For decades nutrition experts have encouraged Americans to eat a variety of foods to ensure that they consume a nutritionally adequate diet. But this week a panel of experts said that longstanding recommendation might be outdated.

The advice to consume a variety of foods has long been included in the federal government’s Dietary Guidelines for Americans. It is largely based on old studies of low-income populations that found that consuming a broad range of foods helped prevent nutritional deficiencies.

But in today’s environment, where food is plentiful and malnourishment less prevalent, that advice could backfire, said Marcia Otto, an assistant professor in the department of epidemiology, human genetics and environmental sciences at UTHealth School of Public Health in Houston.

Dr. Otto was part of a panel of experts with the American Heart Association that examined the latest evidence behind the recommendation. The panel released a scientific report on Thursday in the journal Circulation that found that in some studies, people whose diets contained the greatest variety of foods tended to eat many nutritious foods, like fish, fruits and vegetables, but also many junk foods, such as sugary snacks and beverages, refined grains and other processed foods.