Speed up weight loss, boost immunity with these 20 smart foods, drinks

So-called zero-calorie foods, like celery and cucumbers, contain fewer calories than the body uses to break them down. And although nutritionists account for the energy it takes to chew and digest them when they calculate how many calories we need, these eats deserve prime spots on our plates.

You can eat them in large quantities without busting your gut, and low-calorie doesn't mean low nutrients. "And, obviously, if eating very low calorie foods keeps you from eating higher calorie foods, that's a win," says Monica Reinagel, licensed nutritionist and creator of the Nutrition Diva podcast. So fill up your fridge with the following 20 foods that are loaded with vitamins and minerals -- not calories.

Cucumbers

If you're tired of fending off hunger by guzzling glass after glass of H {-2}O, snack on cucumber slices instead. "Eating foods that are high in water can help you feel full at least temporarily by taking up a lot of space in your stomach," Reinagel says. Cucumbers also pack vitamins K and C, potassium and a compound called silica, which helps to build and maintain connective tissue, like muscle, tendons, ligaments and bone.

Citrus fruit

Don't wait until cold season to fill up on oranges, tangerines and grapefruit -- they may help whittle your middle. People with higher vitamin C levels have lower waist-to-hip ratios than those whose bodies contain less of the antioxidant, according to a study published in the American Journal of Clinical Nutrition . What's more, University of Arizona researchers found that those with higher levels of vitamin C oxidized 25 percent more fat during treadmill sessions than those with lower levels of the vitamin.

Celery

Celery delivers serious crunch for next to no calories -- each medium stalk has about 6 -- but it's not shy on nutrients. One cup has a third of your recommended daily intake of vitamin K, along with vitamin A, fiber, folate and potassium. Celery also contains compounds called phthalides, which can relax muscle tissue in artery walls and increase blood flow, thereby helping to lower blood pressure.

Apples

An apple a day keeps your weight at bay! Just make sure to eat the skin. The peel contains most of the fruit's metabolism-boosting fiber, as well as ursolic acid, a compound that may prevent the pounds from piling on, according to a new study from University of Iowa.

Kelp

Don't be squeamish about eating your sea vegetables. Kelp is loaded with vitamin K, which helps keep bones strong, along with a natural fiber called alginate, which may help block fat absorption, according to research from Newcastle University in the U.K. For only 6 calories per 4-ounce serving, try mixing Sea Tangle Kelp Noodles into salads, soups and stir-fries.

Asparagus

A half-cup of cooked asparagus will set you back only 20 calories. Plus, you'll get hefty doses of vitamins K and A, and B vitamins such as folic acid. Since B vitamins play a role in breaking down sugars and starches, eating asparagus may help regulate blood sugar and fend off type 2 diabetes.

Apricots

Brimming with beta-carotene, apricots can help fight cancer and heart disease as well as protect your eyesight. Eating three or more daily servings of fruit rich in vitamins A, C and E and carotenoids like beta-carotene may lower your risk of macular degeneration, the dominant cause of age-related vision loss. When participants in a study published in the Archives of Ophthalmology ate this much fruit they were 36 percent less likely to suffer from the disease compared to those who consumed 1.5 servings or less of fruit daily.

Watermelon

This summertime fruit is loaded with arginine, an amino acid that may aid weight loss. Researchers found that obese mice that were fed arginine supplements burned more fat and gained more lean muscle than those that did not receive them, according to a Journal of Nutrition study.

Tomatoes

The lycopene in tomatoes can protect against prostate cancer and help keep skin looking young by eliminating free radicals that build up when you are exposed to ultraviolet rays. Tip: Cooking tomatoes spikes levels of lycopene and makes it easier for your body to absorb the nutrients, according to a Cornell University study.

Broccoli

Broccoli may be the nation's most-scorned veggie, but it doesn't deserve that reputation. One cup raw contains as much fiber and vitamin C as an orange.

Cauliflower

Counting your carbs? Try boiling, mashing and seasoning cauliflower to get a mashed potato substitute that tastes almost like the real thing. A half-cup of boiled cauliflower contains only 14 calories, but nearly half your daily recommended intake of vitamin C.

Strawberries

One cup of the summertime staple packs more than 100 percent of our daily recommended intake of vitamin C. Strawberries are also one of the most antioxidant-rich fruits you can eat. Compounds called polyphenols may protect your body from the type of cell and tissue damage that is linked to heart disease and certain cancers.

Leafy greens

Whatever variety you pick, you can't go wrong with piling a plate with salad greens. At 4 calories per cup, watercress is loaded with vitamins A, C and K, and a study in

The American Journal of Clinical Nutrition

found that eating 3 ounces of the peppery green daily increases levels of the cancer-fighting antioxidants lutein and beta-carotene. Spinach (7 calories per cup) is brimming with vitamin K, calcium, phosphorus, potassium, zinc and selenium, and contains a hormone that allows muscle tissue to repair itself faster, according to research from Rutgers University.

Red chile peppers

Add a little spice to your cooking and slim down while you're at it. Capsaicin, the compound that gives a red chile pepper its kick, has been shown to help your body burn more calories. Plus, research shows that we tend to eat smaller portions of spicy foods because of the heat.

Mushrooms

Whether you saute them or eat them raw, mushrooms are an often-overlooked superfood. Dutch researchers found that when you digest mushrooms, your body produces cancer-fighting, immunity-boosting metabolites.

Red bell pepper

Any way you slice it, red bell peppers are a great source of nutrients. A medium-size one delivers 250 percent of your daily recommended intake of vitamin C, 75 percent of your daily vitamin A needs and 10 percent of your fiber goals. Chop them up and pair with hummus for a healthy snack.

Summer squash

Whether you love zucchini, butternut or acorn, all squashes are chock-full of vitamins and belly-filling fiber. But summer squash has one advantage: You can eat more of it without gaining weight. In fact, you can have two times more summer squash than winter squash for the same number of calories.

Turnip

The turnip sometimes takes a backseat to more popular root vegetables, like carrots and potatoes, but its nutritional benefits shouldn't be overlooked. The root contains cancer-fighting glucosinolates and is a good source of fiber, calcium and potassium.

Green tea

Whether you prefer it hot or iced, unsweetened green tea is calorie-free and high in an antioxidant called ECGC, which may reduce the risk of heart disease and some cancers while revving up your metabolism. Participants in a Tufts University study who drank the equivalent of three cups of green tea each day lost twice as much weight as those who did not drink the tea. Green tea drinkers also lost significantly more belly fat than non-tea drinkers.

Water

The importance of water can't be overstated. Staying hydrated keeps your metabolism humming, and can keep you alert and energized throughout the day. Drinking two glasses before a meal can also help you keep control over your portions.