We have all heard about superfoods and their impact on our health, but do you ever wonder which are the healthiestsuperfoods? Jennifer Di Noia of William Paterson University decided to find out which fruits and vegetables had the highest nutrient content, and her results were recently published in the Centers for Disease Control’s Preventing Chronic Disease.

TIME has details of the study:

Di Noia focused on 17 nutrients considered by the food experts at the United Nations and the Institute of Medicine to be important to good health and to lowering risk of heart disease and cancer: potassium, fiber, protein, calcium, iron, thiamin, riboflavin, niacin, folate, zinc, and vitamins A, B6, B12, C, D, E, and K.

She then combed the scientific literature to calculate how many nutrients they contained per calorie of energy they provided (based on a 2,000-calorie-per-day diet); the higher the value, the more of a powerhouse food it was.

To give you an idea of how to interpret scores, watercress scored a perfect 100 (meaning you get 100% of essential vitamins and minerals from one 100-gram serving), while white grapefruit (which scored the lowest of the foods she examined) got a 10.47.

Below you can find the 10 foods with the highest nutrient density scores and see which foods give you the most nutrient bang for your buck.

(Spoiler alert: this will make you want to eat your greens!)

Parsley

Nutrient Density Score: 65.59

Parsley is rich in many vital vitamins, including Vitamin C, B 12, K and A. This means parsley keeps your immune system strong, tones your bones and heals the nervous system, too. It helps flush out excess fluid from the body, thus supporting kidney function

Collard Greens

Nutrient Density Score: 62.49

The cholesterol-lowering ability of collard greens may be the greatest of all commonly eaten cruciferous vegetables. In a recent study, steamed collard greens outshined steamed kale, mustard greens, broccoli, Brussels sprouts, and cabbage in terms of its ability to bind bile acids in the digestive tract. When this bile acid binding takes place, it is easier for the bile acids to be excreted from the body. Since bile acids are made from cholesterol, the net impact of this bile acid binding is a lowering of the body’s cholesterol level. It’s worth noting that steamed collards show much greater bile acid binding ability than raw collards.

We get unique health benefits from collard greens in the form of cancer protection. The cancer-preventive properties of collard greens may be largely related to 4 specific glucosinolates found in this cruciferous vegetable: glucoraphanin, sinigrin, gluconasturtiian, and glucotropaeolin. Each of these glucosinolates can be converted into an isothiocyanate (ITC) that helps lower our cancer risk by supporting our detox and anti-inflammatory systems.

Leaf Lettuce 

Nutrient Density Score: 70.73

Vitamins in lettuce are plentiful. Its fresh leaves are an excellent source of several Vitamin A and beta carotenes. Just 100 g of fresh, raw-lettuce provides 247% of daily vitamin A, and 4443 µg of beta-carotene. These compounds have antioxidant properties. Vitamin A is required for maintaining healthy mucus membranes and skin, and is also essential for vision. Consumption of natural fruits and vegetables rich in flavonoids helps to protect the body from lung and oral cavity cancers.

It is a rich source of vitamin K. Vitamin K has a potential role in the bone metabolism where it thought to increase bone mass by promoting osteotrophic activity inside the bone cells. It also has established role inAlzheimer’s disease patients by limiting neuronal damage in the brain.

Fresh leaves contain good amounts folates and vitamin C. Folates are part of co-factors in the enzyme metabolism required for DNA synthesis and therefore, play a vital role in prevention of the neural tube defects in the baby (fetus) during pregnancy.

Vitamin C is a powerful natural antioxidant; regular consumption of foods rich in vitamin C helps the body develop resistance against infectious agents and scavenge harmful, pro-inflammatory free radicals.

Lettuce leaves are one of the very low calorie green-vegetables. 100 g fresh greens provide just 15 calories.Nonetheless, they are the store house of many phyto-nutrients that possess health promoting and disease prevention properties.

Romaine Lettuce

Nutrient Density Score: 63.48

Not all lettuce is created equal, but if you start your meal with a salad made of romaine lettuce you will be sure to add not only a variety of textures and flavors to your meal but an enormous amount of nutritional value. Most of the domestic U.S. harvest of romaine lettuce and other salad greens comes from California and is available throughout the year.

