The authors of the study, published in the journal PLOS Medicine, said it was prompted in part by the fact that, globally, dietary risk factors cause an estimated 11 million deaths and the loss of 255 million years of life each year.

The study estimated how life expectancy is impacted by sustained changes in the intake of food such as "fruits, vegetables, whole grains, refined grains, nuts, legumes, fish, eggs, milk/dairy, red meat, processed meat, and sugar-sweetened beverages."

The study found that making a sustained change at age 20 from a "typical Western diet" to an optimized diet — which included a substantially higher intake of whole grains, legumes, fish and vegetables and a reduced intake of red and processed meats, sugar-sweetened beverages and refined grains — would increase life expectancy by more than a decade for women from the United States and by 13 years for men.

It also found that making a sustained change at age 20 from a typical Western diet to a feasibility approach diet, a midpoint between the typical Western diet and an optimized diet, would increase life expectancy by 6.2 years for women and 7.3 for men.

The study added that to have the maximum impact on life expectancy, the largest gains would be made by eating more legumes, whole grains and nuts and eating less red meat and processed meat.

The study found a positive impact not just for people changing their diet at 20 years of age but for all age groups, though it noted that "gains are predicted to be larger the earlier the dietary changes are initiated in life."

It found that changing from a typical Western diet to an optimized diet at age 60 would increase life expectancy by 8 years for women and 8.8 years for men, and that those making a sustained change at age 80 would gain about 3.4 years. 

The Centers for Disease Control and Prevention (CDC) 2020–2025 Dietary Guidelines for Americans also advise incorporating more fruits and vegetables as part of healthy dietary patterns.

A CDC study published last month found that only about 12 percent of U.S. adults consume 1 1/2 to 2 cups of fruit each day, which is the amount recommended by the agency's dietary guidelines. It added that only 10 percent of Americans eat the recommended intake of vegetables each day, which is around 2 to 3 cups.