Most healthy eating advice focuses on eating a variety of foods to ensure you’re sampling from a range of different food groups. That way, health experts say, you’re more likely to get everything that your body needs.
But in the latest review of the topic, scientists found that having a diverse diet may not necessarily lead to better health.
In a statement published in the journal Circulation, the American Heart Association (AHA) reviewed the available studies and reported that there is little scientific support for the idea that a varied diet leads to good health outcomes – especially when it comes to lowering risk of chronic conditions like obesity, heart disease and diabetes.
In fact, more diverse diets, according to some of the latest studies the AHA committee reviewed, were linked to worse outcomes on these measures.
That’s because existing studies defined diversity in different ways, the scientists found, and also because people interpreted the need to eat a variety of foods in different ways.
That’s not entirely surprising, says the statement’s lead author, Marcia de Oliveira Otto, assistant professor of epidemiology, human genetics and environmental sciences at UT Health School of Public Health in Houston. To measure variety, most of the studies asked people about the number of different foods they ate – from snacks to meals to fresh produce.
And it turns out that people eating a wider range of foods also tended to eat more unhealthy foods, including processed snacks, cakes and sweets, compared to people like vegans who stick to fruits and vegetables and may not have as a high a count of different types of foods.
To determine whether a diet was diverse, the researchers in these previous studies also looked at the evenness of the diet, which measured which types of foods that provided the most energy or calories, and the dissimilarity of the diet, which measured specific features of different foods, such as the amount of fibre or how processed the food was.
Using these different definitions of diversity, the studies did not find an overall benefit in so-called diverse diets for health outcomes like heart disease and obesity.
When the studies focused on the quality of the diet, however, such as whether it contained mostly healthy fats, plenty of fruits and vegetables and limited amounts of red meat and dairy, they found that these diets were indeed associated with lower risk of chronic diseases.
“The world is changing, and the food environment is changing,” says Otto. A “diverse” diet means something different today, compared to when the advice to eat a variety of foods was first recommended in the early 19th century.
Back then, the health concerns cantered around malnutrition and people not receiving adequate amounts of nutrients and vitamins, so the recommendation to eat a variety of foods made sense to give people the best chance of getting their nutritional needs from everyday meals.
“Nowadays, we have shifted from the context of under-nutrition to over-nutrition, especially in countries like the U.S. and middle-income countries,” she says. “And now we are concerned about chronic diseases like heart disease, obesity and type 2 diabetes.”
That doesn’t mean that eating a variety of foods isn’t good for you; it’s just that people are interpreting the word ‘variety’ to include all kinds of foods, some of which may not necessarily be healthy.
A diverse diet, in other words, does not mean one that includes a range of unhealthy and healthy foods, since it’s possible that the unhealthy effects of the poor quality foods might outweigh the benefits of the healthy foods.
What might be more helpful, especially in today’s food environment with so many choices in what we eat, says Otto, may be focusing on the quality of the diet rather than its type.
That means advising people to eat as many plant-based foods, fruits, vegetables, vegetable oils and lean meats as possible, and cutting back on red meats and sugared foods. “We need to rediscover what diversity in diet means,” says Otto.