How to lose fat without losing muscle
Three things decide whether the weight you lose is fat or muscle: protein at roughly 1.6 to 2.2 grams per kilogram of body weight, resistance training at least twice a week as the signal that muscle is still needed, and losing no more than about 1% of body weight per week. Drop any one of them and the balance tips toward muscle immediately.
"Losing weight" and "losing fat" get used interchangeably, and they are not the same thing. The scale reports that total mass fell; it says nothing about what left.
How much of the weight lost is fat?
It depends entirely on what you did while losing it. In someone who simply eats less, without resistance training and with low protein, the fat-free share of the loss can be as high as a third. In someone doing all three of the things below, it is far lower.
This matters because muscle is the tissue that burns energy. Losing it means lower daily expenditure, which makes the next attempt harder than this one.
How much protein do you need?
Morton and colleagues (2018), pooling 49 trials across 1,863 people, found the benefit to lean mass rising with protein up to about 1.6 grams per kilogram of body weight per day, then flattening.
In a deficit, most recommendations move up to 1.8 to 2.2 grams, because a body short of energy is more willing to pull protein into use as fuel.
Why does resistance training matter more than cardio here?
Because it is a signal, not just calories burned. The body does not maintain tissue it is not using, and during a deficit unused muscle is the first thing considered for breakdown. Lifting is how you say it is still needed.
Two or three sessions a week covering the major muscle groups is enough for this purpose. It does not have to be a bodybuilder's programme.
Can you lose fat from one specific place?
No. Training a muscle does not make the fat above it disappear first. The order in which fat leaves is set largely by genetics and hormones, and it is not something you get to choose.
A hundred sit-ups a day builds abdominal muscle; it does not tell abdominal fat to go first. What you can do is lower total body fat, and the place you care about arrives in its own order.
What has sleep got to do with the ratio?
More than most people expect. Nedeltcheva and colleagues (2010) held 10 people at the same energy deficit for 14 days, varying only sleep — 5.5 versus 8.5 hours. The short-sleep group lost about 55% less fat and about 60% more fat-free mass.
It is a small study and should be read carefully, but its direction matches what has come since, and it is a variable you can change without altering a single thing about the food.
Reading something you can act on beats reading something you cannot.