What to snack while you are on a diet. Snacking for weight loss.

No matter how much you love either, there are only so many you can eat. That's because grapes are super sweet and walnuts are even more filling. A cup of grapes and a handful of walnuts together are a power-combo of natural sugars, fiber, healthy fats, and protein—all of which make for more long-lasting energy.

Grapefruit’s "diet food" rep might be justified: one study found that when people simply ate grapefruit with each meal, they lost up to 3 1/2 pounds over three months. Grapefruit may help manage appetite by lowering insulin levels, say researchers.

"Almost any fruit is going to make a great snack, but you usually want to pair it with a bit of protein to make it more satisfying," says Bowerman; "unlike carbohydrates, which get used up relatively quickly, protein will help sustain your energy and hunger levels for a couple of hours."

Our pick for a protein-fruit pairing: one large apple and one cup of skim milk. This duo will give you 10 grams of protein and 5 grams of fiber for just over 200 calories.

A cup of edamame meets one-third of both your daily fiber and protein needs. If you want them to last longer, suck them straight from the shells. Research published in the journal Appetite shows you feel like you have eaten more if you can see the remnants (in this case the pods) of your food.