‘Nutrition is one of the hardest sciences to do well,” says Graham Lawton, a science writer whose first book, This Book Could Save Your Life, aimed to debunk a number of contemporary health fads. “Humans are terrible research subjects,” he says. “Recording what they actually eat is virtually impossible, they either forget or they lie.” And, he says, “everybody’s different. Everyone has a different gut microbiome and metabolism.”

While Lawton is clear that it’s almost impossible to pull out any kind of generalisation, there is some consensus over the sorts of food we might want to prioritise at various life stages. Generally speaking, ultra-processed foods are always best avoided regardless of age, due to the high sugar, salt and artificial trans fats that characterise them (also called “partially hydrogenated oils”, artificial trans fats can be found in hard margarine, fast food and commercially produced baked goods, and have been so closely linked to heart disease that they have been banned in Denmark, Switzerland, Austria and certain US states). As for everything else? “It’s about moderate doses,” says Lawton. Here’s what to eat by age.

0-two years old

What to eat: leafy greens, eggs and full-fat dairy

The NHS recommends that parents start weaning their children at around six months old. “This is because there’s not enough iron in breast milk, so mum and the baby can become anaemic,” explains Sophie Medlin, dietitian and London Chair of the British Dietetic Association. Eggs are a powerful choice even at this age, though the NHS says eggs without the Red Lion label are not suitable to be eaten raw (for example in homemade mayonnaise). and “adding iron-rich vegetables to meals such as spinach and broccoli, which are easy to puree, is great,” says Medlin.

Rachel Ward is a GP in Oxfordshire. She recommends parents use full-fat milk, full-fat yoghurts and full-fat cheese for the under twos, “because of their fast growth rate. They are using up a lot of energy and they’ll need it,” she says. Ward stresses the importance of introducing children to a variety of food at the earliest opportunity. “We know the first time they try fruit and vegetables, they won’t like them, but it is important that you keep going because that’s the building blocks of a broad and balanced diet.”

Two years old to teens

What to eat: seeds, tofu and semi-skimmed milk

“This period is really rapid for bone growth,” says Medlin. “So it’s about making sure they eat lots of calcium-rich food. Dairy is optimal.” By now, Ward suggests they’re switched to semi-skimmed milk and lower fat dairy options – for example, creme fraiche over cream – as part of forming healthy habits. “Iron also remains important, so keep pushing a range of vegetables,” she says. For calcium-rich plant-based alternatives, “seeds and tofu are excellent,” says Medlin, with sunflower, chia, poppy and sesame being some of the most powerful.

Teens and young adults

What to eat: pulses, lean meats, dried fruits, and flavours from around the world (ideally cooked as a family)

“The diet should be balanced and nutrient rich,” says Ward. “Fruit and veg, lean meat, and pulses. Parents should also try to build up an array of foods using new flavours and ingredients from different countries.” For maximum impact, make cooking a team effort. “Encourage the kids to take ownership of their diet so they have a good repertoire of recipes,” she says. “It’s not going to be long before they have left home and you want them to have the skills to eat healthily.” Once again, iIron is important, especially for girls experiencing the onset of menstruation: eggs, spinach and dried fruits are good sources. What about teenage skin? “That’s hormonal, there’s not a lot you can do about that through diet,” says Medlin.

20s

What to eat: foods rich in B vitamins

“At this phase in your life, health is on your side, and you can feel a little bit invincible,” reflects Ward. “But it’s still important to look at what you’re putting into your body, and understanding it has consequences. Something we see in this age group is alcohol excess, which can be detrimental if people get into the habit of drinking without food.” Medlin says the lifestyle changes in our 20s – some of them being alcohol, caffeine and stress – are a “perfect storm” for B12 deficiencies, especially as plant-based diets take off. “Foods rich in B vitamins are animal products like meat, fish, dairy and eggs. But iIf you’re vegan, you can use nutritional yeast to add extra B12 to your diet, andfocus on those green leafy vegetables.”

30s

What to eat: whole grains

The likes of pearl barley, oats and brown rice have a number of benefits for people in their 30s. Firstly, around this age, fertility may be on the agenda, so women trying to conceive could benefit from dialling up their consumption of folate to reduce the risk of neural tube defects like spina bifida. Good sources of folate include dark leafy greens and whole grains.

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Men could also benefit from keeping an eye on their B vitamins – again, whole grains are a good source, and they also promote feeling fuller for longer, which can help maintain a healthy weight. “A lot of people get to their 30s and suddenly their bowels don’t like certain foods, so gut health becomes more important. For that, you’d want to be focusing on high-fibre food,” says Medlin. And what’s a good source of fibre? Whole grains.

