We read the studies. You get the answers.

You could find out whether olive oil increases your testosterone with two blood tests and a bottle you probably already own. A morning test comes first, for a starting number on paper. The butter goes after that, olive oil takes its place in everything you cook, and a few weeks go by. A second test at the same early hour gives you a before and an after, and a higher second number would be all the proof you need. Testosterone came back about 17 percent higher, probably the very number you have seen quoted, when young men went through almost exactly that experiment. They even spent two weeks on butter before the switch.

Off come the rules, the food scale back into its drawer, the calorie app left unopened for a week, the Friday dinners out allowed back onto the calendar, the dessert rule quietly retired, until a single habit from the diet is still standing because you decided it stays, and that habit is protein. Protein earned that spot. Through the hungriest weeks, the meals built around it were the ones that carried you to the next meal, and the maintenance advice you keep reading says to hold it high. What you want settled now is whether a high protein diet actually helps you keep weight off, or only helped you take it off.

A fast is an empty stretch in the day rather than a switch the body keeps flipped on, and the emptiness does most of the work.