Two of those five servings must be fruit – the other three should focus on vegetables, the study found.
“This amount is likely to offer the greatest benefit in terms of preventing major chronic diseases and is a relatively reachable 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 vegetable in question.
“We also found that not all fruits and vegetables offer the same degree of benefit, although current dietary recommendations generally treat all types of fruits and vegetables, including starchy vegetables, fruit juices and potatoes, in the same way,” he said. Wang.
Peas, corn, potatoes and other starchy vegetables, for example, have not been associated with a reduced risk of death or specific chronic diseases.
Green leafy vegetables rich in beta-carotene and vitamin C, such as spinach, lettuce and cabbage, along with carrots, have shown benefits.
“The totality of evidence in the study” should convince health professionals to promote the consumption of more fruits and vegetables as a fundamental dietary strategy, and for citizens to adopt this, “wrote Dr. Naveed Sattar and Dr. Nita Forouhi in a accompanying editorial to be published in April.
Sattar is a professor at the Institute of Cardiovascular and Medical Sciences at the University of Glasgow; Forouhi leads the nutritional epidemiology program at the MRC Epidemiology Unit at the University of Cambridge. None of them were involved with the new study.
“The biggest gains can come from encouraging those who rarely eat fruits or vegetables, since diets rich in even more modest consumption of fruits and vegetables are beneficial, “they wrote.
Association, without cause and effect
The study, published on Monday in AHA’s Circulation magazine, was large and divided into 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 completed a questionnaire on eating habits at the beginning of the studies; these questionnaires were updated every two to four years. This information was then compared to the health and death records collected during long-term studies.
The second part of the study was a meta-analysis of grouped data from 26 studies covering almost 2 million participants from 29 countries and territories in Asia, Africa, Australia, Europe and South and North America. These studies also compared self-reported consumption of fruits and vegetables with mortality rates.
People who ate five servings of fruits and vegetables daily had a 13% lower risk of death from any cause than people who ate only two servings of fruits 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 diseases, such as chronic obstructive pulmonary disease (COPD) than those who ate only two portions, the study found.
Only five servings?
Strangely, the study found no benefit in prolonging life by eating more than five servings of fruits and vegetables a day, which is contrary to previous research on animals and people.
“From eight to nine servings a day we saw the best effect (on immunity),” said the study’s author, Dr. Simin Meydani, senior scientist and leader of the nutritional immunology team at the Human Nutrition Research Center Jean Mayer USDA from Tufts University on Aging.
Meydani pointed out that the new study was based on self-reported food intake, which relies 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 based mainly on observational studies and food intake records, which I do not believe have the sensitivity to differentiate and pinpoint the exact dose required,” said Meydani, who was not involved in the study.
“In order to recommend that five servings of fruits and vegetables are the best dose, they will need to do a randomized clinical trial that looks at disease outcomes or health biomarkers, which has not been done systematically,” said Meydani.
Few of us eat our fruits and vegetables
Dietary guidelines say that adult women should eat at least 1.5 cups of fruit and 2.5 cups of vegetables a day. Men need more – 2 cups of fruit and 3.5 cups of vegetables a day.
“The American Heart Association recommends filling at least half of your plate with fruits and vegetables at each meal,” said Dr. Anne Thorndike, who chairs the American Heart Association’s nutrition committee, in a statement.
“This research provides strong evidence of the lifelong benefits of eating fruits and vegetables and suggests a target amount to be consumed daily for optimal health,” added Thorndike, who is also an associate professor of medicine at Harvard Medical School.