text: is there such a thing as a high- or low-metabolism and can it effect your weight? you often hear people blaming their metabolism for the fact that they are over-weight. is there any basis of truth in this excuse?  physics taught me that energy cannot be created or destroyed, only converted from one form to another.  so, if two people are eating the same number of calories (and do the same amount of exercise), but one is getting fat (because of a problem with their metabolism) and the other isn't, then how is the fat person managing to do the same amount of work using less energy - thus allowing them to store the excess energy as fat? 'metabolism' just means 'things going on in your body'. rapid metabolism always produces heat as a by-product, just like 'work' does in physics.  unfortunately doctors tend to confuse people by grossly simplifying what goes on in your body.   fat storage is a 'metabolic' process; if your metabolism is fast, you will store more fat. fortunately, the things that increase your 'metabolism' most, will use up some of the storable fat, so there is less to store !  the most 'metabolic' portion of your body is your musculature, although your liver does a wider range of metabolic tasks. (the liver can convert sugar into fat, but only a limited amount, so you do not "store the excess energy as fat".  one problem with the diet/exercise simplification, is that the 'calories' (energy) you eat are not available to use (or store) in your body unless you absorb them through your gut. (shit contains calories that haven't been absorbed; dried shit can be burnt, and is used as fuel in some cultures, although usually it's from livestock rather than humans).  digestion, absorption, and transport of food are all 'metabolic' processes. after you have eaten, your temperature goes up ('thermogenesis') because you are processing the absorbed portion of the food, and moving the unabsorbed food along your gut.   a popular diet (the t-factor diet, book by martin katahn) was based on the various 'thermogenic' (ie. metabolic) effects of different foods.  a common metabolic effect is anxiety-related weight loss, where stress will cause rapid changes. these happen when the muscles (all of them) are more tense because of constant adrenaline production, which also affects appetite and the gut reactions needed to absorb nutrients. so more fuel (mostly fat because the tension is constant and gentle, rather than forceful) is being used, less is being eaten, and a smaller proportion of the nutrients are available. this can all happen without you noticing any difference in your behaviour, unless the stress becomes severe.  the body is operating 24 hours a day, and your conscious movement is only a small fraction of your total activity. hormonal patterns, such as a low or high thyroid output, have an effect on all of your body systems, including motivation. that means you can try hard to overcome the pattern (you still produce adrenaline when thyroid is low, but it takes more effort to do it), but your body will make it even more difficult to remain motivated (it thinks you're dangerously overworking yourself).  the only simple truth is that everybody operates in a slightly different way. 'metabolism' is something that we all have, and we can raise or lower (like blood pressure). that is more difficult for some than for others, but it is not 'the answer' or 'the problem' for anybody.