The US-based research team analysed the diets of nearly 7,000 people to test how diet diversity was associated with change in waist circumference five years after the beginning of the study and with onset of Type 2 diabetes 10 years later.
Writing in PLoS One, the researchers measured diet diversity through different measures, including the total count (number of different foods eaten in a week), evenness (the distribution of calories across different foods consumed), and dissimilarity (the differences in food attributes relevant to metabolic health, such as fibre, sodium or trans-fat content).
"'Eat everything in moderation' has been a long-standing dietary recommendation, but without much empiric supporting evidence in populations. We wanted to characterize new metrics of diet diversity and evaluate their association with metabolic health," said first author, Dr Marcia C. de Oliveira Otto, at The University of Texas Health Science Center at Houston (UTHealth).
They found no association for both food count and evenness for waist circumference or incidence of diabetes – suggesting that more diversity in the diet was not linked to better outcomes.
However, Otto and her colleagues found that participants who had the greatest food dissimilarity actually experienced more central weight gain, with a 120% greater increase in waist circumference than participants with the lowest food dissimilarity.
"An unexpected finding was that participants with greater diversity in their diets, as measured by dissimilarity, actually had worse diet quality. They were eating less healthy foods, such as fruits and vegetables, and more unhealthy foods, such as processed meats, desserts and soda," said Otto. "This may help explain the relationship between greater food dissimilarity and increased waist circumference."
"These results suggest that in modern diets, eating 'everything in moderation' is actually worse than eating a smaller number of healthy foods,” commented senior author Dr Dariush Mozaffarian from Friedman School of Nutrition Science and Policy at Tufts University.
The research team from UTHealth and Tufts analysed data from 6,814 participants in the Multi-Ethnic Study of Atherosclerosis, testing the association between diet diversity and changes in waist circumference five years after the beginning of the study and with onset of Type 2 diabetes (T2D) 10 years later.
“In multivariate models, neither count nor evenness was associated with change in waist circumference (WC) or incident T2D,” wrote the team. “Greater food dissimilarity was associated with higher gain in WC (p-trend<0.01), with 120% higher gain in participants in the highest quintile of dissimilarity scores.”
To compare with the results seen for diet diversity, the researchers also examined how diet quality relates to metabolic health.
Diet quality was measured using established scores such as the Dietary Approaches to Stop Hypertension (DASH) score and the Alternative Healthy Eating Index (AHEI) score. At five years, diet quality was not associated with change in waist circumference.
At ten years, higher diet quality was associated with about a 25% lower risk of developing Type 2 diabetes, they said.
“Our findings provide little evidence for benefits of dietary diversity for either waist circumference or T2D,” the team concluded – noting that greater dissimilarity among foods was actually positively associated with increase in waist circumference.
“Our results challenge the notion that “eating everything in moderation” leads to greater diet quality or better metabolic health,” they said – adding that the research supports the importance of diet quality, independent of diversity, and highlights the need for greater investigation of relationships between diet diversity and metabolic health.
Source: PLoS One
Published online ahead of print, doi: 10.1371/journal.pone.0141341
“Everything in Moderation - Dietary Diversity and Quality, Central Obesity and Risk of Diabetes”
Authors: Marcia C. de Oliveira Otto, et al