“All of the healthy diet protocols looked at in this study are based on whole, nutrient-dense foods, plant-biased but not exclusively plant-based, and contain mostly moderate amounts of lean animal protein,” says Dr Linia Patel, a researcher in the department of clinical sciences and community health at the Universita degli Studi di Milano in Italy and a spokeswoman for the British Dietetic Association (BDA). “Critically they also contain minimal ultra-processed foods and lower than average levels of salt and sugar.”

• The simple diet to join elite band of truly healthy over-70s

In 2016, three decades after the study began, those taking part were measured for markers of healthy ageing, defined as living to their 70th birthday without a chronic condition or impairment such as cancer, type 2 diabetes, stroke, multiple sclerosis and Parkinson’s disease. Typically, fewer than one in ten people reach this milestone in rude physical, mental or cognitive health. The results, published in Nature Medicine, found that 9,771 of the study participants, or 9.3 per cent, aged healthily by the time they turned 70. Unsurprisingly, given what we know from previous studies, those sticking to any one of the healthy diet patterns consumed relatively more fruits, vegetables, wholegrains, nuts and pulses and so fared much better than those with higher intakes of ultra-processed foods, salt and sugar, who had a 32 per cent lower chance of healthy ageing.

Beyond that the study did provide more detail about what we should be eating to stave off disease. Of the eight approaches assessed, the healthiest diet was the AHEI, which entails eating at least one serving of fish a week and at least five servings of vegetables, four of fruit, five to six of wholegrains and one of nuts or pulses every day. Those most closely matching the AHEI approach were found to be at an 86 per cent greater likelihood of healthy ageing, and at a 2.2 times greater chance of being healthy at 75 years compared with those with diets high in refined and processed foods. A general plant-based diet free of animal-based foods had the weakest association with healthy ageing, but was still better than diets high in salt, sugar and saturated fats.

Marta Guasch-Ferré, an adjunct associate professor of nutrition at Harvard and one of the authors, says midlifers certainly don’t need to be fully plant-based or vegetarian to become healthy agers. Lean animal protein — such as fish and poultry — and dairy were consumed by some, although not all, of the elite eaters. “It’s not just about living longer but also maintaining good health in the later stages of life,” she said. And the researcher stressed that there were positive elements of each of the healthy eating approaches. “Our findings also show that there is no one-size-fits-all diet,” says Anne-Julie Tessier, assistant professor in the department of nutrition at the University of Montreal. “Healthy diets can be adapted to fit individual needs and preferences.”

Patel says the study sends an important message to anyone inclined to follow the latest dietary trends. “These results highlight the fact that good general nutrition patterns, rather than a focus on individual superfoods or a restrictive approach, can help you not only to live longer but to live healthier too,” she says. “Ultimately, it shows that a well-balanced diet is one of the most powerful tools we have for healthy ageing.”

Here are the foods the study showed we should (and should not) be eating regularly to age well:

Eat legumes twice a week

GETTY IMAGES

Get at least five a day of fruit and veg

If you are not getting the five a day of fruit and veg recommended by the UK government — and according to the BDA most adults get only four daily portions — that is a starting point. But if you are, you can raise the bar even higher. Guidelines for the AHEI approach suggest pitching for five servings of vegetables a day with an extra focus on green leafy vegetables and less focus on potatoes and starchy veg. On top of that it suggests consuming four servings of fruit a day, “an amount that might help protect against cardiovascular disease and some cancers”, with berries, apples and pears all on the target menu. Fruit juice should be limited because it lacks the beneficial fibre found in the whole fruit.

Eat up to six servings of wholegrains a day

The five to six daily servings of fibre-rich wholegrains recommended in the AHEI diet sounds a lot. However, this can include: oats, which are particularly rich in beta-glucan, a soluble fibre that has been shown to lower blood cholesterol levels; quinoa, which is a source of quercetin and kaempferol, powerful antioxidants that have anti-inflammatory and antiviral properties; and rye, a good source of B vitamins and rich in lignans, a type of polyphenol compound that has antioxidant, immune-supporting benefits. Other wholegrains include brown and wild rice, barley, buckwheat and “ancient grains” such as freekeh. “As a rough guide, we should aim for at least a handful of wholegrain carbs at each main meal,” Patel says.

Consume a tablespoon of olive oil a day

All the healthy eating plans in the latest study favoured olive oil and plant oils over saturated animal fats. Another recent study, of more than 200,000 people in JAMA Internal Medicine, suggested that substituting less than a tablespoon of butter for equivalent calories from plant-based oils each day could lower cancer deaths and reduce early deaths by 17 per cent. Patel says that prioritising unsaturated fats such as plant oils can help to improve blood cholesterol levels and support a healthy heart. Olive oil’s particular benefits stem from the monounsaturated fatty acids, including oleic acid, it contains, which reduce inflammation in the body.

Eat pulses and legumes 2-3 times a week

One serving of protein and fibre-rich pulses or legumes — chickpeas, beans and lentils — a day produced the greatest health gains in the latest study. A previous study by Harvard scientists in the American Journal of Clinical Nutrition showed that adopting the PHDI diet — cutting down on meat and dairy in place of a diet including plenty of legumes and pulses — led to lower rates of premature death from heart disease, cancer and other diseases.

And Patel was an author of a paper in the European Journal of Clinical Nutrition that showed how eating just a 40g portion of dried pulses (about three tablespoons when cooked) a week reduced the risk of colon cancer by 21 per cent compared with those who ate no pulses. “Ideally we should eat beans, peas and lentils 2-3 times a week,” Patel says. “However, once a week produces big health gains so is better than none.”

Eat fatty fish at least once a week

The AHEI, Mediterranean and MIND diets recommend eating at least one serving of fish a week while the NHS says that most of us should be aiming for two portions of fish a week, at least one of which should be the fatty variety. Oily fish such as mackerel and sardines provide vitamins A and D and are a source of the long-chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid that have anti-inflammatory properties and may help cognitive health. “Essential fatty acids such as omega-3s cannot be made in the body and must be provided in the diet,” Patel says. “Oily fish is a very good source, although you can also get these in walnuts and pumpkin seeds.”

Cut down on ultra-processed foods and avoid processed meat

In the new study, participants with a higher intake of ultra-processed foods, especially salty, high-fat foods and sugary and diet drinks, had a 32 per cent lower chance of healthy ageing. Cutting down on UPFs including savoury snacks, processed meats, ready meals, and sugar-sweetened and artificially sweetened beverages was associated with reduced incidence of type 2 diabetes in a study by University College London last year. And a team at the University of Bristol previously suggested high intakes of UPFs are linked to a higher risk of some cancers.

“A lot of UPFs do contain high amounts of saturated fat, linked to raised cholesterol levels, sugar and salt, and are also low in fibre, all of which can be problematic in a diet long term,” Patel says. “Some additives in UPFs might be linked to changes in our gut microbiome which also influence health, so it is definitely worth cutting down if you eat a lot of them.” Processed meats — sausages, bacon, ready-made pies — should be avoided as much as possible as the NHS says studies have shown high intakes are linked to bowel cancer.