‘Everything in Moderation’ Is Bad Diet Advice

A study showed that eating a wide variety of foods was associated with weight gain. Dwight Eschliman/Getty Images

Along with "eat less and move more," the next most common diet advice might be "everything in moderation." When you deprive yourself of some food or the other, the thinking goes, it becomes an unnecessary craving. And if you just have a little now and again, it can't do too much harm. Findings from a recent study published in PLOS ONE fly in the face of that philosophy, saying that “diet diversity” (the number of different foods a person eats in a given period of time) may actually make you fatter. 

Researchers at The University of Texas Health Science Center at Houston (UTHealth) and the Friedman School of Nutrition Science and Policy at Tufts University analyzed data from more than 6,000 people who participated in the long-running Multi-Ethnic Study of Atherosclerosis, which collected diet and other information from a range of whites, blacks, Chinese-Americans and Hispanic-Americans in an effort to identify risk factors for heart disease. They looked specifically at this info reported by participants and measured several nutrition diversity-related categories:

  • The number of different foods they consumed in a given week (diet diversity)
  • How evenly calories were distributed across foods (Big Mac versus green salad)
  • How similar or dissimilar the foods were from each other in terms of how they affect metabolic health, like sodium or fiber content

“In previous large studies what they did was ask people how many different foods they ate in a week,” explains Marcia C. de Oliveira Otto, Ph.D., assistant professor at UTHealth. “That number alone was not catching a lot about the differences in the foods." 

Researchers for Otto's study developed an index defining attributes that foods have related to healthfulness. So, a sweet potato is going to rate a lot better than a candy bar, giving a more accurate picture as to the overall quality of a person's diet.

After analyzing the dietary reports, the researchers compared the information with the waist circumferences of participants after five years and their Type 2 diabetes risk after 10. They found that the sheer number of different foods and caloric evenness didn't positively affect diabetes risk or waist circumference. In other words, eating a wide range of foods isn't going to earn you any health-related awards because the range often includes a lot of poor nutritional choices.

In fact, after five years, the people who reported higher levels of dissimilarity in their food choices actually experienced about a 120 percent greater increase in waist circumference than those participants who ate the same types of stuff all the time. This was a surprise to the researchers.

“We found that people with more dissimilarity were eating less of the healthy and more of the unhealthy,” says Otto. “We suspect that the benefits from eating healthy foods was actually outweighed by the potential harm of eating unhealthy foods. So, basically eating a little bit of everything was not leading to health benefits as we used to think.”

Of course, this outcome is assuming that the more limited selection of foods the person eats is all healthy as opposed to, say, a limited but fattening diet of burgers, fries and ice cream.

“The ‘little bit of everything' notion is actually giving people permission to eat more of the unhealthy foods,” Otto says. “This notion is playing a role in populational health.”

More to Explore