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Calories and Metabolism

May 18, 2009

You know that to lose weight, you have to burn more calories than you consume. However, very low calorie diets (800-1,000 calories per day) often fail because not enough calories are being consumed to fuel physical activity. This leads to a decrease in metabolism. These restrictive diets are tough to maintain and also trigger the body to suppress the Resting Metabolic Rate (RMR) by about 20%. This is purely a survival mechanism to increase efficiency by burning less calories to do the same amount of work someone adequately fueled could do while burning more calories. Also, eating carbohydrates provides a “protein-sparing effect”. Those individuals that eat too few carbohydrates would need to use some protein for energy rather than for building and repairing muscles. This explains why high protein diets result in so much weight loss, you are losing LEAN BODY MASS!
Also, I am often asked about the decrease in metabolic rate with age. With each decade of life, RMR will drop 2-3%. This can be attributed to the loss of lean body mass due to physical inactivity. Fortunately, this loss can be minimized with regular resistance exercise.
I will also add that recent research is showing “fidgeters” burn an extra 150-300 calories per day. So maybe start playing with your hair or tapping your feet!
So what do you take from this?
  • Eat adequate complex carbohydrates (5-7 servings per day) for energy and adequate high quality protein (70 grams per day) for muscle repair.
  • Make sure to include weight resistance training in your exercise regimen.
  • Eat adequate calories for your activity level and stay above 1,200 calories per day.
  • Fidget a bit!
Emily Fonnesbeck RD,CD