One of the most successful anti‑ageing strategies ever discovered is caloric restriction. 

It requires a permanent cut in energy intake of up to 60 per cent. 

In every experimental animal that has been put through this, from fruit flies to primates, it extends lifespan and health span, which is the number of disease-free years at the end of life. 

The strategy works because it switches on an evolutionary adaptation to starvation, which prioritises repair and survival pathways overgrowth and reproduction. 

Calorie-restricted animals tend to be leaner, fitter, metabolically healthier and mentally sharper than those that eat at will. They also have a stronger immune response. Unfortunately, caloric restriction is extremely hard to maintain voluntarily. But there are ways to mimic it without going on a permanent starvation diet. 

The key is to deactivate a nutrient-sensing pathway inside cells called mTOR. 

When calories are scarce, it switches off, initiating the metabolic cascade that transitions your system into famine mode. 

There are various regimes including the 16:8 diet, which involves completely eschewing calories for 16 hours and only eating in an 8-hour window. Even done once a week, this is an effective way of slowing ageing and strengthening the immune system. 

If a fasting diet isn’t for you, simply keeping your weight down can have immune-boosting effects. 

According to Bonnie Blomberg at the University of Miami in Florida, being obese suppresses the immune system to a similar extent as being immunosenescence, i.e., anyone that has an immune dysfunction that occurs with age.

Ageing is associated with a decline in the function of the immune system’s B-cells and low production of antibodies in response to vaccines, and so is being obese. “Adipose tissue negatively impacts the antibody response,” says Blomberg. “So obesity is associated with poor vaccine response, even in people who are young.”