I use to avidly eat protein bars(like 2-4 a day), but I have not ate more than 4 in the last 2 months. Through my experience with them, I have found, that sometimes when I eat bars instead of real food , I end up eating less calories, but this depends on the bar and the real food I plan to eat. For example, late night, there were times when I would feel content after eating 1 designer protein bar(250 calories), but I would need to eat 700 calories from nuts and tuna to acheive the feeling of content. Even when this is the case, I prefer real food because it allows me to know exactly what I am eating and usually real-food is healthier(i.e no trans,saturated fat,hydro. oils,high GI carbs). I am not sure about this, but I also think that generally real food(as long as its low GI carbs,fats, or protein) does not cause as much insulin activity. As a general rule, I do not eat any processed (carb) foods(except post-workot), or nutrition(including low-carb/protein) bars. If I only had the option of eating a protein bar or sweets, I would definetly eat the protein bar.