• Posted April 19, 2024

Calories, Not Meal Timing, Key to Weight Loss: Study

A head-to-head trial of obese, pre-diabetic people who ate the same amount of daily calories -- with one group following a fasting schedule and the other eating freely -- found no difference in weight loss or other health indicators.

So, despite the fact that fasting diets are all the rage, if you simply cut your daily caloric intake, weight loss will occur no matter when you eat, the study authors concluded.

"Consuming most calories earlier in the day during 10-hour time-restricted eating did not decrease weight more than consuming them later in the day," wrote a team led by Dr. Nisa Maruthur, an associate professor of medicine at Johns Hopkins Medicine in Baltimore.

Her team presented its findings Friday at the annual meeting of the American College of Physicians (ACP) in Boston. The study was published simultaneously in the Annals of Internal Medicine.

Intermittent fasting has become very popular among weight-conscious Americans in recent years.

In an ACP news release, the researchers noted that "evidence shows that when adults with obesity limit their eating window to 4 to 10 hours, they naturally reduce caloric intake by approximately 200-550 calories per day and lose weight over 2-12 months."

But what if people simply cut their daily calories by the same amount, without shifting their eating schedules?

The new trial involved 41 people with obesity and pre-diabetes, mostly Black women averaging 59 years of age.

Participants were assigned to one of two eating regimens.

Twenty-one of them engaged in time-restricted eating, where they ate only between the hours of 8 a.m. to 6 p.m. and consumed most of their calories before 1 p.m. 

The other 20 participants ate in more regular pattern, eating anytime between 8 a.m. and midnight and taking in most of their daily calories after 5 p.m.

However, all of the participants "received prepared meals with identical macronutrient and micronutrient compositions" and identical daily calorie counts.

The bottom line: After 12 weeks, there was no significant difference in weight loss between the two groups, the Hopkins researchers found.

Folks on the fasting regimen lost an average of just over 5 pounds, while folks who ate on a regular schedule lost a bit more, about 5.7 pounds.

The team also saw no significant difference in blood sugar changes between the two groups.

Their conclusion: Obese, pre-diabetic people may lose just as much weight by cutting daily calories without adhering to a fasting diet that cuts calories by the same amount.

Drs. Krista Varady and Vanessa Oddo, nutrition researchers at the University of Illinois, wrote an editorial accompanying the new study.

They applauded the new research, but believe there are still good reasons for overweight folks to try fasting regimens.

"The rising popularity of time-restricted eating is most likely due to its sheer simplicity -- it does not require a person to count calories to lose weight," they pointed out.

The Hopkins study shows that a fasting diet is "effective for weight loss, simply because it helps people eat less," they said.

So, if you find it a hassle to constantly track your calories each day, a fasting diet could still be right for you, since fasting naturally reduces calories to levels that can trigger weight loss, Varady and Oddo reasoned.

"Although time-restricted eating is no more effective than other diet interventions for weight reduction, it offers patients a simplified approach to treating obesity by omitting the need for calorie counting," they concluded.

More information

Find out more about intermittent fasting at Mass General Brigham.

SOURCES: American College of Physicians, news release, April 19, 2024; Annals of Internal Medicine, April 19, 2024