If you're a middle-aged adult with extra weight, eating either a low-carb high-fat diet or a low-fat diet with fewer calories can help you keep your muscle while losing weight over about 4 months.

If you're overweight and eat less fat for four weeks, you might lose more muscle than fat compared to someone who eats fewer carbs — even if both diets help you lose weight.

Eating fewer carbs and more fat—without counting calories—can help people lose about as much weight as eating less fat and cutting calories. This suggests that what you eat might matter just as much as how much you eat.

If you're overweight and eat fewer carbs instead of less fat for four weeks, you might lose more body fat—even if you lose the same amount of total weight as someone on a low-fat diet.

When people with excess body fat eat very few carbs and more fats, they lose about 4-5% of their muscle mass within a month, and this muscle loss continues for the full 12 weeks of the diet.

If you're overweight and eat fewer carbs instead of less fat for four weeks—without counting calories—you might lose about 8 pounds more than someone on a low-fat diet, and it might be because you're losing more body fat.