How the Types of Calories You Eat Might Affect Your Weight

Weight loss efforts might be more successful with reduced fat calories than with reduced carbohydrates

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) A calorie is a calorie, right? Not so fast.

When obese men and women are on strictly controlled diets, cutting the fat in the diet may be more effective for weight loss than cutting carbs, a new study found.

This study was small and the patients very closely monitored. The study authors found that people lost much more body fat when their intake of dietary fat was restricted compared to when carbohydrates were restricted.

“Calorie for calorie, reducing dietary fat results in more body fat loss than reducing dietary carbohydrate when men and women with obesity have their food intake strictly controlled,” said lead study author Kevin D. Hall, PhD, of the National Institute of Diabetes and Digestive and Kidney Diseases, in a press release. “Ours is the first study to investigate whether the same degree of calorie reduction, either through restricting only fat or restricting only carbohydrate, leads to differing amounts of body fat loss in men and women with obesity.”

Dietary recommendations for people who are obese vary greatly. Almost all agree that people who want to lose weight should decrease their calories and exercise. Dr. Barry Sears, an expert in inflammatory nutrition, told dailyRx News that obese patients should also be sure to get enough protein.

"What is needed for effective fat loss (which is different than weight loss) is a calorie-restricted diet with a protein-adequate diet (to prevent loss of muscle mass) with decreased levels of both carbohydrates and fat," Dr. Sears said.

In this study, the question was whether the type of calories eaten mattered in losing body fat. Nine women and 10 men participated. The average age of the patients was 24.

Dr. Hall and team used body mass index (BMI) as a measure of obesity. BMI is a measure of body fat based on height and weight. A normal BMI ranges from around 18 to 25. The study patients’ average BMI was 36.

Dr. Hall and team began this study by putting the subjects in a controlled ward where they lived for 24 hours a day. These researchers monitored food intake and activity very closely.

Subjects ate a diet of 50 percent carbohydrates, 35 percent fat and 15 percent protein. Calories differed, but for five days, each person was fed just enough to maintain his or her body weight.

On the sixth day, the subjects were split into two groups. Each group got 30 percent fewer calories, but in one group, fat calories were reduced. In the other group, carbohydrate calories were reduced.

These patients ate about 800 fewer calories each day. Dr. Hall and team measured how much fat each person burned and how much fat they ate.

Dr. Hall’s team then discharged the test subjects, who spent two to four weeks eating what they wanted to. At the end of this “washout” period, the study patients were readmitted. This time, they were switched to the opposite diet from the one they first ate.

Dr. Hall and colleagues found that when fat calories were restricted, study patients lost 67 percent more fat than when carbohydrates were restricted.

This study was presented March 5 at ENDO 2015, the annual Endocrine Society meeting, in San Diego.

The Intramural Research Program of the National Institute of Diabetes and Digestive and Kidney Diseases funded this research. Dr. Hall and team disclosed no conflicts of interest.

Review Date: 
March 7, 2015
Last Updated:
March 16, 2015