People feel better on meat-only diets because they stop eating junk food, not because meat is special.

The metabolic improvements observed during initiation of very-low-carbohydrate or carnivore diets are primarily attributable to caloric restriction and elimination of ultra-processed foods, not to the physiological effects of animal product consumption alone.

Eating fewer carbs and calories helps overweight people lose weight by improving how their bodies process energy. This finding is from the abstract summary - full study details were not available

Eating only animal products might help balance your hunger hormones so you naturally eat less and lose body fat, especially if you're overweight.