A protein bar is a confectionery product built around 20-30 g of protein per 100 g, usually a whey and soy blend held together with syrups, sugar alcohols and fat. It solves one problem well — protein when there is no kitchen — and it is not a health food: energy density sits near chocolate, and the sugar alcohols that keep the label sugar low are what make some bars hard on the gut. Bars vary enormously between brands; the label is worth reading every time.