As Dr Sarah Brewer, Medical Director at Healthspan explained to Express.co.uk, animal studies suggest prolonged calorie restriction can extend lifespan but how far these findings can be extrapolated to humans is unknown.
“The strongest evidence comes from inhabitants of Okinawa island in Japan, where there are five times more centenarians compared with other industrialised countries,” she said.
“In Japan, longevity is sought through a philosophy of dietary restriction known as ‘hara hachi bu’ which translates as ‘eight parts out of 10’ – in other words, practitioners aim to eat only until they are 80 percent full.”
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As she explained, the 80 percent full rule appears to be sufficient to activate SIRT1 production – a protein which promotes the long-term survival of irreplaceable cells by increasing free radical protection.
“If the gene that codes for SIRT1 is switched off or deleted then calorie restriction does not extend lifespans.”
Conversely, as Dr Brewer explained, if the SIRT1 gene is switched on then lifespan is extended.
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One study published in the Cell Metabolism journal this month concluded that cutting calorie intake by 15 percent over two years can slow ageing and protect against diseases such as cancer, diabetes, and Alzheimer’s.
A different, more extreme calorie-restricted diet study published in Science Translational Medicine showed that so-called “fasting-mimicking” diets practiced for five days a month for three months can also help the body with ageing.
There are some important considerations, however.
“Do not follow a very low calorie diet unless a GP has suggested it to you,” warns the health body.
Also, very low calorie diets are less likely to be nutritionally complete as they provide far fewer calories than needed to maintain a healthy weight, it notes.
Very low calorie diets are not suitable if you are:
- Under 18
- Have had an eating disorder.
“You might already know which foods are healthy and unhealthy – but in practice it can be hard to break old habits,” says Bupa.
One handy tip is to try to stick to regular, planned meal times.
“If you feel hungry between meals, try having a glass of water and waiting 20 minutes to see if you still feel hungry,” advises Bupa.