Several prior studies have indicated that calorie counting may offer long-term benefits compared to intermittent fasting. After one year, both approaches led to approximately a 5 percent reduction in body weight, but intermittent fasting may enhance insulin sensitivity.
Over the past decade, intermittent fasting, where individuals refrain from eating for specific periods during the day or week, has gained significant popularity as a weight-loss method. Many of these fasting regimens do not necessitate calorie counting, which appeals to numerous dieters. However, it’s crucial to avoid overeating during eating windows, as excessive consumption can hinder weight loss.
Despite arguments from some researchers favoring traditional calorie tracking as a more effective and established weight loss method, a recent study published in the Annals of Internal Medicine this week suggests that time-restricted eating could yield comparable outcomes.
“We found that people can just count time instead of counting calories and achieve the same reduction in calories and the same weight loss,” Krista Varady, PhD, said. She is a professor of nutrition at the University of Illinois in Chicago.
“For some people, it’s just much easier, and hopefully in the long term, they may be able to stick to that plan better than tedious daily calorie counting.”
Losing Weight Sans Calorie Counting
In a study comparing intermittent fasting to calorie restriction, Dr. Varady and her research team monitored 90 obese adults in the Chicago area, with 77 of them completing the study. The participants were a diverse group in terms of race (Black, Hispanic, Asian, and white), with approximately 80 percent being female, and an average age of 44.
The participants were randomly assigned to one of three different plans:
- Eating as much as desired but restricting food consumption to an eight-hour window (from noon to 8 p.m.).
- Counting calories and reducing their usual calorie intake by 25 percent.
- Serving as a control group, maintaining their regular eating habits (consuming food over a period of 10 or more hours per day).
For the first six months of the study, both the calorie-restricted and intermittent fasting groups had regular meetings with a dietitian, and for the following six months, these meetings occurred biweekly. The dietary counseling aimed to promote healthier eating habits, such as increasing fruit and vegetable consumption while reducing soda and alcohol intake. All participants were instructed not to alter their exercise routines.
After one year, both the intermittent fasting and calorie-restricted groups achieved similar outcomes. When compared to the control group, those who practiced intermittent fasting without calorie tracking reduced their daily calorie intake by an average of 425 calories and lost approximately 10 pounds more weight. Meanwhile, those in the calorie-counting group decreased their daily calorie intake by an average of 405 calories and lost nearly 12 pounds compared to the control group.
On average, participants in both the intermittent fasting and calorie-restricted groups lost 5 percent of their body weight. According to Varady, shortening the eating window naturally led to a reduction in calorie consumption.
Even Minor Weight Loss Lessens Diabetes and Heart Disease Risks
“The amount of weight lost indicates that behavioral approaches can work,” David Creel, PhD, RD, said. He is a psychologist and registered dietitian at Cleveland Clinic.
Dr. Creel, who was not part of the study, highlights that even a relatively modest reduction in weight can yield significant health advantages. Findings from the Washington University School of Medicine in St. Louis suggest that a 5 percent decrease in body weight can reduce the risk of diabetes and heart disease, while also enhancing metabolic function in the liver, adipose tissue, and muscle.
Nevertheless, Creel acknowledges that for many obese individuals, achieving more substantial weight loss and health improvements may require additional interventions, such as medications or bariatric (weight loss) surgery.
Intermittent Fasting May Help Boost Body’s Insulin Sensitivity
The researchers also observed enhanced insulin sensitivity in the fasting group as compared to the control group, while no such improvement was evident in the calorie-restricted group.
Impaired insulin sensitivity, commonly referred to as insulin resistance, arises when the body’s cells fail to respond effectively to insulin—a hormone secreted by the pancreas that plays a crucial role in regulating blood sugar (glucose) levels. In individuals with impaired insulin sensitivity, muscles, fat cells, and liver cells do not react appropriately to insulin, resulting in inefficient glucose uptake from the bloodstream or its storage. This condition can lead to elevated blood sugar levels and, ultimately, may increase the risk of prediabetes or type 2 diabetes, as stated by the American Diabetes Association.
“We know from prior studies that when one loses weight, your insulin sensitivity tends to improve,” said Christina C. Wee, MD. She is an associate professor of medicine at Harvard Medical School and director of the Obesity Research Program at Beth Israel Deaconess Medical Center in Boston. It also must be noted that Dr. Wee was not involved in the research.
Among the participants, the insulin sensitivity at baseline for the fasting group were worse. Varady believes that’s why improvement was only evident to those who belonged to the fasting group and not the calorie restricted group. “When somebody is more unhealthy at baseline, it’s easier to see changes in that group compared to the others,” she added.
Wee cautions against making premature judgments about the comparative benefits of each dietary approach in terms of insulin sensitivity due to the limited size of the study population.
Creel advocates for a more comprehensive and in-depth analysis that thoroughly compares the two diet plans.
“We must look at these approaches in the context of other important aspects of health,” he said. “What do people actually choose to eat during their eating window? How does it impact sleep and physical activity, and is it sustainable long term? It is clear that the body is well equipped to go longer periods without food, but how does this work for the majority of us in the context of our lifestyles?”
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