Scientists are searching for drugs that might extend human lifespan and healthspan (the number of years spent in good health, free of chronic diseases of ageing). We tend to draw a hard line between food and drugs, yet according to dictionary definitions, a drug is ”a medicine or other substance which has a physiological effect when ingested or otherwise introduced into the body”. Most of the foods we eat on a daily basis contain hundreds or thousands of distinct chemicals that would fall under this definition, and so anyone seeking to live for as long as possible and in good health should really have food towards the top of their list of priorities.
Research has shown that calorie restriction or CR (a sharp reduction in calorie intake to below daily calorie expenditure, but without causing malnutrition) and various forms of fasting can significantly extend the maximum lifespan of many different animals. Whether this works in humans is uncertain, but research suggests that these practices can at the very least reduce the risk of age-related diseases, allowing humans to live in good health for longer. However, you can’t stay on a diet that puts you at a calorie deficit forever: you will eventually begin to starve. So, what should you eat when you are not fasting or practicing CR? You’ll struggle to find a definitive answer to this question that is backed up by science.
Of course, there are guidelines: eat at least 5 different fruits and vegetables per day, restrict intake of free sugars, avoid trans fats, minimise saturated fats and so on. But that’s not good enough for those seeking to beat Jeanne Calment’s record. There is presumably an optimal human diet – a combination of dietary components that will act on the molecular mechanisms of ageing in the most desirable way. This ”longevity diet” would give us the best chance of ageing as slowly as possible.
Despite extensive research, the optimal combination of nutrients for human longevity is a controversial topic. That’s partly because it’s not just about what you eat, but when you eat it, how old you are, whether you are male or female, what genes you have, your body composition, the state of your gut microbiome and more. Diet interacts with all of these factors in a complex way, and so trying to extract an optimal diet from a mountain of scientific studies on isolated nutrients, many of them observational in nature, is difficult.
Recently, an article was published in the journal Cell in which researchers attempted to home in on an optimal diet for human health. They did this by reviewing hundreds of articles using what they refer to as a ‘multi-pillar approach’, taking into account the four pillars of epidemiological studies (relating diet to health and disease), simple longevity studies (relating diet to healthspan and lifespan), clinical trials and studies of populations with exceptional longevity. They took into account evidence from both animal and human studies, and also reviewed the main calorie restriction and fasting strategies, as well as the molecular mechanisms by which diet is thought to interact with the ageing process. Taking all this into account, they attempted a rough outline of what might constitute an optimal diet for longevity in humans:
How much longer might you expect to live by adopting such a diet? A recent study based on meta-analyses form the Global Burden of Disease 2019 study, which includes studies from the United States, China, and Europe, gives us an idea. Changing from the typical Western diet to one rich in legumes, whole grains, and nuts with reduced red and processed meats was associated with an increase in life expectancy. On average, women lived 10.7 years longer, while men lived 13 years longer if the diet was adopted at age 20. If started at age 60, both men and women still gained over 8 years of increased life expectancy.
You’ll notice that the above guidelines are still vague when it comes to exact quantities of most dietary components. That’s because there’s still no well supported answer to this question, and there probably isn’t going to be one any time soon. A more coordinated scientific effort, with large clinical trials of diets such as this one, might bring us closer.
Nutrition, longevity and disease: From molecular mechanisms to interventions: https://doi.org/10.1016/j.cell.2022.04.002