Heart disease, cancer, lower respiratory disease, cerebrovascular disease, Alzheimer’s disease, and diabetes account for six of the top seven causes of death in the United States in 2010. As the incidence of lifestyle-related disease continues to rise, investigations into these metabolic and cardiovascular diseases highlight the influence of obesity, insulin resistance, oxidative stress, and inflammation. Among dietary interventions aimed at halting these diseases, calorie restriction remains the most strongly supported strategy by the scientific community. However, most individuals have difficulty maintaining prolonged calorie restriction, and even initial success with daily calorie restriction has shown poor long-term results.
A growing body of evidence suggests that intermittent periods of fasting can stimulate identical biological pathways as calorie restriction. A variety of methods have been employed to stimulate fasting. The first method is termed Alternate-Day Fasting, which requires individuals to alternate between days of complete fasting and days unrestricted eating. The Five:Two method limits fasting to two days a week, allowing individuals to choose which days are most convenient for them to restrict their caloric intake. The Time-Restricted method limits fasting to a certain number of hours per day. For example, under this method, individuals would stop all food consumption after 3 pm each day. The most highly studied time restricted fast involves 16-hours of fasting with 8 hours of food consumption. Unfortunately, at this point in time, there have not been adequate head-to-head trials to evaluate the efficacy of each method, but each method has evidence supporting its use.
Beginning in 1935, when researcher Clive McCay first reported the effects of calorie restriction on lifespan and senescence, the benefits of fasting have been thoroughly applauded by the scientific community. Alternate-day fasting has been shown to be effective at reducing body weight, body fat, total cholesterol and triglycerides in normal-weight, overweight, and obese individuals. It is believed that calorie restriction increases the resistance of cells to everyday metabolic stress, such as oxidative damage. Animal models have demonstrated that mice subjected to alternate-day fasting have improved brain structures, decreased oxidative stress, and enhanced memory and learning. Other animal studies have shown that fasting can prevent the toxic effects of chemotherapy agents, allowing higher doses of treatment, and increased survival. The cardiovascular benefits using post-myocardial infarction (MI) rat models. Studies have that rats were a fed an calorie restricted diet post-MI had reduced levels of cardiac and aortic fibrosis, increased density of cardiomyocytes that were smaller in size, attenuated diastolic dysfunction, normal systolic function and arterio-ventricular coupling, compared to their non-calorie restricted counterparts. Additionally, after adjustment for body weight differences between the calorie-restricted rats and control did not effect the cardio-protective properties of the diet, signaling that the benefits of calorie restriction extend beyond simple weight loss.
Managing the sensation of hunger is one of the main reasons given by individuals for unsuccessful weight loss while dieting. Nonetheless, in small-scale studies compliance to intermittent fasting consistently remains high. To further explore this phenomenon, one study found an increase in sensations of fullness with an absence of compensatory hunger after 8 weeks of alternate day fasting. There have yet to be any long-term studies looking at the compliance and efficacy of intermittent fasting. However, because the hunger on fasting days typical does not decrease during the 8-12 week periods studied, patients may be less likely to continue this dieting strategy for an extended period of time. Future research should explore the potential benefits of long-term intermittent fasting and the feasibility of this type of dietary approach.
While a single dietary approach will not solve the complex problems involved in the current obesity epidemic, intermittent fasting may be an option to consider for targeting weight loss and improving overall metabolic status. It may be particularly useful for individuals who have difficulty adhering to commonly implemented diet plans due to eating habits, employment, or other cultural considerations. Furthermore, the simplicity of intermittent fasting allows clinicians to discuss its use as a dieting strategy in a busy clinical practice.
New York University School of Medicine
- Intermittent Fasting – the Simplest Diet for Clinical Results? - January 5, 2017
