Back in 1989 a study got started on 76 adult rhesus monkeys to find out if reducing caloric intake over a long period of time had a beneficial or detrimental impact on the monkeys. After 20 years, researchers discovered that the monkeys with the lowest caloric intake lived the longest. Only 13% of the calorie-restricted monkeys died during the study period compared to 37% of the non-restricted monkeys who died during the same period. Calories were reduced by about 30% to 50% and were boosted by vitamin and mineral supplements. The calorie-restricted monkeys also had less brain shrinkage, less body fat and less loss of muscle.