Dieting? A New Study Found Fasting at This Hour Was More Powerful for Blood Sugar and Weight Loss Than Cutting Calories

Updated: Dec. 23, 2023

“For many people trying to lose weight, counting time is easier than counting calories," says one doctor—even allowing for a cheat day!

Maintaining a healthy weight while keeping blood sugar under control is essential for all of us, but especially for the more than 37 million Americans living with type 2 diabetes. Typically, calorie-counting and strict adherence to a diet are recommended as methods to manage weight and keep critical numbers in check for people with the disease, along with medications and other medical interventions when indicated.

But calorie-counting takes a lot of effort and discipline. Meanwhile, intermittent fasting has been shown to have some weight loss and health benefits similar to, and at times even more powerful than, calorie restriction. Now, a study published October 27, 2023 in the Journal of the American Medical Association (JAMA), reinforces that.

The study was led by a team of medical doctors, doctorate-level researchers, and dietetics clinicians at the University of Chicago. The research team aimed to see if intermittent fasting could be more successful for weight loss and blood sugar than a calorie-restricted diet for people with type 2 diabetes—though it may offer more universal applications for non-diabetics, as well.

In the study, intermittent fasting beat out calorie restriction for weight loss and blood sugar maintenance

The study examined data from 75 participants between the ages of 18 and 80 years, all with type 2 diabetes and who were overweight. The participants were randomly assigned to one of three categories to follow one of three designated eating plans for six months:

  • The first group would follow an intermittent fasting plan, observing an eight-hour window to eat—specifically, between noon and 8:00 p.m.
  • the second group would reduce their calorie intake by 25%
  • and the third was to maintain their current diet plan.

Intermittent fasting between noon and 8:00 p.m. resulted in the the most significant weight loss, with some participants in this group losing up to 6% of their body weight. For a 180-pound individual, that equates to a weight-loss difference of 11 pounds. (The average among this group landed at a nearly 4% weight loss rate.)

Meanwhile, those who simply reduced calories were only able to maintain an average less than 2% weight loss. It’s also interesting to note that those who fasted reduced their calorie count by around 300 calories per day on average, which means they cut 100 calories more than those who were trying to reduce calories. Again, this was without trying to limit what they ate.

An exciting part of the study is that the type of intermittent fasting that was studied equated to the participants simply enjoying lunch and dinner without dictating which foods they could or couldn’t eat. The study authors state that this finding aligned with prior research which had shown with intermittent fasting, people tend to reduce daily calories by 200 to 500 without consciously counting them.

Fasting was also shown to be as beneficial for HbA1c levels and glucose management as traditional dieting—the researchers report: “Levels of HbA1c decreased in the [time-restricted eating] … and [calorie restriction] … groups, relative to controls, with no differences between [these] groups.”

Another interesting point is that on average, the fasting group was only able to adhere to the time-restricted eating plan for an average of six days per week, according to the data, which may suggest there’s some wiggle room for cheat days. 

Said the study’s lead author Krista Varady, PhD, of the Department of Kinesiology and Nutrition, University of Illinois Chicago: “Our study shows that time-restricted eating might be an effective alternative to traditional dieting for people who can’t do the traditional diet or are burned out on it.” Dr. Varady added: “For many people trying to lose weight, counting time is easier than counting calories.”

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How to try intermittent fasting for weight loss 

To lose weight with intermittent fasting, you don’t have to be a diagnosed type 2 diabetic—though anyone, including diabetic patients, should consult with a healthcare professional before making a change to your diet or eating habits. Once a licensed healthcare professional has cleared you, familiarize yourself with various intermittent fasting schedules.

The participants in this study followed a 16:8 plan, or time-restricted eating, which is eating for eight hours and then fasting for 16. There are other variations of this method, such as a 14:10 or 20:4. Typically, sources suggest people find it easiest to spend some of the fasting time sleeping.