Bodybuilders have long known that if you eat too little for too long, you can actually decrease your resting metabolic rate (the number of calories you burn at rest).
Now, scientists are catching up to what our muscle-building friends have known in the real world for a long time. Researchers from the Pennington Biomedical Research Center in Louisana studied long term dieting in 48 normal-weight subjects.
Obesity 15:2964-2973 (2007) Effect of Calorie Restriction on Resting Metabolic Rate and Spontaneous Physical Activity
One group of subjects reduced their calories below normal by 25% for 6 months. A second group reduced their calories by 12.5% and exercised to burn another 12.5% of calorie intake each day. A third group consumed only 890 calories per day until they lost 15% of their body weight, and the fourth group served as a control group.
Researchers found that resting metabolic rate decreased in subjects on the 25% calorie restriction group after only 3 months. Likewise, this decrease in metabolism was also found in the 890 calorie per day and the exercise + diet groups, but not until after 6 months.
In addition, researchers also found that the calorie restriction subjects decreased the amount of physical activity they did each day.
Therefore, when you diet too hard, too much, and too long, your body starts to conserve energy by reducing your metabolism and by decreasing the amount of activity you do.
To avoid lowering your metabolism...
1) Don't cut your calories by such a big number. Instead of cutting by 25%, cut only by 10%.
2) Permit yourself a reward meal each week where you eat your favorite foods and a normal number of calories for the day.
3) Take a few days off dieting every 8-10 weeks, where you go back to eating a normal number of calories each day.
These three simple changes should help you lose weight while avoiding a reduced metabolism. Of course, you should also follow an exercise program to keep up your activity levels.
Eat right to lose weight,
Craig Ballantyne, CSCS, MS