Many bars are formulated for athletes as a quick way to deliver the protein they need to build muscle, which is why this super-nutrient is the star ingredient in most brands. It also feeds the calorie-burning furnace known as your metabolism and hushes between-meal hunger pangs because it's digested more slowly than other nutrients.
Look For: At least six grams. Emerging research indicates that whey, a dairy-derived protein, may have a slight advantage over other forms of protein when it comes to body sculpting. And according to a study that was published in the Journal of Nutrition earlier this year, whey can also help blast belly fat and reduce overall body weight.
Don't be afraid of them! Carbs provide you with quick energy and replenish lost glycogen (stored sugar that fuels exercise) after a tough workout, and they also play a role in insulin secretion, which helps your muscles soak up the amino acids they need in order to repair and rebuild themselves.
Look For: Whole grains and dried fruit (35 grams or less of total carbs, of which no more than 19 grams should be from sugar). Steer clear of tough-to-digest sugar alcohols that can lead to rather unpleasant tummy issues, says Heller.
If you want your thighs to be fat-free, your bar shouldn't be. A little healthy fat is what helps boost bar flavor, and it helps keep you full too, says Heller.
Look For: Heart-healthy unsaturated fats that come from nuts, seeds, and peanut butter (eight grams or less). They satisfy your stomach without clogging your arteries the way many saturated fats, such as palm oil, do.
Considering that most of us get only about 15 of the 25 grams of fiber we need each day, sneaking in a few extra grams can help fill the void—and your tummy. Because your body can't digest fiber, it helps you feel full, and studies have linked a high-fiber diet to a longer life span, reduced risk for breast cancer, and other health benefits.
Look For: Up to five grams of any kind. Most bars don't identify the type of fiber they contain, but many have some combo of insoluble and soluble fiber, both of which take up space in your digestive tract to keep you full.
Vitamins and Minerals
The back of a wrapper can read much like the label on a bottle of multivitamins: Many bars are rich in antioxidants and contain important nutrients like potassium, iron, folate, and vitamins A, C, and D.
Look For: Calcium. This essential mineral is critical for bone health and muscle function, so it can enhance your workout and may help torch fat and prevent stress fractures. People have a tough time getting enough C from food alone, so it's a bonus to have it in your bar.