Might eating less help us live longer? What evidence is there? Are there any health risks if we eat less?
What can we learn from experiments with animals?
Could a very low calorie diet be the key to a long and healthy life? This is what a Science Daily article in 2014 suggested.
For many years now there has been evidence that reducing the food available to a number of different species (calorific restriction) results in their living longer. However, this has usually been found in studies with mice or fruit flies in the controlled conditions of a laboratory.
Human beings differ from mice and fruit flies in a number of important respects – and their everyday lives are affected by a wider range of factors than animals in a laboratory. So can eating less help humans live longer?
Studies in monkeys are probably a more valuable source of research. They live longer than laboratory animals and are biologically closer to humans. One study found that rhesus monkeys lived longer if they ate moderately less. However, another study found that eating less made no difference to the monkeys’ longevity.
What both studies agreed is that eating less resulted in healthier monkeys. The first study showed lower levels of cancer, cardiovascular disease, diabetes and brain deterioration. The second found a statistically significant reduction in cancer and a less significant delay in the onset of diabetes, arthritis and cardiovascular problems.
When the two studies were reviewed, in an article published in Nature in 2017, the authors concluded that the benefits of calorie restriction extended to diseases that are among the most prevalent in human clinical care including cancer, cardiovascular disease and parameters associated with diabetes.
Might this still work in humans?
Some human population studies suggest a similar picture. For example in Japan, people living on the island of Okinawa and following a traditional lifestyle have some of the longest life expectancy in the world. Part of this traditional lifestyle involves eating only until you are 80% full which is known as Hari Hachi Bu. This is only one of a number of potential factors. Exercise, the quality of their largely plant based diet and their social lives are others. However it suggests a possible association between humans eating less and living longer. And when Okinawans have adopted a Western lifestyle (including larger portions) they haven’t lived as long.
Why calorific restriction might work is still being researched and debated. For example biological, evolutionary and genetic factors have all been suggested.
However, what we do know is that it typically extends the lifespan of some species researched so far and seems to provide some protection against age related disease in monkeys (a species closer to humans). Population studies (in particular in Okinawa) and small scale studies in humans suggest it may help increase human longevity, as part of a healthy lifestyle.
The risks of eating too little
Eating less may help us live longer but it is important to ensure we get the right quality and quantity of food.
Anorexia illustrates what can happen if people eat too little. Anorexics are at increased risk of cardiovascular problems, coronary heart disease, damaged bones, anaemia, kidney failure and liver damage.
Simply being seriously underweight (presumably linked to eating less) can limit longevity.
This is a ‘half way house’ i.e. restricting how much you eat for one or two days a week. It has been suggested that this is more beneficial to ageing as it carries less of the health risks associated with chronic calorie restriction.
A review of the limited evidence available, published in 2015, found potential health benefits but argued that significantly more research was needed before intermittent fasting could be recommended.
The Mayo Clinic agrees there may be health benefits but also advises against fasting and exercising at the same time (to avoid potential dizziness), fasting while taking diabetic medication (as this may lead to serious health issues) and skipping breakfast (as this has been associated with an increased risk of obesity).
Life span or health span?
How long we live isn’t the only issue. How long we stay healthy (rather than spending years burdened with chronic illness) is another.
Whether or not eating less adds years to our life, most evidence suggests it is a healthy option, reducing the risk of a range of chronic illnesses.
- How much we eat and its nutritional value is one factor potentially affecting human longevity.
- Other factors include how much exercise we take, our genes, whether we smoke or drink a lot of alcohol, our occupation and interests, our personality and our social life.
- However, eating too much or too little is bad for our health. It could make us more susceptible to chronic illness - and may even knock years off our lives.
- If we are aiming to eat less we need to ensure we eat a healthy diet, to get enough vitamins, minerals and nutrients.
Christiane Hahne, Reviewed October 2017, next Review date September 2020.