Active Voice: Diet Manipulation for Healthy Living - Importance of 16-Hour Fasting
By: Antonio Paoli, M.D., FACSM, FECSS

Social media commonly offers a variety of healthy living solutions, presenting a perfect mix of speculation, firm belief, a bit of scientific evidence and personal experience. Nutrition tends to be a popular topic on social media. Often, a seemingly convincing case is made that encourages people that a dietary approach is miraculous. One such topic is prolonged fasting. As health practitioners, we often have clients mention this “new” approach to healthy living. However, the approach often has little-to-no scientific evidence.

Our group recently completed a project studying prolonged fasting. Our study, published in the December 2021 issue of Medicine & Science in Sports & Exercise®, evaluated the effects of daily diet manipulation and resistance training on health benefits. We hypothesized that 12 months of time-restricted eating would lead to lower fat body mass and a reduction of inflammatory and metabolic markers compared to a regular dietary pattern. This diet manipulation experiment was conducted in a group of expert resistance trainers. The time-restricted eating group consumed their energy needs in three meals during eight hours each day. Subjects in the normal diet group also had three meals, which were consumed over 16 hours. This approach provided fasting times of 16 and eight hours, respectively. The time-restricted eating group calories distribution was 40% at the first meal (“break the fast”), 25% at the second meal and 35% at the last meal.

After 12 months of daily fasting for 16 hours, the experimental group showed losses of 3.3% body mass and 11.8% body fat mass. The normal diet group showed gains of 3.4% and 2.9% of body mass and fat mass, respectively. The visceral adipose tissue measured via dual-energy x-ray absorptiometry decreased by 18.8% in the experimental group.

Interestingly, the long-term fasting period impacted the testosterone levels of participants, inducing a 16.8% reduction within the experimental group, while no change was observed in the normal diet group. Furthermore, the same trend was observed for insulin-like growth factor 1. The fasting protocol also had an impact on the cholesterol profile and insulin resistance, which improved significantly, and inflammatory markers, which decreased by more than 13% in 12 months.

These findings demonstrated that well-trained resistance exercisers who adhere to a fasting protocol for a long period of time can obtain beneficial effects on health biomarkers and inflammatory indices. Moreover, the long-term time-restricted eating approach spontaneously reduced the total caloric intake, driving a “healthy weight loss.” However, long-term, time-restricted eating negatively affected muscle mass due to the significant negative impact reported on anabolic hormones in this population.

Our study provides new insight into the management of meal frequency and meal timing for people expert in resistance training activities. The main take-home message is that there are pros and cons to prolonged time-restricted eating. Although time-restricted eating may produce some physiological advantages, it is not a miracle as often suggested in social media posts.

About the author:
Antonio Paoli, M.D., FACSM, FECSS, is a professor and dean of Sport and Exercise Sciences at the University of Padua in Italy. He earned a B.S. in Physical Education (ISEF) from the University of Bologna (Italy) and his medical degree from the University of Padova. In 2008, he obtained a specialization in sport medicine from the University of Pavia. Dr. Paoli also serves as a professor and chair of Strength Training and Sport Nutrition at the University UCAM (Murcia, Spain) and as the president of the Italian Society of Sport and Exercise Science (SISMES) and the European Sport Nutrition Society (ESNS). His current major research directions include the interaction of exercise and diet, mainly ketogenic diet and time-restricted-eating, the molecular bases of exercise training adaptation and the effects of different methodology of resistance training on health parameters and body composition in young and adults.

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily represent positions or policies of ACSM. Active Voice authors who have received financial or other considerations from a commercial entity associated with their topic must disclose such relationships at the time they accept an invitation to write for SMB.