A convincing report at Mosaic Science explains why the calorie is a pretty terrible tool for losing weight. Calorie counts on nutrition labels are really fuzzy guesses, and they don’t take into account how food is prepared, which plays a huge part in how much energy we get from it. Think of a frying pan as an exterior stomach—food cooked at a higher temperature is easier to digest, meaning a well-done steak is more fattening than a rare one. But perhaps more important, the germs in our guts play a significant role in how we digest food, even if that role is not yet well understood.
A 2013 study found human twins in which one was obese and one was thin, then transplanted their gut microbes into mice. Mice who got the obese twin’s microbes gained weight, while the others did not—even though they were fed the same diet. Further, a woman “gained more than 40 lbs after receiving a transplant of gut microbes from her overweight teenage daughter.” Nothing else changed about her.
That scientists don’t yet know which microbes affect weight yet doesn’t matter; diet fads do not wait for science. This is why I believe that we will soon see premium services that offer to transplant gut microbes from thin people into people who want to lose weight. It meets an important criteria for diet fads: so gross that people assume it must work, otherwise no one would do it.