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Why exercise alone may not help you lose weight

If you're working on your weight (or even if you're not), chances are you've been told to "eat less and exercise more."

Those who follow this advice often find themselves frustrated and not losing as much weight as they had expected, given the number of calories they had burned. Often the explanation for this is that "muscle weighs more than fat."

While this is true in the sense that the same volume of human muscle weighs about 20% more than the same volume of human fat (think a cube the same size for each), the truth seems to be rather more boring than metaphorically turning muscle to fat.

Researchers at Louisiana State University in Baton Rouge, Louisiana designed a study to see if those who exercised more frequently as part of their usual routine, before joining an exercise-focused weight loss program, would lose more or less weight than their peers who habitually exercised less frequently (Obesity 2020(28); 882-892).

Over 100 men and women (average age about 49 years, average Body Mass Index 31, or clinically obese) participated in their controlled trial. Each participant was randomly assigned to one of three groups, which as appropriate provided structured exercise classes for the participants:

1. A moderate exercise group, with the goal of burning at least 8 calories per kilogram of body weight per week, or at least 725 calories per week for a person weighing 200 pounds;
2. A high-dose exercise group, with the goal of burning 20 calories per kilogram of body weight per week, or 1814 calories per week for a person weighing 200 pounds; or
3. A control group of those who did not customarily exercise and were not directed to change their level of exercise.

The participants participated in the group exercise classes (or not, according to their randomization) for 24 weeks. At the start and end of the study the participants had their overall body fat measured using a bioimpedance scale and their waist and hip measurements taken by trained professionals. Their actual energy intake (the number of calories they consumed) and expenditures (the number of calories they burned) were measured on multiple occasions using the gold standard of doubly-labeled water.

Regardless of which group they were assigned to, the participants kept track of their food intake and wore highly sensitive motion-sensing armbands to estimate the number of steps they took each day as well as how much they moved overall.

You might expect that those who were not used to exercising frequently or intensely would lose more weight than those participants who were more used to frequent exercise. After all, they're suddenly burning far more calories than they're used to, right?

You'd be wrong.

The authors found that those who usually excercised less frequently or intensively lost less weight than those of their peers who were more accustomed to regular exercise.

It seems, from the data gathered regarding each participant's caloric intake, that those who were not used to regular, intensive exercise were more likely to increase their caloric consumption (that is, to eat more) once they started a more intense exercise program than those who were already used to regular exercise.

What this means for you

If you've started an exercise regime but are disappointed in how little weight you have lost, you might want to take a look at what you're eating. It's normal to be hungrier when you burn more calories, but if you're working on your weight that is a reason to be careful. If you are hungry after a workout, have a palmful of plain or dry roasted nuts or a piece of fruit as a snack. They'll help keep you satisfied, you'll improve your Mediterranean Diet score, and you'll likely tide yourself over until your next meal without consuming too many extra calories.

First posted: September 30, 2020