Switching to a healthy diet could add 10 years to your life. 3 foods seemed to make the biggest difference in a study.

• Changing an unhealthy diet to a healthy diet in middle age could add 10 years to a person's life. 
• A study found that eating lots of whole grains, nuts, and fruits could make the biggest difference. 
• The bigger the change to the diet, the bigger the expected life expectancy gains in the study.

Switching from an unhealthy to a healthy diet in middle age could add almost a decade to a person's life, a new study suggests.

The study, published Monday in Nature Food, was based on a model used to estimate how lifestyle changes could affect a person's life expectancy, and used data on 467,354 participants from the UK Biobank, a large-scale biomedical database and research resource containing genetic and health information on half a million UK participants.

The model found that people in their 40s who switched their unhealthy diet to a longevity-associated diet could add around 10 years to their life expectancy. The change was associated with an extra 10.8 years for women and 10.4 years for men.

Going from eating an average diet, rather than an explicitly unhealthy one, to the longevity-associated diet was meanwhile linked to a life expectancy gain of 3.1 years for women in their 40s, increasing slightly to 3.4 years for men. Making the same dietary changes in their 70s was associated with a life expectancy gain of around five years.

"Gains in life expectancy are lower the longer the delay in the initiation of dietary improvements, but even for those initiating dietary change at age 70 years, the gain in life expectancy is about half of that achieved by 40-year-old adults," the authors wrote.

But overall, they found that the bigger the changes towards a healthy diet, the bigger the expected gains in life expectancy were.

Whole grains, nuts, and fruit were associated with the biggest life expectancy gains

The researchers at the University of Bergen, Norway, and the University of Glasgow, Scotland, found that whole grains, nuts, and fruits appeared to make the biggest positive difference to life expectancy. Those that were most closely linked to mortality were sugar-sweetened beverages and processed meat, the study said.

According to the researchers' analysis, a longevity-associated diet consisted of a high intake of milk and dairy, vegetables, nuts, and legumes, and a moderate intake of whole grains, fruit, fish, and white meat.

It also included a relatively low intake of eggs, red meat, and sugar-sweetened beverages, and a low intake of refined grains and processed meat.

This has parallels with the Mediterranean diet, which is widely considered one of the healthiest ways to eat and emphasizes whole grains, lean proteins, fruits and vegetables, and healthy fats, while limiting processed foods, as well as sugary and fried foods.

The unhealthy dietary pattern, which was most closely associated with dying sooner, contained no or limited amounts of whole grains, vegetables, fruits, nuts, legumes, fish, milk and dairy, and white meat and substantial amounts of processed meat, eggs, refined grains, and sugar-sweetened beverages.

The authors acknowledged that their study showed correlation, not causation, between a healthy diet and longer life expectancy. However, they adjusted their model to try to prevent factors such as smoking and socioeconomic status from skewing the results.

They also did not consider the possibility of dietary patterns fluctuating over time, they said.

An additional limitation was that the UK Biobank does not measure participants' consumption of rice, which is particularly important for many migrant groups, the study said.

Professor Gunter Kunhle, a nutritional scientist at the University of Reading, UK, who was not involved in the research, told Business Insider: "The findings are in keeping with the known evidence about the types of diets that lead to longer, healthier lives in individuals.

"It should also be noted that a modeled population is very different from a real one. While it's technically possible, and also sensible, for a 40-year-old to switch from decades of unhealthy diet to decades of sensible, balanced nutrition, it can be hard to do. This paper provides additional evidence of why it's good for us all to promote a healthy, balanced diet at every stage of life."