They believe eating about 20 per cent less than the recommended daily intake will extend their lifespans and help them avoid getting sick.
Evidence shows animals given fewer calories, or kilojoules, have longer life expectancies than those that eat an average amount.
Calorie restriction may also reduce the risk of heart disease, diabetes and some cancers.
However, critics warn people who drastically restrict their diets may be more likely to develop eating disorders, nutritional deficiencies and fertility problems.
