Intermittent Fasting

Ask the DOC

Glucose, a simple sugar, is the fuel that powers most mammals, humans included. All foods that we consume are broken down in the digestive tract by digestive enzymes to simple nutrients including glucose. At approximately eight to 12 hours after the last food intake, assuming there is no oral intake after that, the body has used all the available glucose from that meal, so it must find glucose from another source. The body then begins a process in the liver called gluconeogenesis, which breaks down fatty acids to make glucose. This process creates ketone bodies, which can be found in the urine of a fasting person. In a starvation scenario, after the body runs out of fatty acids, it breaks down proteins, including muscle proteins, to make glucose. This entire process can be found in a biochemical formula called the Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid cycle.

Traditionally, we have been taught that proper nutrition requires the consumption of three meals a day (“three squares a day”). We have also been admonished not to skip meals. While this is good advice for some, especially diabetics, recent research has started to question the wisdom of this advice. A dietary approach called intermittent fasting, which limits food intake for extended periods of time, has begun to receive more attention. This dietary approach has been used for attempts at weight loss, for other health objectives, or as part of some religious practices. It involves skipping meals, time-restricted fasting (such as 16 – 24 hours of fasting), or intermittent full-day fasting on two to four days a week. As described above, intermittent fasting triggers gluconeogenesis, which involves the breakdown of body fat. Studies have shown that intermittent fasting decreases blood inflammatory markers and improves glucose regulation.

Studies have also shown that when compared to a daily calorie-restricted diet, intermittent fasting is not more effective in terms of weight loss and is more difficult to adhere to, however intermittent fasting has been shown to decrease blood pressure, resting heart rate, cholesterol and triglyceride, glucose, and insulin. While these improvements in cardiovascular risk factors typically begin within two to four weeks of starting an intermittent fasting diet, they dissipate within several weeks of resuming a normal diet. Intermittent fasting may produce side effects such as weakness, hunger, dehydration, headaches, difficulty concentrating, low blood pressure, or fainting. It is not recommended for pregnant or lactating women, frail older adults, individuals with immune system issues, or those with or at risk of eating disorders. Anyone considering starting an intermittent fasting diet should first discuss the risks and benefits with their doctor and/or nutritionist. It is not recommended for those with diabetes because of the risk of low blood sugar (hypoglycemia).

For more information go to the National Library of Medicine at:

Questions and comments may be sent to This email address is being protected from spambots. You need JavaScript enabled to view it..

By Peter Galvin, MG

Sign up via our free email subscription service to receive notifications when new information is available.