Downfalls of eating peanut butter after a workout?

First off it's impossible to "gain" back fat burned from exercise from just eating a simple snack. No, peanut better will not effect you in weight wise. It isn't the smartest decision, you want to eat protein after working out so it can help your muscles, you want to eat carb food like bread and fruit before exercising for carbs for energy.

Peanut butter really isn't high in protien you would have to eat nearly half a jar to get a good amount digested. The bioavailabilty of peanuts isn't the best either. Its only about 88% where as chicken is95 eggs are98% and whey is 99%. 80 percent of saturated fats are burned as medium chain triglycerides which are burned as energy. Find a better source.

peanut butter is great after a workout due to the protein.

NO! no longer well being. the place are your vegetables? the place are the culmination? all i see is sugar-loaded proteins, and carbs. and undesirable carbs, too. and basically slightly dairy. terrible, terrible weight loss application.