I'm curious about how the metabolic rate of these former contestants is determined. Are they confined to a lab where their dietary intake and physical activity

I'm curious about how the metabolic rate of these former contestants is determined. Are they confined to a lab where their dietary intake and physical activity can be accurately measured for an extended period of time? Probably not. My best guess is that the subjects being studied are asked to keep food and activity journals and then these, plus their weight, is used to calculate their metabolic rate. I've experimented with keeping a food journal in the past, and it's exceptionally difficult to keep track of everything you eat without this extra work impacting your food choices. e.g. The chore of writing stuff down might prevent me from casually snagging a handful of nuts on my way through the kitchen, and consciousness about how it will look in the journal might make me pass on those chips. Even ignoring these problems, it takes a lot of effort to produce even remotely useful data. e.g. "I ate a pear." is actually pretty vague. Breed, size, and ripeness all have a pretty big impact on the nutrients you'll get from that pear. You need to weigh everything as a bare minimum. Also, you need to keep the journal all of the time, because if you keep it for just a week or two that sample likely won't be very representative of your normal habits. Likewise, activities are hard to keep track of. With a fairly standard ergometer (such as a Concept2 rower) you can get a reasonable measure of activity level in a workout. Lifting weights, running, walking, etc. are all much, much vaguer. 30 minutes of "moderate jogging" means different things to different people. Most people are likely to overestimate or habitually pad their activities. So, you have a really vague, spitballed idea of what these people are eating and doing, combined with weight gain. Are their metabolisms really slower than expected, or is there a systematic error common to these people in that, after a period of extreme privation (i.e. the competition) in which some of them lost more than a pound a day, they are now underestimating their food intake and overestimating their activity levels? How much can basal human metabolism really vary anyways? If humans can get by on substantially fewer calories, why don't we all typically do this? Where does all the extra energy normal people inefficiently burn off go?