A new study affirms long-standing nutritional guidelines on how eating five servings of fruits and vegetables can help people live longer. But it also adds some insights on precisely which fruits and vegetables are beneficial, and which are merely "neutral."
In a new study published in Circulation, Dong Wang, a faculty member at Harvard Medical School and Brigham and Women's Hospital, and colleagues examined the optimal intake of fruits and vegetables for long-term health. They followed two prospective cohort studies of more than 100,000 U.S. residents over a 30-year period. The researchers then conducted a dose-response meta-analysis of those two studies, along with 24 other cohort studies conducted around the world. Overall, the research involved more than 1.8 million participants.
According to the study in Circulation, serving size varied across the cohort studies reviewed, but the researchers for the dose-response meta-analysis "converted fruit and vegetable intake in grams into servings using 80g as a standard serving size." In comparison, the Dietary Guidelines for Americans categorizes one serving of fruits or vegetables ranges as two cups of leafy salad greens, one cup of raw or cooked vegetables or fruit, one cup of vegetable or fruit juice, or half a cup of dried fruits or vegetables.
Study: More fruits and vegetables, longer life—up to a limit
Overall, the researchers found that people who ate a mix of two servings of fruit plus three servings of vegetables per day (for a total of five servings) had "a 13% lower risk of all-cause death compared to people who eat two servings of fruit and vegetables per day," Wang said, although he noted the study proved correlation, not causation.
In addition, people who consumed two servings of fruit plus three servings of vegetables per day also had a 35% lower fatality risk from respiratory disease, a 12% lower fatality risk from cardiovascular disease, and a 10% lower fatality risk from cancer, when compared to people who ate just two servings per day.
Interestingly, however, the study found that consuming more than five servings of fruits and vegetables per day did not correlate with additional benefits. Risk reduction appeared to plateau at five servings per day, a Washington Post article about the study reports. That said, eating more than five servings of fruits and vegetables wasn't associated with any increase in overall mortality risk, according to Wang's study. In addition, other research has suggested that more than five servings could be linked to disease prevention, according to the Post.
In comparison, however, most Americans typically consume just one daily serving of fruit and one-and-a-half daily servings of vegetables. That’s well below the quantity recommended by Dietary Guidelines for Americans, which is up to nine servings per day, or by the amount recommended by Wang, et al., in their recent study, the Post reports.
The fruits and vegetables that don't make the cut
The study also found that while nearly all fruits and vegetables—including leafy greens, citrus, and berries—were linked with lower overall mortality, there were a few foods that weren't. Specifically, the researchers found that fruit juices and starchy vegetables—including corn, potatoes, and peas—were not linked to a reduced risk of death or chronic disease, potentially because these fruits and vegetables have a more significant effect on blood sugar levels.
However, the study didn't indicate that consuming fruit juice or starchy vegetables increased anyone's risk of mortality either—they simply didn't appear to reduce their mortality risk. As the Post’s Cara Rosenbloom put it, "Consider them neutral."
Nonetheless, by distinguishing between those types of fruits and vegetables and others, the study differed from the Dietary Guidelines for Americans, according to the Post, which currently categorizes all fruit and vegetable consumption equally—even fruit juice (Searing, Washington Post, 3/7; Rosenbloom, Washington Post, 3/18).