor of thermodynamics speculating about evolution. – tim Mar 21 '17 at 11:18
  • 2
    Your evolutionary argument needs reputable sources. The way it is at the time of this comment, it is a poor fit for the site. Original research / napkin logic. – Mindwin Mar 21 '17 at 14:31

The usual factors include:

  1. Calorie intake
  2. Energy expenses (your day to day activities)
  3. Health condition (e.g. thyroid issues)

As one ages, 2 will go down and the individual will put on weight if 1 remains the same level...

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