A striking example comes from Britain’s wartime past. During the Second World War, food rationing was introduced to ensure fair distribution of limited supplies. Sugar was tightly controlled, with adults allowed roughly 227 grams a week. Babies and toddlers under two, however, were given none at all.

When rationing ended in 1953, sugar consumption soared almost overnight. At the time, no one imagined this abrupt shift would later become a natural experiment for scientists. Yet decades on, researchers have been able to trace the long-term health effects of early-life sugar exposure by studying people born during and just after rationing.

A major 2025 study published in the BBC examined medical records of more than 63,000 individuals born in the UK in the early 1950s. Those exposed to lower sugar intake before birth and in their first 1,000 days of life were significantly less likely to develop heart disease, heart failure or stroke in adulthood. The findings, reported by the BBC, provide some of the clearest evidence yet that nutrition in early life can shape health decades later.

Sugar is not unique in this respect. While excessive sugar intake is harmful at any age, other nutrients play different roles depending on life stage. For example, the high-fat content of whole milk is essential for babies and young children, but far less appropriate for adults.

Childhood: building the body and brain

“In childhood, food is literally constructing the brain and body,” explains Federica Amati, a nutritional scientist at Imperial College London. Children have high energy demands and require a dense supply of nutrients to support growth, immunity and cognitive development.

Iron, iodine, vitamins and healthy fats are particularly important, alongside a diet rich in fruit, vegetables, wholegrains, beans and lentils. Ultra-processed foods, by contrast, offer little nutritional value at a stage when every calorie counts.

Bone development is another priority. Most bone mass is laid down during childhood and adolescence, making calcium and vitamin D essential. Dairy products, fortified plant-based drinks, tofu, fish and eggs all contribute, while sunlight helps the body produce vitamin D naturally.

Long-term studies show these early choices matter. Children who met several dietary recommendations by the age of seven were found to have healthier cardiovascular markers as young adults, reinforcing the idea that good nutrition early on pays off later.

Teens and early adulthood: laying foundations for the future

Adolescence and the twenties are often overlooked in discussions about long-term health, yet they represent a critical window. Growth may slow, but bones and muscles are still developing, and lifelong habits are being formed.

Calcium, iron, protein and B vitamins are especially important during this stage, particularly for those who menstruate. Amati recommends a largely plant-based diet with sufficient protein at every meal, whether from animal or plant sources.

There is also growing evidence linking teenage diets to mental health. Diets high in ultra-processed foods are associated with higher rates of anxiety and depression, while Mediterranean-style diets appear protective. Rich in vegetables, legumes, nuts and olive oil, this pattern has also been linked to better fertility outcomes for both men and women.

Midlife: protecting heart, muscle and bone

By middle age, the focus shifts towards preventing decline. For women, the menopausal transition brings increased risks of osteoporosis, heart disease and weight gain, partly due to falling oestrogen levels.

“Around the forties and fifties, heart health and muscle preservation become central concerns,” Amati explains. Omega-3 fats from oily fish help reduce cardiovascular risk, while higher protein intake can slow muscle loss.

Large population studies suggest that diets rich in fruits, vegetables, wholegrains, nuts and unsaturated fats are strongly linked to healthy ageing, defined not just by longevity but by maintaining physical, cognitive and mental wellbeing.

Later life: fewer calories, more nutrients

In older age, energy needs fall, but nutritional needs remain high. Calcium and vitamin D become crucial for preventing fractures, while protein is essential to counter sarcopenia, the age-related loss of muscle mass.

Gut health also takes on greater importance. As we age, the diversity of our gut microbiome tends to decline, which has been linked to conditions such as heart disease and dementia. Interestingly, centenarians often have unusually diverse gut bacteria.

“People who live to 100 seem to defy many aspects of ageing,” says Mary Ni Lochlainn of King’s College London. Diets high in fibre and plant compounds called polyphenols appear to support beneficial bacteria linked to better health.

Some supplements may also help in later life. Research suggests that prebiotics and vitamin D supplements can offer cognitive and physical benefits, particularly for older adults with limited dietary intake.

The bigger picture

Across the lifespan, one message stands out: small, consistent dietary choices matter, and their impact depends heavily on timing. From reduced sugar exposure in infancy to protein intake in old age, nutrition shapes how we age in ways that are only now becoming clear.

As BBC science coverage has repeatedly highlighted, ageing well is not about drastic interventions but about aligning what we eat with what our bodies need at each stage of life.