A New Look at Intermittent Fasting Suggests a Multitude of Benefits
In the September 2020 issue of Scientific American, science journalist Claudia Wallis details some important new information about the benefits of intermittent fasting (IF).
Many of us already have a basic understanding of intermittent fasting, based on decades of published work by researchers including Dr. Loren Cordain,[2,3] and the numerous, popular fasting apps. [4,5,6] In this practice, a person confines eating to certain days or certain short windows during the day.
Wallis points out the long-standing body of research in mice and rats demonstrates impressive results: lean bodies, fewer age-related diseases, and a lifespan that is 30 to 40 percent longer. However, less research has been conducted in humans.
Generally, there are three methods of intermittent fasting: alternate-day fasting, where eating a normal number of calories or a few more is allowed, followed by a restricted day of 500 or fewer calories; the 5:2 approach where normal meals are consumed five days per week, with scant meals two days per week; and the time-restricted approach in which normal meals are consumed only during certain hours each day, leaving windows of time—14, or even 16 hours each day—with no food consumption.
Within each of these scenarios, there is an opportunity for what Wallis and others term “metabolic switching.” During the fasting periods, glycogen—a stored form of carbohydrates—within cells is substantially depleted as a fuel for the body. When this occurs, the body accesses stored fats for fuel in the form of ketones, made by the liver.
According to Wallis, the benefits of intermittent fasting can go far beyond weight control and weight loss.
“In rodents and to some degree in monkeys, IF is a veritable fountain of youth, lowering body weight, blood pressure and cholesterol levels, improving glucose control, reducing systemic inflammation, maintaining brain health, and even boosting endurance and coordination,” Wallis writes.
She adds that similar results have been seen in humans, but not always. However, due to the longer lifespan of humans, it is much more difficult to conduct studies exploring the impact of intermittent fasting on longevity.
As a shining example, Wallis cited work by Krista Varady at the University of Illinois at Chicago. Varady studied the alternate-day approach, comparing it to standard calorie-cutting, and found a doubling of response to insulin—a key marker of metabolic health.
Wallis also pointed to two other studies that looked at the effects of the 5:2 approach in overweight women, comparing it to a simple calorie reduction of 25 percent. Despite similar amounts of weight loss in both groups, those who fasted displayed better blood-sugar control and lost more body fat.
Courtney Peterson of the University of Alabama at Birmingham found that pre-diabetic men who only ate during a six-hour window each day displayed better insulin sensitivity and lower blood pressure, even if they did not lose weight. 
Wallis summed up the moral of this story: These approaches can work if they are part of a permanent lifestyle change. Those changes can be difficult. Dropout rates can be high, particularly for people who use time-restriction windows.
As Varady noted, “Nobody wants to skip dinner.”
While the current research on intermittent fasting appears promising, you should always consult your personal physician before undertaking a fasting regimen to discuss the pros and cons relative to your own physique, your prescription medicines, and other metabolic considerations.
- Wallis, C. 2020. Feast and famine: intermittent fasting is the diet du jour, but many of its health claims remain unproven. Scientific American 322(4):45-49.
- Cordain L, Eaton SB, Sebastian A, Mann N, Lindeberg S, Watkins BA, et al. 2005. Origin and evolution of Western diet: health implications for the 21st century. American Journal of Clinical Nutrition 81:341–54. https://academic.oup.com/ajcn/…;
- Cordain, L. 2011. The paleo diet: lose weight and get healthy by eating the foods you were designed to eat. John Wiley and Sons, New York. 266pp.
- Anonymous. 2020. Do Fasting. https://dofasting.com/. ;
- Anonymous. 2020. Noom. https://web.noom.com/blog/2020…;
- Anonymous. 2020. Fasting application: 7 best intermittent fasting apps in 2020. https://www.spaceotechnologies…;
- Varady, K. 2020. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. DOI: 10.1016/j.cmet.2020.06.018.
- Peterson, C. 2019. Intermittent fasting research still developing, time-restricted feeding shows potential.