Many companies now package snacks in 100-calorie portions, but they often don’t contain the nutrients your body needs. "I love the concept of those, but the majority of them aren’t the best options," says Chrissy Wellington, a nutritionist at Canyon Ranch health resort in Lenox, Mass. Some advice: 

Read package labels. Plenty of unhealthy ingredients can go into a 100-calorie snack. Ideally, a serving should contain less than .5 grams of saturated fat and less than 10 to 12 grams of sugar — the lower the better — along with some fiber and protein. Pretzels, air-popped popcorn and nuts tend to be among the healthier packages.

Avoid the least healthy packages. Chocolate chip cookies, candy, biscuits and crackers such as Ritz and Cheez-It land on Wellington’s "worst" list because they’re high in sugar and/or artery-clogging fats.

Think outside the bag. Stay close to 100 calories with 4 to 6 ounces of low-fat yogurt, a hardboiled egg and a small piece of fruit, an ounce of cheese — look for one with less than two grams of fat per serving — or a third of a cup of edamame beans.

Get milk. Drink a cup of low-fat chocolate milk, which is rich in protein, or warm a cup of skim milk with sprinkles of cinnamon and vanilla extract. 

Load up on fruits. A small banana or medium-sized pear or apple should run about 100 calories, as would a cup of berries, half a large grapefruit or two plums or apricots. Or pair half a fruit serving with two teaspoons of peanut butter or a few dry-roasted nuts.

Cut up vegetables. Raw leafy veggies such as broccoli and cauliflower only contain about 30 calories per two cups; other easy snacks such as carrots, celery and cherry tomatoes have roughly 30 calories per half cup. Hummus, at roughly 80 calories for a quarter-cup, can be a smart dip.