A new study found an increase in diet-quality scores over 12 years was linked to an 8%-17% reduction in mortality.
Three healthy diets shared common characteristics
People who maintained a high-quality diet over a 12-year period had a significantly lower risk of death than people whose diets were rated low, reported researchers.
According to an analysis of two large U.S. cohorts of health professionals, a 20-percentile increase in diet-quality scores -- an indication of an improved quality of diet -- was linked to an 8%-17% reduction in mortality, reported Mercedes Sotos-Prieto, PhD, of Harvard T.H. Chan School of Public Health in Boston, and colleagues.
Conversely, worsening diet quality over the 12-year period was associated with an increase in mortality of 6%-12%, they wrote in the New England Journal of Medicine.
The risk of death from any cause was significantly lower, by 9%-14%, among people who maintained a high-quality diet than among those who had consistently low diet scores over time.
"This is the first study to demonstrate that improvement in diet quality over time is associated with reduced risk of total and cardiovascular mortality," Sotos-Prieto told MedPage Today. "Previous studies have found that a higher diet quality score is associated with lower mortality, but none of those studies have examined dynamic changes in diet quality over time and subsequent risk of mortality.
"Overall, our findings support the recommendations of the 2015-2020 dietary guidelines, which recommend several healthy eating patterns. It is not necessary to conform to a single dietary plan to achieve a healthy eating pattern."
The researchers examined data on 47,994 women in the Nurses' Health Study and 25,745 men in the Health Professionals Follow-up Study from 1998 through 2010.
Changes in diet quality over the preceding 12 years were assessed with the use of the Alternate Healthy Eating Index–2010 score, the Alternate Mediterranean Diet score, and the Dietary Approaches to Stop Hypertension (DASH) diet score.
At baseline and every 4 years thereafter, the participants completed validated food frequency questionnaires with information on diet. Information on lifestyle and risk factors for cardiovascular disease -- including smoking status, use of aspirin, oral contraceptives, and diabetes -- was assessed and updated every year.
The researchers used Cox proportional-hazards models to calculate the adjusted hazard ratios for total and cause-specific mortality.
The results showed that in the Alternate Healthy Eating cohorts, people with a greater increase in diet quality were younger, had a lower baseline diet score, engaged in more physical activity, and consumed less alcohol than participants with little change in diet quality.
Similar patterns were observed in the Alternate Mediterranean Diet and DASH groups where people who reported consistently higher diet quality were older, had a lower body-mass index, were less likely to be current smokers, and were more physically active than those with a poor diet quality both at baseline and 12 years later.
The pooled hazard ratios for all-cause mortality among people with the greatest improvement in diet quality (13%-33% improvement), as compared with those who had a relatively stable diet quality (0%-3% improvement), in the 12-year period were as follows:
Conversely, compared with no change in diet quality, a decrease in diet quality was associated with increased total mortality: pooled HR 1.12 (95% CI 1.05-1.19), 1.06 (95% CI 0.99-1.13), and 1.06 (95% CI 1.00-1.12), respectively, for the three diet types.
Among people who maintained a high-quality diet over the 12-year period, the risk of death was lower by 14% (95% CI 8%-19%) when assessed with the Alternate Healthy Eating Index score, 11% (95% CI 5%-18%) with the Alternate Mediterranean Diet score, and 9% (95% CI 2%-15%) with the DASH score than those who had consistently low diet scores during that same period.
The researchers concluded that the findings have important implications for informing policy guidance and strategies to sustain a healthy diet over time among middle-aged men and women. And while previous guidelines have put greater emphasis on overall diet quality, "the current evidence indicates that healthy dietary patterns share most of the common characteristics, including higher intake of fruits, vegetables, whole grains, nuts, and legumes, and lower intakes of red and processed meats, sugar-sweetened beverages, and highly refined grains," said Sotos-Prieto.
She explained that while her team could not assume a causal relationship, the very long follow-up of the cohorts allowed the team to examine the changes in diet quality and subsequent risk of mortality for analyses that are "more robust than traditional analyses using baseline or updated diet quality."
Study limitations noted by the researchers included the potential for measurement errors and the limited generalizability, since participants were mostly white health professionals.
The study was supported by the National Institutes of Health.
Sotos Prieto received grants from Fundacion Alfonso Martin Escudero. The senior researcher, Frank Hu, received grants from National Institute of Health and grants and personal fees from Metagenics and the California Walnut Commission. The other co-authors reported having no disclosures of interest.
Reviewed by Henry A. Solomon, MD, FACP, FACC Clinical Associate Professor, Weill Cornell Medical College and Dorothy Caputo, MA, BSN, RN, Nurse Planner