A healthy diet in midlife could increase your chance of achieving an improved quality of life in later years, a Harvard study has found.

The research, unveiled on Tuesday at Nutrition 2024 event in Chicago, held by the American Society for Nutrition, reveals the close relationship between midlife diet and healthy ageing.

The study found that fewer than one in 10 people were able to live free of disease and maintain good physical, cognitive and mental health to age 70 and beyond.

The research, based on data from more than 100,000 people spanning 30 years, revealed that people who followed a healthy diet from their 40s onwards were 43 per cent to 84 per cent more likely to be well-functioning physically and mentally at age 70 compared with those who did not.

Anne-Julie Tessier, postdoctoral fellow at Harvard TH Chan School of Public Health in Boston, who conducted the study, said a diet high in fruit and vegetables can improve the way a person ages.

“People who adhered to healthy dietary patterns in midlife, especially those rich in fruit, vegetables, wholegrains and healthy fats, were significantly more likely to achieve healthy ageing,” she said.

“This suggests that what you eat in midlife can play a big role in how well you age.”

The researchers found that higher intakes of fruit, vegetables, wholegrains, unsaturated fats, nuts, legumes and low-fat dairy products were associated with greater odds of healthy ageing, while higher intakes of trans fat, sodium and meat were linked to lower odds.

Previous studies have shown that a healthy diet can help to ward off chronic diseases, however, the latest research focuses on the absence of disease at 70 and the ability to live independently and enjoy a good quality of life.

“Traditionally, research and derived dietary guidelines have focused on preventing chronic diseases like heart disease,” Ms Tessier said.

“Our study provides evidence for dietary recommendations to consider not only disease prevention but also promoting overall healthy ageing as a long-term goal.”

Researchers analysed data from more than 106,000 people going back to 1986.

Participants were at least 39 years old and free of chronic diseases at the start of the study and provided information about their diet via questionnaires every four years.

As of 2016, nearly half of the study participants had died and only 9.2 per cent survived to age 70 or older while maintaining freedom from chronic disease and experiencing good physical, cognitive and mental health.

The researchers compared rates of healthy ageing among people in the highest versus lowest adherence to each of eight healthy dietary patterns that have been defined by previous scientific studies, including a Mediterranean and a plant-based diet.

“A finding that stood out was the association between the 'planetary health diet' and healthy ageing,” Ms Tessier said.

“This diet is based on the EAT Lancet Commission’s report which emphasises fruit, vegetables, wholegrains, plant proteins and healthy fats from sustainable sources.

"The fact that it emerged as one of the leading dietary patterns associated with healthy ageing is particularly interesting because it supports that we can eat a diet that may benefit both our health and the planet.”

The ties between diet and healthy ageing remained strong even when the researchers accounted for physical activity and other factors that are known to affect health.

Given the study’s focus on dietary patterns in middle age, Ms Tessier believes future research could help to elucidate the potential impact of switching to a healthier dietary pattern later in life.