40s

What to eat: occasionally, nothing

“As we move into ageing processes, we need antioxidants to protect our skin and body,” says Medlin. Antioxidants work by neutralising unstable atoms in the body called free radicals. Free radicals cause cell damage and occur in the body through ageing and environment (for example, due to pollution and stress). You can find antioxidants in brightly coloured fruit and veg so it’s important to eat them, not take them in a pill or applied in a cream. “They don’t work unless eaten, for reasons that aren’t well understood,” says Lawton. “One theory is that they work by hormesis.” This is a biological process where a small amount of something harmful has beneficial effects. “So the antioxidant plants are mildly poisonous in order to keep insects off, and our body reacts to this insult by ramping up its protective mechanisms.”

If eating to slow ageing is your aim, Lawton only has one recommendation:s fasting. “There’s something called autophagy: if you deprive your body of nutrients for an extended period of time, your body has to find alternative sources of energy. So it finds loads of gubbins in your cells – bits of protein, old organelles, the cellular damage – and it burns them. It’s like cleaning out loads of old crap from inside you.” Fasting is associated with better metabolic health, and in animal experiments “has been tried on every conceivable animal from insects through to macaques, extending their lifespans by up to 50%”.

50s

What to eat: more olive oil, less butter

“In our 50s we want to be focusing on weight management, as well as diabetes and heart disease prevention,” says Medlin. “So it might be the time to start switching saturated fat for unsaturated fats.” But what does this mean? There are different types of fat in the food we eat, and saturated fats are the ones linked to high cholesterol. Many animal foods are high in saturated fats – butter, meat, cheese. “A good rule of thumb is that saturated fats tend to come from animals and are solid at room temperature,” says Lawton, “while unsaturated fats tend to derive from plants, and are liquid at room temperature.” Olive oil is a common unsaturated vegetable fat.

“There’s not been a lot of clarity on saturated fats,” reflects Lawton. “They were demonised based on less than rigorous research on the Mediterranean diet. That research was done in Greece at a time when people were fasting for religious reasons, so they were eating mostly fish and vegetables and olive oil. But they usually eat quite a lot of lamb, which is high in saturated fat. More recently, there’s been a saturated fats renaissance, particularly with butter.” But according to Lawton the bottom line is: “saturated fats are a perfectly healthy and essential part of a balanced diet, but we eat too many of them. And if you do eat too many of them, they are linked with obesity and heart disease.”

60s

What to eat: plenty of protein

Protein is the food group du jour, promising muscle gain to exercise enthusiasts and weight loss to dieters who are drawn to its ability to make people feel fuller for longer (and therefore consume fewer calories). “However, there are lots of major nuances to this,” warns Lawton, noting that in general the under-65s “eat too much protein in the west anyway”. But he says, protein could be beneficial for the over-65s in the battle against sarcopenia, which is muscle wastage.

70s onwards

What to eat: a fully balanced plate of food, with someone else

“Around this age, we tend to see people’s eating habits change. Appetite tends to decrease, especially when people retire and may be less active,” says Ward. “So if you are not eating as much, you need to be conscious that meals include all your nutrients.” Ward says that it’s not uncommon for older people to lack motivation to cook, especially if they’re on their own or have mobility issues. “I would highly recommend batch cooking when you’re up to it,” she says. “Or to use eating as an opportunity to socialise. Spending time with other people and eating together is great for many aspects of health.”

Life’s essentials: what to eat at any age

Lots of fruits and vegetables
There has been a debate over whether five-a-day is trulyenough to meet all our nutritional needs, but given most British adults only eat four portions and children only three, five seems like a worthy goal. Fruit and veg are nimble agents of nutrition, with many straddling essential groups – chickpeas are protein and vegetable, sweet potato is a carb and one of your five a day – so eating plenty of them is key. The trick is mixing it up, and giving your body a variety. A popular rule of thumb is to “eat the rainbow”. (However, there’s no evidence that eating a balance of colours leads to a balance in nutritional content.)

Omega-3
“All children have the potential to be academic,” notes Medlin. “So make sure they’re getting plenty of omega-3, whether that is from oily fish or a supplement.” Research suggests that fish oil could have a role in brain and eye development, and even in school performance, though consistent conclusions are lacking. There’s also been a number of studies that suggest eating fish could reduce inflammation and help with joint pain in our later years – though it’s once again inconclusive. Nonetheless, fish as a choice of protein is solid. The NHS recommends two portions a week. White-fleshed fish is among the leanest proteins and oily fish is high in omega-3 which can also help to keep your heart healthy.

Calcium
We know that calcium is crucial for growing children but we also need a good amount from 30 onwards. “After 30, each day that we don’t get enough calcium in our diet, our body leaches it from our bones,” says Medlin. “By the time we get to 60, quite a lot of the calcium from our bones will have gone.” Moreover, Ward says menopausal women should be mindful about calcium intake to prevent osteoporosis. NHS Scotland recommends two to three servings of dairy a day, so one glass of milk, a matchbox size piece of cheese and a yoghurt. For plant-based alternatives, trusty spinach and other leafy greens can help.