Are there any downsides to having a good metabolism?

[mr.jp]

@Chronos

Just what do you think a “fast metabolism” means? That’s like saying “I haven’t seen any evidence for gravity. I think there’s just a force that pulls massive objects together”.

I’m quite confident that many people, the OP possibly included, means something else by “fast (or “good”) metabolism”. Like it’s an innate thing, that is independent of how active you are.

[Chronos]

Or maybe it’s an innate thing, that functions by making you more active.

[mr.jp]

@Chronos

Or maybe it’s an innate thing, that functions by making you more active.

Yeah.

I can reformulate my statement thusly:
Insofar as people have different metabolism rates, I doubt that it is caused by something on a molecular level. Instead I think it is caused by differences in activity levels.

Since most people are close to weight stasis, faster metabolism will mean a higher throughput of food. This has good effects, in that the person will get more vitamins and minerals. And bad effects, in that the person will get more toxins and carcinogens. My guess is that the good effects outweigh the bad.

[DSeid]

Elements of metabolic rate (a good explanation is here):

Resting or Basal Metabolic Rate (RMR). Biggest factor for that is the “fat free mass” (FFM) of the body and some from the “fat mass” (FM) as well. Varies significantly between people based on factors other than those as well but per this article maybe not so much of the variation is from hormones:

The major factor determining basal metabolic rate (BMR) is fat-free mass (FFM) (1–3), with some studies finding an additional contribution of fat mass (FM) (4, 5), but others failing to find such an effect (6, 7). Even when these factors are known, however, substantial residual variation remains … Hyper- and hypothyroid conditions lead to changes in BMR, but the effects of individual variations in thyroid status within the euthyroid range of variation remain unclear. Some studies (5, 36) have shown significant links of BMR to circulating triiodothyronine (T3) concentrations, yet other studies have failed to find such effects (37, 38). In the present study, we aimed to define the roles of FFM, FM, age, and sex and to examine whether residual variation in BMR once these factors had been accounted for was linked to concentrations of circulating leptin and thyroid hormones [T3 and thyroxine (T4)]. … Consistent with previous studies (1–3, 42) the dominant factor influencing this variation between individuals was the extent to which the individuals varied in their FFM. … The mean BMR of all subjects was 6279 kJ/d. The minimum was 4301 kJ/d and the maximum was 10 455 kJ/d. The SD was 1199 kJ/d, and the CV was 19.1% … Our studies confirmed that, in this sample of adults, FM was an independent factor—although the contribution to the total variance that was explained by differences in FM was relatively small compared with that explained by FFM … Like many other studies, our work has indicated a large between-individual variation in BMR that cannot be explained by morphologic characteristics, including sex and age. We show here that 2 important physiologic candidates that might explain this variability, namely, variations in circulating concentrations of leptin and T3, do not account for this unexplained variation in a population of 150 white adults. In men, however, 25% of the residual variance was associated with variation in circulating concentrations of T4. No equivalent effect was found in women.

The Thermic Effect of Food (TEF). We expend energy digesting the stuff. That varies with what is eaten but I do not think much between people.

The Thermic Effect of Activity (TEA). That’s things like exercise and work; purposeful acvity. Yes, it varies a lot between people but I do not think that is what you are talking about.

Non-Exercise Activity Thermogenesis (NEAT). Fidgeting. Standing at the counter rather than sitting down. Very different between people and interestingly responds differently to overfeeding: some people automatically and significantly increase NEAT when overfed; some do not. The former are very resistant to getting fat, even in a very obesogenic environment; the latter not. As the first link puts it:

Changes in SPA/NEAT can vary hugely and explain most of the discrepancies in expected vs. actual weight gain. In the earliest study, when overfed nearly 1000 calories/day weight/fat gain varied almost 10 fold but this was explained by massive variance in NEAT; some people increased their spontaneous movement by 700 cal/day (making the true surplus 300 cal/day) while one poor person (a woman) had her NEAT go down a little bit (she gained the most fat). This is mostly genetic, unfortunately.

So there is dynamic individual variation in RMR, TEA, and in NEAT that result in faster and slower metabolic rates. TEA is volitional; the other two not so much so.

The higher the metabolic rate, the more food taken in, the easier it is to get at least the minimum RDA for the various micro and macronutrients. Maintaining weight (not gaining), or more so losing weight, with a low metabolic rate means eating little and risking missing hitting those RDA values unless one also eats smart.