Food and recipes

I have some leftover russian bear 5000 weight gainer. My question is if I were to add some to my brownie mix, would that help gain and get fat?

Possibly, it could potentially add a lot of calories to your meal, it would be largely from protein though. If you ate the same amount of calories though from a carbohydrate source you would gain more because it would trigger an insulin response, however that path leads to diabetes. So I would say go for it, see how it works for you, calories from protein equal a much healthier gain.