Like many people, you probably associate the term “intermittent fasting” with losing weight. But such restricted eating plans have demonstrated many health benefits beyond weight loss. Different patterns of intermittent fasting are being studied for their potential to maintain good health and promote a longer life.
Studies in animals and people suggest that periodic cycles of fasting may improve certain metabolic and immune functions.1 Some research has even indicated that intermittent fasting programs can protect against health issues like cardiovascular disease.2
Calorie restriction focuses solely on setting a regular pattern of reduced average caloric consumption. Intermittent fasting includes a range of recurring eating patterns in which individuals go anywhere from 16 to 48 hours with little or no caloric intake, interspersed with periods of normal eating.2 While fasting diets primarily focus on the frequency of eating rather than the amount being consumed, they sometimes incorporate calorie restriction during non-fasting times.
Intermittent fasting improves health and counteracts disease processes through the activation of adaptive cellular stress response signaling pathways. This activation enhances mitochondrial health; DNA repair; and autophagy, the body’s mechanism for getting rid of damaged cells. Intermittent fasting can increase the resistance of the body’s cells, tissues, and organs to stress. Periodic fasting also promotes stem cell-based regeneration as well as long-lasting metabolic effects.2
Research has revealed that during fasting, the body first uses up glucose and glycogen, then starts to burn energy reserves stored in fat. This stored energy is released in the form of chemicals called ketones, which allow cells—particularly brain cells—to continue working at full capacity. Some researchers believe that because ketones are a more efficient energy source than glucose, they may protect against age-related central nervous system decline that could cause dementia and other disorders.3
In normal and overweight human subjects, studies of various intermittent fasting regimens have demonstrated effective weight loss and improvements in multiple health indicators including insulin resistance, as well as reductions in risk factors for cardiovascular disease.2
Women participating in a large randomized comparison of intermittent energy restriction and continuous energy restriction plans were able to achieve comparable weight loss and improvements in a number of risk markers for cancer, diabetes, and cardiovascular disease.4
But the benefits of intermittent fasting may go beyond weight-related concerns. In studies of laboratory rats and mice, intermittent and periodic fasting diets have shown the ability to counteract disease processes and improve functional outcomes in experimental models of a wide range of age-related disorders including diabetes, cardiovascular disease, and cancers, as well as neurological disorders such as Alzheimer’s disease, Parkinson’s disease, and stroke.2
In mice, bimonthly fast-mimicking diet (FMD) cycles of 4 days started at middle age extended longevity, lowered visceral fat, reduced cancer incidence and skin lesions, rejuvenated the immune system, and slowed bone mineral density loss. And in elderly mice, FMD cycles improved cognitive performance.1
Results of a year-long randomized non-inferiority trial comparing intermittent and continuous fasting schedules showed that both produced reductions in hemoglobin A1C levels in patients with type 2 diabetes. Participants on the intermittent fasting plan also reported an average weight loss of 15 pounds.5
A small study of patients with cancer undergoing chemotherapy suggests that short-term fasting can reduce chemotherapy-associated side effects, although it isn’t clear whether it had any impact on the cancer itself.6 And in a pilot clinical trial in human subjects, three FMD cycles lowered biomarkers for aging, diabetes, cardiovascular disease, and cancer without major adverse effects.1
Most calorie-restriction and fasting-diet studies have been in younger people, but researchers are beginning to study the effects of intermittent fasting diets in older adults. One ongoing clinical trial is testing the 5:2 diet in obese people ages 55 to 70 with insulin resistance, a condition that can lead to diabetes. The study is designed to find out whether eight weeks of the 5:2 diet affects insulin resistance, as well as its impact on the brain chemicals that play a role in Alzheimer's disease.3,7
If you are tempted to try intermittent fasting, bear in mind that evidence is still being gathered as to its safety and effectiveness. Before changing your eating regimen, talk with a healthcare professional about the benefits and risks of intermittent fasting, and make sure the eating plan you choose is providing you with enough nutrition.