When it comes to how we live our lives, most people would say everything is good in moderation. In many cases that would be good advice; drinking alcohol, working from home, spending time in front of the TV should all be done in moderation. But according to a new study, published in PLOS ONE, it might not apply to the way we eat.

Researchers from the University of Texas Health Science Center in Houston (UTHealth) and the Friedman School of Nutrition Science and Policy at Tufts University found mixing up the foods we eat could result in having a lower-quality diet and possibly even lead to worse metabolic health.

"'Eat everything in moderation' has been a long-standing dietary recommendation, but without much empiric supporting evidence in populations," said first author Dr. Marcia C. de Oliveira Otto, assistant professor in the Department of Epidemiology, Human Genetics, and Environmental Sciences at UTHealth School of Public Health, in a press release. "We wanted to characterize new metrics of diet diversity and evaluate their association with metabolic health."

Metabolic health is a catch-all term for the proper functioning of the organs and other body processes that help our metabolism run at peak efficiency. With proper metabolic function, we keep our weight, blood pressure, and blood sugar levels in line. On the other hand, people with poor metabolic health often suffer from metabolic syndrome, a cluster of health conditions, such as high blood pressure and "bad" cholesterol and excess abdominal fat, that increase risk of type 2 diabetes and heart disease.

Researchers used data from the Multi-Ethnic Study of Atherosclerosis, which sought to analyze dietary diversity among 6,814 U.S. participants who were either white, black, Hispanic-American, or Chinese-American. The study counted the number of different foods participants ate each week, the distribution of calories between the foods they consumed, and differences in the foods’ nutritional content that was relevant to metabolic health — like fiber, sodium, or trans-fat content.

Waist circumference is an important indicator of health because the fat surrounding the abdominal organs is metabolically active, meaning that releases fatty acids, inflammatory agents, and hormones that affect cholesterol, blood glucose, and blood pressure. With more abdominal fat comes a higher risk of metabolic abnormalities, and thus a higher risk of chronic disease. For the study, researchers looked at changes in waist circumference five years after it began. Then, after 10 years, they followed up again to determine how many people developed type 2 diabetes.

When they looked at the number of different foods participants ate per week as well as the distribution of calories spread across those foods, the researchers found that even with a diverse diet, people were still at risk of growing a larger waistline or developing diabetes. Participants with the most diverse diet were also found to have the most central weight gain, with a 120 percent larger waist circumference than participants with the least diverse diet.

"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," Otto said. "This may help explain the relationship between greater food dissimilarity and increased waist circumference."

According to Dr. Dariush Mozaffarian, senior author and dean of the Friedman School of Nutrition Science and Policy at Tufts University in Boston, the Americans with the healthiest diets were those who were eating a "relatively small range of healthy foods. These results suggest that in modern diets, eating 'everything in moderation' is actually worse than eating a smaller number of healthy foods."

Source: Otto, M, et al. Everything in Moderation - Dietary Diversity and Quality, Central Obesity and Risk of Diabetes. PLOS One . 2015.