Caloric restriction is the most reliable intervention to prevent age-related disorders and extend lifespan. The reduction of calories by 10-30% compared to a normal (ad libitum) diet is known to extend the longevity of various species from yeast to rodents. The underlying mechanisms, why caloric restriction extends the life span have not yet fully been understood.
The benefits of caloric restriction are related to the metabolic rate and reactive oxygen species
Recent scientific studies indicate that the benefits of caloric restriction are related to changes in the metabolic rate as well as the accumulation of reactive oxygen species. It is widely believed that caloric restriction delays the onset of age-related decline in many species, as well as the incidence of age-related diseases such as cancer, diabetes, atherosclerosis, cardiovascular disease, and neurodegenerative diseases.
Caloric restriction affects the behavior, animal physiology, and metabolic activities such as modulation of hyperglycemia and hyperinsulinemia, as well as increases insulin sensitivity.
Limiting the number of calories while avoiding malnutrition
Caloric restriction means limiting the number of calories consumed each day while avoiding malnutrition. Restricting calories extends life and reduces age-related chronic disease in many organisms. These effects have been observed in a wide range of animal models, including mammals.
When caloric intake is low, during what’s known as a fasting state, cells switch into protective mode. They activate processes that rejuvenate themselves and defend against potential threats and stressors. These changes have long-term benefits for overall health, and possibly for life extension as well.
On the flip side is the dietary excess plaguing modern societies. This chronic, surplus calorie ingestion contributes to a variety of health problems. Surging rates of obesity, type II diabetes, neurodegenerative disorders, and cancer have all been linked to excessive calorie intake.
History of caloric restriction studies
The first experimental evidence of the effects of food restriction on lifespan was provided in the early 1900s when two independent studies confirmed that the restriction of food intake of rats retarded their growth, but prolonged their lifespan.
The most noted study of the effects of caloric restriction was conducted in 1935 when a group of researchers showed that restriction of food intake by 40% from the age of weaning extended the lifespan of rat by up to two times. Their findings were confirmed by a series of experiments conducted in 1986.
To date, the effects of caloric restriction on lifespan and health had been demonstrated in many model animals from yeast to mammals. Owing to ethical and experimental limitations, investigations of human caloric restriction have not been actively conducted. As a result, studies of the benefits of caloric restriction on humans have primarily been restricted to epidemiological studies.
A representative experimental study of human caloric restriction is the CALERIE (Comprehensive Assessment of Long Term Effects of Reducing Caloric Intake) program, in which healthy volunteers underwent the caloric restriction interventions for 2 years. The CALERIE groups have published several reports showing the benefits of caloric restriction on anti-aging, including increased insulin sensitivity, improvement of plasma lipid composition, and attenuation of oxidative stress.