The secret to long life expectancy is to follow a healthy lifestyle - regularly exercising, limiting alcohol intake, not smoking and eating a healthy balanced diet. When it comes to eating a healthy diet, the NHS recommends eating at least five portions of a variety of fruit and vegetables every day, basing meals on higher fibre starchy foods like potatoes, bread, rice or pasta, having some dairy or dairy alternatives, some protein, choosing unsaturated oils and spreads, and eating them in small amounts, and drinking plenty of fluids.
Many diet plans incorporate these elements of healthy eating, but with so many diets to choose from - from vegan to keto - which one can help people live longer?
Research carried out on humans indicates calorie-restricted diets can slow down the ageing process and increase longevity.
One study published in Cell Metabolism journal concluded cutting calorie intake by 15 percent over two years can also ageing and protect against diseases like cancer, diabetes and dementia.
The diets work by helping slow the metabolic rate and reducing free radicals linked to chronic illnesses.
How to live longer: The surprising food you could eat every day for a longer lifeHow to live longer: What's the best diet to increase life expectancy? (Image: GETTY)
A total of 53 healthy, non-obese people between the ages of 21 and 50 took part in the study.
Researchers said they discovered even people who are healthy and lean can benefit from following calorie-restricted diets.
Another study published in Science Translational Medicine also showed an extreme calorie-restricted diet, practiced for five days a month for three months, help the body with ageing.
The diet used was plant based and included energy bars and vegetable soups.
Another study published in Nature Communications showed calorie-restricted diets carried health benefits for monkeys.
And another study done at Washington University School of Medicine in St Louis indicated some animals lived up to 50 percent longer after significantly cutting calories.
The diets, whether started early or in midlife in animals, can increase longevity, according to researchers.
How many calories a day are recommended?
As a guide, the NHS says an average man needs around 2,500kcal (10,500kJ) a day to maintain a healthy body weight.How to live longer: A calorie restricted diet has been proven effective (Image: GETTY)
For an average woman, that figure is around 2,000kcal (8,400kj) a day.
But these values can vary depending on age, size and levels of physical activity, among other factors.
With many low calorie diets, people get between 800 and 1,500 calories a day.
Eating 800 calories a day for fewer is considered a “very low calorie diet (VLCD)” and should be clinically supervised.How to live longer: A very low calorie diet is typically for adults who are obese (Image: GETTY)
The NHS explains: “VLCDs are typically for adults who are obese – defined as having a BMI over 30 – but should not be the first option to manage obesity.
“These diets should only be followed under medical supervision for a maximum of 12 weeks continuously, or intermittently with a low-calorie diet – for example, for two to four days a week.
“Most people who want to lose weight do not need to follow a very low calorie diet.”