Your ‘true’ biological age – and how to reverse it

1. Switch to a plant-based diet 75 per cent of the time

Protein has an ageing effect due to the impact IGF-1, a chemical involved in growth, has on the body. In a study of 3,000 Americans, at the University of Sydney, Levine and Dr Valter Longo, found that a high protein diet, with 20 per cent of calorie intake from protein, was associated with a 74 per cent increased risk of dying early compared to those in the low protein group of less than 10 per cent. 

However, these differences disappeared when the protein was chiefly from vegetarian sources and those over 65 should be wary of cutting down too much. “It is a little bit nuanced,” says Levine. “Protein is not a problem for people who are young or middle-aged, because their bodies are still naturally generating enough growth hormone. But as people grow older, this is a time where I would say eating a little more protein, whether that’s healthy animal products or vegetarian forms might be beneficial, especially for people who might be losing too much muscle mass.”

2. Fast three times a year

Research by Levine, in collaboration with Longo, found that three cycles of fasting, eating only 4,500 calories over five days, reduced biological age, with subjects appearing 2.5 years younger. Fasted subjects also showed “more youthful immune profiles” following multiple cycles of fasting.  

“It’s what we call a ‘hormetic’ effect, where it’s this mild stressor, and your body responds to that and improves,” says Levine. “Like exercise, fasting seems to prime the body for repair and maintenance.” 

When the scientists looked at the potential long-term impact of fast mimicking diets (FMD) the data suggests that 20 years of FMD could buy individuals an extra five years of life expectancy, as well as reducing heart disease risk by 50 per cent, cancer risk by 30 per cent and diabetes by 75 per cent.  

FMD is typically done once a month or a few times a year. In FMD each cycle consists of 4,500 calories, the first day is 1,000 calories; day 2 is reduced to 700 calories.  

Focus on vegetable soups and bean soups and cut out meat and reduce your protein intake to 10 per cent. Other fasting methods like time-restricted eating also work to reduce biological age.

3. Do HIIT, high-intensity interval training

The short, sharp shocks of HIIT training are best for turning back the clock, says Levine. A 2017 study at the Mayo Clinic showed that three months of HIIT training was enough to substantially improve fitness and insulin sensitivity. “You do five or seven minutes, push, and then you get one or two minutes recovery,” says Levine.  

The key is to go all out, aiming for 90 per cent effort. Again, it comes down to “hormesis”, where the body undergoes a shock, then adapts and improves. “Muscle fibres grow back thicker and denser, mitochondria becomes more efficient at generating usable energy, and processes like inflammation are turned down,” explains Levine. Exercise also stimulates GPLD1, a protein-coding gene that improves cognitive performance.

4. Good quality sleep

Research scientists at Boston and Harvard University used MRI scans to show that cerebral fluid (CSF) washes over our brain tissue in waves at night washing out dead cells. Scientists think this might have implications for Alzheimer’s, which is associated with the build-up of “amyloid beta plaques”. 

Restless sleep might be due to the natural decline of NAD (nicotinamide adenine dinucleotide), a protein that protects against oxidative stress and helps brain cells age well and also appears to be crucial to our circadian clock.  

The best ways to increase NAD appears to be through fasting and exercise, though supplements are also available. Research shows the sleep sweet spot is around seven hours on average. Less than five hours reduces lifespan, as does more than eight, with 10 being the highest risk.


True Age, Cutting-Edge Research To Help Turn Back The Clock, by Dr Morgan Levine, Yellow Kite, £16.99, is out on May 3

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