Three years ago this month, Dr Michael Mosley demonstrated ‘the power of intermittent fasting’ on the BBC programme Horizon. He based his argument for this regime on evidence that had been mounting for some time that calorie restriction can prolong life.
However, many scientists challenge these assumptions, partly because of a lack of consistency between the various studies on monkeys, mice, rats, and even fruit flies. A review published in 2014 recognised that calorie restriction diets might be inadvertently correcting pre-existing imbalances in nutritional intake in the laboratory animals.
A team of researcher in Sydney took a different approach. They already knew that individuals who were deficient in certain growth factors did not suffer from cancer or diabetes, both of which are associated with the ageing process. They also knew that production of these cellular growth factors required particular amino acids. As amino acids are the building blocks of protein, it made sense to explore the effects of differing amounts of protein in the human diet. They analysed the proportion of protein in people’s diets, drawing on an existing national USA dataset. They also had access to health and mortality information about the people in their sample.
The Sydney team discovered something quite remarkable. Among the age group 50-65, high animal (not plant) protein intake was associated with shorter lives. This high protein group were almost four times more likely to die from cancer, when compared with the low protein group.
For those aged 66 plus, however, the tables turned. For this older group, longevity was associated with high protein intake. Those with a high protein intake were far less likely to develop cancer than those on low protein diets.
These are early days yet, and it is likely to be some time before any clear dietary recommendations can emerge. Much of the current advice for slowing the ageing process is based on having a good intake of antioxidants, dietary fibre and omega-3 fatty acids.
Antioxidants are purported to help moderate DNA damage – genetic mutations and chromosome damage – which can build over time and gradually disable more and more cells. Dietary fibre helps to moderate things such as the sugar and fats in our blood, as well as helping to maintain a healthy bowel. Omega-3 fatty acids are ‘good’ fats, for which many unproved claims are made, and even the case for promoting heart health is debated.
Does improving health through diet increase longevity? Having healthy heart and bowels may not protect us from the inevitable march of cumulative DNA and chromosome damage. Even the link between free radicals and antioxidants may not lengthen life.
It seems we have a long way to go before we can stop ageing in its tracks, but I suspect that many of us would opt for a moderately long and healthy life rather than simply a very long life.