I don’t think standard humans measure enough data to check the mass balance of their body’s system. I seem to remember an episode of CSI where that kind of behavior was used as evidence of an eating disorder.
Joking aside, being overweight is mostly about body density, not mass. Few people get upset about having too much lean muscle or the food inputs needed get there; that is a different set of health risks.
Whether your body converts incoming calories to muscle or fat or whatever else does actually depend (to some variable extent) on genetics, along with many other factors. Glossing this as “breaking the laws of physics” is a straw man.
One example off the top of my head: eating lots of protein to build muscle can be hard on the liver.
Exercising a lot is generally healthy, but high impact exercises (running comes to mind) can cause your joints to wear out a lot faster.
This is all also assuming an average, healthy person with no existing medical conditions. Things get trickier if you have exertional asthma, any kind of condition that can cause fatigue, etc.
Joking aside, being overweight is mostly about body density, not mass. Few people get upset about having too much lean muscle or the food inputs needed get there; that is a different set of health risks.
Whether your body converts incoming calories to muscle or fat or whatever else does actually depend (to some variable extent) on genetics, along with many other factors. Glossing this as “breaking the laws of physics” is a straw man.