Benefits of Intermittent Fasting

By Dr. Paul E. Lemanski, MD, MS, FACP

Medicines are a mainstay of American life and the healthcare system, not only because they are perceived to work by the individuals taking them, but also because their benefit may be shown by the objective assessment of scientific study. Clinical research trials have shown that some of the medicines of Western science may reduce the risk of heart attacks, strokes and cardiovascular death, while others may reduce certain types of cancer.

In the first 84 installments of the Non-Medicated Life, informed diet and lifestyle have been shown to accomplish naturally for the majority of individuals, many, if not most of the benefits of medications in the prevention and treatment of chronic medical conditions. Moreover, as a medical intervention they may accomplish such benefits with fewer side effects, may reduce the number and amount of medication, and may allow actual discontinuation of medication. An informed lifestyle is one that avoids unnecessary health risks and promotes healthy behaviors including adequate rest and daily exercise.

An informed diet is one with a special, defined composition and caloric content. However, it is not only the number and the composition of those calories that prove critical to health. More recently, the timing of when you eat and don’t eat (fasts) may also be shown to contribute significant benefit. Indeed, intermittent fasting and a variation called early time restricted feeding may aid in weight reduction, improve insulin resistance, and lower both blood sugar and blood pressure.

Fasting can be defined as a voluntary restriction of all caloric intake for a specified time. Water and non-caloric liquids such as tea may be consumed during the fast in order to maintain adequate hydration. Fasting has been used for thousands of years in certain religious practices. More recently fasting has been promoted as a means of rapid weight loss for individuals who are overweight or obese. However, all fasts are not the same. For the reasons described below, fasts of different lengths differ in benefits and drawbacks, when compared with simply reducing caloric intake during the same time period.

Fasting is conceptually simple to implement and the weight loss is rapid. Moreover, after 72 hours of fasting, appetite is suppressed and the fast actually becomes easier to maintain. The liver can store 8-12 hours of glucose in a form combined with water called glycogen. While we sleep, this glycogen is broke down and supplied to the blood stream as glucose, which is the main energy source used by the brain. When we awaken in the morning we break the fast and eat to resupply liver stores. However, if we do not eat and extend the fast beyond 8-12 hours, certain biochemical changes begin to occur elsewhere in the body. Glycogen is also stored in muscles, and as depletion of liver glycogen progresses, blood sugar levels fall and muscle glycogen is broken down to supply glucose to the brain. The reduced blood sugar lowers insulin levels, and in those with diabetes or pre-diabetes helps reverse insulin resistance, which is the root cause of diabetes.

The problems with fasting, however, extend beyond the initial feelings of hunger, stomach discomfort and weakness, with which most of us are familiar. As the fast progresses to about 72 hours, muscle glycogen in turn becomes depleted, and fat is used as the main energy source. The brain switches its primary energy source from glucose to breakdown products of fat metabolism in a process called starvation ketosis. Additionally, some glucose may be produced from breakdown of the body’s protein reserves. Thus, one unfortunate consequence of fasting is loss of muscle. Indeed, during a prolonged fast for every two pounds of weight loss, one pound comes from fat and one pound comes from your own muscle – certainly not a desirable outcome.

Loss of muscle mass may be reduced, while still allowing weight loss and lower insulin and blood sugar levels, by the practice of intermittent fasting (IF). One example of IF is alternate day fasting during, which no calories are consumed on fasting days that alternate with unrestricted caloric intake on feeding days. In animal models, such an approach was equivalent to simple caloric restriction in reducing body weight, insulin levels and blood sugar. Studies in humans confirmed the efficacy, but the length of fasting was insufficient to reduce hunger, and thus alternate day fasting at least as a long term practical strategy is difficult to maintain. However, another variant of IF called early time restricted feeding (ETRF) may be both effective and practical long term.

Early time restricted feeding is a strategy of restricting all caloric intake for a 24-hour day to a limited period of the day. In addition, the timing of intake is also linked to the body’s normal circadian rhythm. In one ETRF study of rats fed a high fat diet, restricting calories to eight hours protected against obesity, fatty liver, and increased insulin levels – as compared to animals fed the same diet without time restriction.

In one ETRF study in pre-diabetic men, participants were randomized to receive all meals during an eight-hour period, either from 7am to 3pm or a 12-hour period from 7am to 7pm. Both groups were fed sufficient calories to maintain weight. Interestingly, those confining calories to an eight-hour period had lower insulin levels, improved insulin sensitivity, lower blood pressure, and a reduced appetite. Other human studies employing ETRF found that simply a prolonged duration of nighttime fasting, without a restriction in calories, resulted in 2-4% lower body weight. Because of these significant effects, those with diabetes (especially those taking medications) who are interested in trying ETRF, before starting should discuss planned implementation with their personal physician and a registered dietitian or certified diabetes educator.

In summary, it is becoming increasingly clear that information about the composition and the caloric content of the diet are not the only ways to make diets healthier. Indeed, the timing of food consumption, together with a prolonged daily period of fasting appears to be important as well. By practicing a variant of IF known as ETRF and restricting caloric intake to an 8-10 hour period, individuals may lose modest weight without hunger, lower blood sugar, improve insulin sensitivity, and lower blood pressure – all without restricting total calories. In this way, informed diet with intermittent fast may be shown to contribute significantly to living the Non-Medicated Life.

Paul E. Lemanski, MD, MS, FACP (plemanski@capcare.com) is a board certified internist at Center for Preventive Medicine at Community Care Physicians in Albany. He is medical director of the Dept. of Community Medicine and Population Health at Community Care Physicians. Paul has a master’s degree in human nutrition, he’s an assistant clinical professor of medicine at Albany Medical College, and a fellow of the American College of Physicians.