While it’s widely known that fruits and vegetables are beneficial for health, a recent Harvard study has identified the top five high-quality options that can significantly reduce the risk of chronic diseases.

In August 2024, researchers published a new study in The American Journal of Clinical Nutrition. The study analyzed data from three large prospective cohorts: the Health Professionals Follow-up Study, the Nurses’ Health Study (NHS), and the Nurses’ Health Study II (NHSII).

The research team conducted a biomarker analysis of 41,714 participants, examining the relationship between the intake of various fruits and vegetables and 14 cardiometabolic biomarkers. They ranked 52 fruits and vegetables based on their metabolic quality.

Top 5 High-Quality Fruits and Vegetables:

• Apples or pears
• Iceberg lettuce
• Raw spinach
• Alfalfa sprouts
• Eggplant or summer squash

On the other hand, the bottom five were peas or lima beans, French fries, watermelon, tomato juice, and corn. In total, the study identified 19 fruits and vegetables with high metabolic quality.

Impact on Chronic Diseases

The researchers analyzed the risk of major chronic diseases in 207,241 participants over a 32-year follow-up period. Key findings include:

• A higher proportion of high-metabolic quality fruits and vegetables in the diet was linked to a lower risk of developing major chronic diseases.
• Participants who consumed a large quantity of fruits and vegetables, but mostly of neutral or low metabolic quality, did not see a reduced risk of chronic diseases. Instead, they showed an increased risk of diabetes.
• In the group with the lowest total fruit and vegetable intake, those with the highest proportion of high-metabolic quality fruits and vegetables had a 15 percent lower risk of major chronic diseases compared to those with the lowest proportion.
• Similar trends were observed for atherosclerotic cardiovascular disease, Type 2 diabetes, and chronic obstructive pulmonary disease. However, cancer did not follow this trend as consistently.

High-quality fruits and vegetables are rich in nutrients like potassium, magnesium, beta-carotene, flavonoids, and dietary fiber, which help lower the risk of chronic diseases through various protective mechanisms, including antioxidant, anti-inflammatory, and antihypertensive effects.

The researchers noted that, beyond focusing on overall fruit and vegetable intake, priority should be given to eating foods with high metabolic quality.

Apples and Pears

Apples and pears share similar nutritional profiles. They are both rich in bioactive compounds such as flavonoids, dietary fiber, and antioxidants, which have been shown to lower the risk of cardiovascular events.

A 2019 systematic review published in Current Developments in Nutrition found that higher consumption of apples, pears, or a combination of both “significantly” reduced the risk of cerebrovascular disease, Type 2 diabetes, cardiovascular and cardiometabolic disease mortality, as well as all-cause mortality.

A 2021 trial published in The American Journal of Clinical Nutrition also showed that, compared to a control group of people who did not eat apples, participants who ate an apple a day for six consecutive weeks showed a 17 percent reduction in C-reactive protein, a biomarker of inflammation in fasting blood, and a 12.4 percent reduction in interleukin-6, a pro-inflammatory cytokine. Additionally, lipopolysaccharide-binding protein (LBP), which helps protect the body from infections caused by gram-negative bacteria such as pneumonia and meningitis, decreased by 20.7 percent.

Spinach

Spinach contains various antioxidants, including flavonoids. Research has shown that flavonoids can effectively prevent lipid peroxidation, a known risk factor for several diseases, including atherosclerosis, diabetes, hepatotoxicity (liver toxicity), and inflammation.

Spinach is also beneficial for brain health. It is rich in two important carotenoids: lutein and zeaxanthin. A study published in the Journal of Alzheimer’s Disease indicated that levels of lutein and zeaxanthin in the brains of Alzheimer’s patients were about 50 percent lower than those in healthy individuals.

People with carotenoid-rich diets, higher levels of lutein and zeaxanthin in their blood, or greater accumulation of these carotenoids as macular pigment in their retinas, had a significantly lower risk of developing Alzheimer’s disease, Kathleen Dorey, the lead author of the study and a professor in the Department of Basic Science Education at the Virginia Tech Carilion School of Medicine, stated in a press release.

Certain green leafy vegetables, such as spinach, peas, and lettuce, are high in lutein and zeaxanthin.

Alfalfa Sprouts

Alfalfa sprouts contain high levels of saponins and other bioactive compounds, which have antioxidant, antiviral, immune-boosting, and antidiabetic properties.

A 2021 study published in the journal Nutrients described the interaction between cholesterol and saponins in animal models as the mechanism underlying the anti-atherosclerotic effects of alfalfa sprouts. (Anti-atherosclerotic properties refer to the ability of a compound to prevent or slow down the development of atherosclerosis, a condition where plaque builds up in the arteries, leading to a narrowing of the blood vessels, increasing the risk of heart attack and stroke.) Alfalfa sprouts are therefore a good dietary source of phytochemicals with anti-atherosclerotic properties.

Eggplant

Eggplant has been shown to improve blood pressure. A randomized, placebo-controlled study involving 100 stressed participants found that consuming eggplant powder improved diastolic blood pressure in people with normal to high blood pressure and reduced both systolic and diastolic blood pressure in those with grade one hypertension. This suggests that eggplant may exert different antihypertensive effects depending on the blood pressure category.

Iceberg Lettuce

Iceberg lettuce is rich in antioxidants, including polyphenols, carotenoids, and vitamin C. One study found that feeding rats a diet with 20 percent lettuce improved lipid metabolism and enhanced plasma antioxidant capacity, thereby offering protection against cardiovascular disease.

Optimal Cooking Methods

The Harvard study noted that cooking methods can influence the nutritional properties of food.

For instance, frying significantly reduces the nutritional value of potatoes and is particularly detrimental to cardiometabolic health, increasing the risk of hyperinsulinemia (when the body produces too much insulin) and inflammation.

A separate study cited by Harvard Medical School found that raw spinach provides the highest amount of lutein compared to traditional cooking methods like boiling, steaming, or pan-frying. The researchers recommended blending or juicing raw spinach to release more lutein, or slicing it for use in salads or sandwiches to achieve a similar benefit.