Eating more fruits and vegetables was associated with less mortality in large observational studies, but there was a ceiling on how much these foods could improve health.
Nonlinear inverse associations of fruit and vegetable intake with mortality risk over 30 years turned up in two well-known prospective studies with more than 100,000 participants in total.
The widely promoted “five-a-day” was, in fact, better than two servings per day in terms of:
- Total mortality: HR 0.87 (95% CI 0.85-0.90)
- Cardiovascular disease mortality: HR 0.88 (95% CI 0.83-0.94)
- Cancer mortality: HR 0.90 (95% CI 0.86-0.95)
- Respiratory disease mortality: HR 0.65 (95% CI 0.59-0.72)
Two servings per day of fruit and three of vegetables conferred the greatest benefit; any more servings than that did not yield additional mortality risk reduction, according to researchers led by Dong Wang, MD, ScD, of Brigham and Women’s Hospital and Harvard Medical School. Their manuscript was published online in Circulation.
Exceptions were starchy vegetables (e.g., peas, corn), fruit juices, and potatoes, which were not associated with decreased mortality over 3 decades in the report.
Similar findings were observed in a meta-analysis incorporating these two studies with 24 other prospective cohort studies with a total of 1,892,885 participants.
“These findings support current dietary recommendations to increase intakes of fruits and vegetables, and that the succinct 5-a-day message is consistent with available evidence,” Wang’s group concluded.
Average consumption in the U.S. is just one serving of fruit and 1.5 servings of vegetables per day, Wang and colleagues noted, despite public health campaigns urging people to eat more of these food items for decades.
“Health professionals cannot change food policy — that is the role of Governments — but they can help people understand how to implement simple dietary changes. 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,” according to Naveed Sattar MD, PhD, of the University of Glasgow, Scotland, and Nita Forouhi, MD, PhD, of the University of Cambridge, England.
Even small but sustainable dietary changes “may be enough for some health gains and could set the foundation for them to try additional adjustments,” the duo wrote in an accompanying editorial.
The greater challenge is how to achieve population-wide dietary improvements, which will require structural changes and national policy level interventions that increase access to healthy foods via subsidies from taxing unhealthy foods, Sattar and Forouhi argued.
For the study, Wang and colleagues included women from the Nurses Health Study (n=66,719) and men from the Health Professionals Follow-up Study (n=42,016) who were free from cardiovascular disease, cancer, and diabetes at baseline. All had had their diet regularly assessed since the 1980s using a food frequency questionnaire.
Investigators adjusted for frequent fruit and vegetable eaters being older, more likely to use multivitamins, and having higher total energy intake, dietary quality, physical activity level, and prevalence of hypercholesterolemia. This group was also less likely to be current smokers and drank less alcohol.
The observational nature of the study left room for residual confounding despite these adjustments. Moreover, Wang’s team cautioned that there was potential for reverse caution (i.e., that people in poor health might change their diets toward a healthier diet) and measurement errors from relying on self-reported food consumption.
“Furthermore, it would have been informative if the authors had taken a more specific look at gastrointestinal-related deaths or cancers. Considering prior concern raised about frozen/canned fruit consumption and mortality, it is important to extend research to examining differences across raw, tinned, frozen, or cooked vegetables,” Sattar and Forouhi added.
“Still, the totality of the evidence … should convince health professionals to promote eating more fruits and vegetables as a key dietary strategy, and for citizens to embrace this,” the editorialists urged.
The study was funded by NIH grants with additional support to Wang from the National Institute of Diabetes and Digestive and Kidney Diseases.
Wang and Forouhi had no disclosures.
Sattar disclosed consulting for or receiving lecture fees from Amgen, AstraZeneca, Boehringer Ingelheim, Eli Lilly, Merck Sharp & Dohme, Novartis, Novo Nordisk, Pfizer, and Sanofi as well as receiving institutional grant support from Boehringer Ingelheim.