Scientist busts myths about how humans burn calories

Let's consider a specific example: Lactose intolerance. The Wiki page for it is pretty good. So, despite the name, lactose intolerance refers to lacking the enzyme lactase, which is used to break down lactose. If you have lactase, then your human cells can use the calories from lactose; if you don't, then the bacteria get the lactose. Wiki says "Symptoms may include abdominal pain, bloating, diarrhea, gas, and nausea", which sounds like the bacteria do indeed eat it; if the bacteria couldn't extract calories from it either, then I assume it would just pass through and there would be no symptoms.

Thus, if Bob and Joe eat the exact same diet that has some milk products, and Bob is lactose intolerant while Joe isn't, then Bob's cells get fewer calories from that diet than Joe's. If Bob and Joe's bodies are otherwise identical and follow identical exercise routines, then I would assume that, like, if the diet is exactly enough to maintain Joe's weight, then Bob would lose weight; and if it's exactly enough to maintain Bob's weight, then Joe would gain weight. (Right? For sake of illustration, we could imagine that most of the diet's calories are from milk, and assume Bob can tolerate the nausea.) Yet "calories in" (measured as food entering stomach) are identical, and "calories out" (measured as CO2) might also be identical.

Lactose is a specific, well-understood example of some people absorbing nutrients much better than others. I think there are other examples, and I expect there's a lot of variation in absorption efficiency that's less known. When you hear about people who eat lots of food and remain thin, I suspect this is part of the explanation. And whether their bacteria get the calories instead, or whether it passes through untouched, might show up in CO2 measurements but I don't think it would be related to body fat accumulation.

In a conservation-of-energy sense, "calories in" certainly gives you an upper bound on how many observed "calories out" you can produce without losing weight. But I don't think there's a lower bound on how inefficient someone's digestive system can be (except "zero"), or a practical upper bound on how much their cells might burn energy without us noticing (without close observation). I think, if you wanted a complete accounting of calories-out that would actually match the input, you'd need to add up (a) the heat a person puts out (via contact with air and surfaces, also infrared emissions), (b) the work they do in a physics sense (e.g. lifting heavy objects), and (c) the amount of un-burned calories in their stool (or any other excreted substances).

Based on your description, I will venture a guess that you are not obese / grossly overweight. There is good evidence from various studies that obese/overweight people are not typically able to achieve this - usually their craving for food is far too powerful to just control simply by falling into a routine; or, the body sometimes finds other ways to adjust (the lipostat model).

This is really the problem with CICO - it is definitely correct in an abstract sense (weight doesn't come from thin air, and neither does food you eat magically disappear), but the factors controlling calories in and calories out are far more complex. Human behavior is far from being entirely rationally determined. Our choices (particularly in regards to food, exercise, and other basic needs) are to a great extent controlled by our metabolism, even though it often doesn't seem that way.

This probably explains why people rarely lose weight on the long term - you can allow yourself to be forced to eat less than your body thinks it needs for a while, and obviously you'll lose weight; but you will go right back up to your "normal" weight as soon as the forcing stops (program ends, willpower exhausted etc).

Of fine running alone might not help you to lose weight. Also there might be a feedback loop to not eat too much crap for a serious runner. E.g. running with less weight is just more fun :-) But does that mean other activities where you gain muscle mass would not help to keep your weight in an acceptable range? I could be very well the case that burn more energy because you have more muscles.

> when adjusted for nonfat body mass

> when adjusted for fat-free body mass

The article is not cheating, but it's not underlining this bit which is essential. It's talking about aerobic exercise, which means "trying to run your way to being thin doesn't work". Which may be news for some people on HN from what I see, but is far from being new or controversial.

On the other hand, building muscle gives you a perpetual "eat more" card. It permanently increases your fat free mass, and thus your TEE. I haven't heard anything about a similar increase in appetite - if anything, bodybuilders struggle to eat enough calories. So, boys and girls, definitely hit the gym. Just stay away from the stepper and pick up some weights. Also don't forget protein intake when you do that.

I'm really having a hard time reading this. They lost me even before, when they said he likes hiking and he's not fat. Good science can come from the worst people. Show me the data, no need to sell me the authors.