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Intermittent fasting, timing of exercise can impact metabolic health


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Krista A. Varady, PhD
Krista A. Varady, PhD

Intermittent fasting can be as effective as calorie restriction in helping people lose weight and experience important metabolic changes, though the type of fasting employed does make a difference.

Such was the conclusion of Krista A. Varady, PhD, Professor of Kinesiology and Nutrition at the University of Illinois College of Medicine, who explained the various forms of intermittent fasting and their effects compared to more traditional diets during the session, Timing of Eating and Exercise in Metabolic Health, on Saturday, June 4.

The session was livestreamed and can be viewed on-demand by registered meeting attendees at If you haven’t registered for the 82nd Scientific Sessions, register today to access the valuable meeting content.

Dr. Varady presented a 12-week study of four groups of people who fasted on alternate days, exercised four or five days a week but did not fast, exercised four or five days a week and fasted on alternate days, or did nothing.

The exercise/fasting group saw a reduction of liver fat of about 5.5%, which wasn’t significantly different from the fasting-only group, she said. The exercise-only and control groups saw no significant changes.

Lisa Chow, MD, MS
Lisa Chow, MD, MS

The combination group also saw fasting insulin and insulin resistance decrease, insulin sensitivity increase, and waist circumferences decrease, indicating that visceral fat mass went down.

Dr. Varady also discussed the intermittent fasting methods people are best able to adhere to.

Between 30-40% of alternate-day fasting participants in one study dropped out in the first three months. Adherence was much higher with time-restricted eating (TRE)—eating each day during a set four- to eight-hour period—particularly when participants ate later in the day. Those dieters lost only about half as much weight in the first three months compared to those who did alternate-day fasting or traditional diets.

“I think people (are) sick of counting carbs or buying high-protein bars,” she said. “They want to do something that’s way simpler.”

Lisa Chow, MD, MS, Professor of Medicine, Division of Diabetes, Endocrinology, and Metabolism at the University of Minnesota, pointed to a recent year-long study in China of 140 participants who either had their calorie intake decreased by 25% or did TRE. It found that both groups lost a significant amount of weight after a year, and their metabolic measures improved significantly, including blood pressure, cholesterol, and glycemic levels. From this, researchers concluded that TRE was similarly effective in reducing weight, body fat, and metabolic risk factors as daily calorie restriction.

Dr. Chow also discussed how study participants adhered to fasting and tracked and reported their eating.

Leonidas Lundell, PhD
Leonidas Lundell, PhD

“Even if you tell people to restrict to eight hours, they probably only restrict to 10 hours, and that’s actually really important to consider,” Dr. Chow said. “People don’t quite do what you tell them to do, so you have to track and to account for that.”

She recommended daily compliance monitoring, such as first and last meals, coupled with a 24-hour dietary recall.

Leonidas Lundell, PhD, Bioinformatician and Data Scientist at the University of Copenhagen, discussed tuning one’s circadian clock through exercise and TRE.

One study of mice found exercising later in the active period of their daily circadian rhythm allowed them to exercise more and decreased their glucose levels compared to exercising earlier in their active time each day, he said. Other studies of mice have found meal timing also impacts metabolism and changes circadian rhythms, leading to the conclusion that circadian clocks and food timing may play an important role in human health and that the rhythms reside in the fuels rather than the clocks.

“We also see that time-restricted feeding does not alter skeletal muscle peripheral clocks, time-restricted feeding induces a large number of rhythmic metabolites in the serum and skeletal muscle transcripts, and finally, the time-restricted feeding alters rhythmicity of lipid- and amino acid-related metabolites.”

Vishwa Deep Dixit, DVM, PhD
Vishwa Deep Dixit, DVM, PhD

Vishwa Deep Dixit, DVM, PhD, Director, Yale Center for Research on Aging, Yale School of Medicine, spoke about how caloric restriction induces immunological reprogramming in humans.

He cited CALERIE Phase II, a controlled randomized trial that restricted the calorie intake of healthy people by about 15% for two years to learn the effects on adipose tissue, which serves as an immunologic organ because it’s full of hematopoietic cells.

Researchers found that calorie restriction altered transcriptional regulation, the means by which cells regulate the conversion of DNA to RNA.

“A simple reduction in calories without any change in macronutrient intake in free living people is pretty darn effective,” Dr. Dixit said.

They also found that secreted protein acidic and rich in cysteine (SPARC) was expressed close to four times higher than leptin.

SPARC, a metabolically regulated adipokine, is inhibited by caloric restriction, Dr. Dixit noted.

“It is not just a passenger, but in fact it is a driver of the responses of CR because if you lower production from fat cells specifically, you lower inflammation because of SPARC’s action on macrophages,” he said.