Lettuce is synonymous with salads as they are predominantly made from crispy green lettuce leaves. Most varieties of lettuce exude small amounts of a white, milky liquid when their leaves are broken. This “milk” gives lettuce its slightly bitter flavor and its scientific name, Lactuca sativa derived from the Latin word for milk.

Due to its extremely low calorie content and high water volume, romaine lettuce—while often overlooked in the nutrition world—is actually a very nutritious food. Based on its nutrient richness, our food ranking system qualified it as an excellent source of vitamin A (notably through its concentration of the pro-vitamin A carotenoid, beta-carotene), vitamin K, folate, and molybdenum. Romaine lettuce also emerged from our ranking system as a very good source of dietary fiber, four minerals (manganese, potassium, copper, and iron), and three vitamins (biotin, vitamin B1, and vitamin C).

Chicory

Nutrient Density Score: 73.36

Chicory is a woody, herbaceous plant that has a wealth of health benefits, including the ability to ease digestive problems, prevent heartburn, reduce arthritis pains, detoxify the liver and gallbladder, prevent bacterial infections, boost the immune system, and reduce the chance of heart disease. It is also a natural sedative, and can protect against kidney stones, and benefit attempts to lose weight. All in all, this small plant is a powerful addition to any diet.

Spinach

Nutrient Density Score: 86.43

We all know that Popeye made himself super strong by eating spinach, but you may be surprised to learn that he may also have been helping to protect himself against inflammatory problems, oxidative stress-related problems, cardiovascular problems, bone problems, and cancers at the same time.

Among the World’s Healthiest vegetables, spinach comes out at the top of our ranking list for nutrient richness. Rich in vitamins and minerals, it is also concentrated in health-promoting phytonutrients such as carotenoids (beta-carotene, lutein, and zeaxanthin) and flavonoids to provide you with powerful antioxidant protection.

Beet Greens

Nutrient Density Score: 87.08

A recent study has shown beet greens to be a major contributor in many diets to total intake of the carotenoids lutein and beta-carotene. While not as concentrated in lutein as collard greens or spinach, beet greens have nevertheless been shown to be an outstanding source of this key carotenoid. (Lutein is known to play an especially important role in eye health, including the health of the retina.)

Besides supplying good amounts of protein, phosphorus, and zinc, beet greens are also a great source of fiber. Packed with antioxidants, they’re high in vitamin B6, magnesium, potassium, copper, and manganese, and low in fat and cholesterol. Based on a 2,000 calorie diet, daily values of beet greens contain: 220% of vitamin A, 60% of vitamin C, 16% of calcium, and 15% of iron.

Chinese Cabbage

Nutrient Density Score: 91.99

Chinese cabbage has long been recognised as a health boosting vegetable. This leafy vegetable, often used in the Chinese cuisine contains calcium and potassium, which are used by the body to regulate blood pressure. When you combine this with Chinese cabbage’s low sodium content, you get a vegetable that is well suited to supporting your cardiovascular system. The combination of vitamins, especially vitamin C, are used by the body to boost and maintain a healthy immune system. The high nutrition and low calories found within the slow juice of Chinese cabbage make it an ideal aid to healthy weight loss. Chinese cabbage contains antiseptic and antibacterial properties, helping fight off unwanted organisms within the body.

Chard

Nutrient Density Score: 89.27

Swiss chard is a nutritional powerhouse — an excellent source of vitamins K, A, and C, as well as a good source of magnesium, potassium, iron, and dietary fiber. Swiss chard rainbow: The thick stalks are red, white, yellow, or green.

Watercress

Nutrient Density Score: 100

An ancient green said to have been a staple in Roman soldiers diets, watercress is actually a part of the cruciferous (also known as brassica) family of vegetables along with kale, broccoli, arugula and Brussels sprouts. Watercress is very low in calories, but contains phytonutrients like isothiocyanates and antioxidants with a plethora of disease-preventive properties. Gluconasturtiin, a glucosinolate compound providing the peppery flavor, is one of them, contained in the leaves and stems and providing phenethyl isothiocyanates, shown to inhibit carcinogens. Eating watercress daily has the ability to significantly reduce DNA damage to blood cells and further to resist DNA damage caused by free radicals, according to a two-year research project at the University of Ulster.