You know some lucky individuals who can seemingly eat anything under the sun yet not gain weight (as in fat mass).
I have a few hypotheses why this is the case. The usual story is they have a “high metabolism” or they’re “young”, and there is some truth to this.
However, this is my #1 reason why the “eat so much and stay so thin” phenomenon exists:
1. The lean person simply hasn’t seen the result of eating a lot.
That’s it. Whether the person under scrutiny is starting out lean or is currently in a lean state, observing that person’s eating habits in the present moment is not an indicator of what got them there, and certainly not where they’re going.
Imagine two opposite ends of the dieting spectrum:
1. An overweight individual who is interesting in losing fat adopts a calorie restricted diet. Because fat loss takes time, visible results will come slowly so even though they are eating less, it may seem like the diet is not working and smaller portions are just keeping them fat.
2. On the flip side, if a very lean individual (at the end of a diet) begins eating like a sumo wrestler, a casual observer would put the two together and it wouldn’t make sense. How does this person shovel it in and not have significant fat mass?
Simply, the overeating hasn’t done its “damage” yet. Even immediately after a big meal, a person with a full set of abs will still have a full set of abs, just bloated. The food hasn’t yet worked its way through the digestive system to be stored as fat. Furthermore, you don’t know how that person eats when you’re not observing them, and in a very extreme case they may very well be fasting and/or exercising like an Olympic athlete when they’re not scarfing down mega calories.
There is also the perceptual distortion of what people look like in clothes. As a general rule, you can hide a lot in clothing than you can without.
I’m not denying that some people have a higher metabolism, but this is a rare exception. And a high metabolism is not necessarily a desirable trait, despite what some people might believe; an inefficient digestive system is less apt to utilizing nutrients for general growth and repair. Talking to a doctor or nutritionist is the first priority in this case.