WASHINGTON (CNN) — Five is your new lucky number.
That's how many servings of fruits and vegetables you need to eat each day to live the longest, according to a new study released by the American Heart Association that analyzed data representing nearly 2 million adults worldwide.
Two of those five servings should be fruit — the other three should focus on veggies, the study found.
"This amount likely offers the most benefit in terms of prevention of major chronic disease and is a relatively achievable intake for the general public," said lead author Dr. Dong Wang, an epidemiologist and nutritionist at Harvard Medical School and Brigham and Women's Hospital in Boston, in a statement.
There were differences in benefits, however, depending on the fruit or veggie in question.
"We also found that not all fruits and vegetables offer the same degree of benefit, even though current dietary recommendations generally treat all types of fruits and vegetables, including starchy vegetables, fruit juices and potatoes, the same," Wang said.
Peas, corn, potatoes and other starchy vegetables, for example, were not associated with a reduced risk of death or specific chronic disease.
Green leafy vegetables rich in beta carotene and vitamin C, such as spinach, leafy green lettuce and kale, along with carrots, did show benefits.
In the fruit category, fruits packed with beta carotene and vitamin C, such as berries of all kinds and citrus fruits, also helped reduce risk of death and chronic disease. However, fruit juice did not. Past research has found that it's the fiber in whole fruit that is key to any benefits.
"The totality of the evidence in the study should convince health professionals to promote eating more fruits and vegetables as a key dietary strategy, and for citizens to embrace this," wrote Dr. Naveed Sattar and Dr. Nita Forouhi in an accompanying editorial that will publish in April.
The biggest gains may come from encouraging those who rarely eat fruit or vegetables, since diets rich in even modestly higher fruit and vegetable consumption are beneficial.
–Dr. Naveed Sattar and Dr. Nita Forouhi
Sattar is a professor at the Institute of Cardiovascular and Medical Sciences at the University of Glasgow; Forouhi leads the nutritional epidemiology program of the MRC Epidemiology Unit at the University of Cambridge. Neither were involved with the new study.
"The biggest gains may come from encouraging those who rarely eat fruit or vegetables, since diets rich in even modestly higher fruit and vegetable consumption are beneficial," they wrote.
Association, no cause and effect
The study, published Monday in AHA's journal Circulation, was large and in two parts. The first was an analysis of data from the Nurses' Health Study and the Health Professionals Follow-Up Study, which followed more than 100,000 American men and women for up to 30 years. All participants filled out a food habit questionnaire at the start of the studies; those questionnaires were updated every two to four years. That information was then compared to health and death records gathered during the long-term studies.
The second part of the study was a meta-analysis of pooled data from 26 studies covering nearly 2 million participants from 29 countries and territories in Asia, Africa, Australia, Europe and North and South America. Those studies also compared self-reported fruit and vegetable intake with death rates.
People who ate five servings a day of fruits and vegetables had a 13% lower risk of death from any cause than people who only ate two servings of fruit and vegetables per day.
Eating five servings was also linked to a 12% lower risk of death from cardiovascular disease, including heart disease and stroke.
They also had a 10% lower risk of death from cancer and a 35% lower risk of death from respiratory disease, such as chronic obstructive pulmonary disease than those who ate only two servings, the study found.
5 servings only?
Oddly, the study didn't find any benefit in extending life by eating more than five servings a day of fruits and veggies, which is contrary to prior research in both animals and people.
A 2017 study found a significant reduction in the risk of heart attack, stroke, cancer and early death by eating 10 portions of fruit and vegetables each day. Studies in animals found much lower immune responses in animals who were fed two to three servings of fruits and veggies a day than animals who ate five to nine servings a day.
"The eight to nine servings a day was where we were seeing the best effect (on immunity)," said study author Dr. Simin Meydani, senior scientist and leader of the nutritional immunology team at Tufts University's Jean Mayer USDA Human Nutrition Research Center on Aging.
Meydani pointed to the fact that the new study relied on self-reported food intake, which counts on the participants' ability to remember and be truthful in recording what they ate. Therefore, the new study could only show an association between five servings and better health — not a cause and effect.
"It is mainly based on observational studies and dietary intake records, which I do not believe has the sensitivity to differentiate and pinpoint the exact dose needed," said Meydani, who was not involved in the study.
"In order to recommend that five serving of fruits and vegetables is the best dose, they will need to do a randomized controlled trial looking at either disease outcomes or biomarkers of health, which has not been done in a systematic way," Meydani said.
Few of us eat our fruits and veggies
Dietary guidelines say adult women should eat at least 1.5 cups of fruit and 2.5 cups of vegetables each day. Men need more — 2 cups of fruit and 3.5 cups of vegetables daily.
Yet, only 9% of US adults eat the suggested servings of vegetables, and only 12% eat the recommended amount of fruit, according to the U.S. Centers for Disease Control and Prevention.
"The American Heart Association recommends filling at least half your plate with fruits and vegetables at each meal," said Dr. Anne Thorndike, who chairs of the American Heart Association's nutrition committee, in a statement.
"This research provides strong evidence for the lifelong benefits of eating fruits and vegetables and suggests a goal amount to consume daily for ideal health," added Thorndike, who is also an associate professor of medicine at Harvard Medical School.
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