The reason that severe low calorie diets don’t work is due to the science behind Resting Metabolic Rate or RMR. RMR is the calories that our body burns at rest. This includes bodily functions like digestion, breathing and blood circulation. Your body is hard at work even when you’re not moving. However, just like anything else in life, not everyone has the same RMR. Sex, body size, body composition and age all impact how many calories you burn. Men typically have less body fat than females and therefore burn more calories. Larger individuals burn more calories than smaller individuals and those with higher muscle mass have higher caloric burn. Caloric burn also slows as you age.
When we eat too few of calories or go on a diet that provides our body with less calories than our RMR, the body has to compensate to find energy. This is called starvation or semi-starvation mode. During this mode the body’s survival instincts kick in. Muscle gets broken down and used as fuel and the body’s metabolism slows to conserve energy. This means fewer calories burned and a decrease in muscle mass. Studies have shown that 2 weeks of a starvation diet can drop an individual’s RMR by almost 15%. This slow metabolism and breakdown of muscle can actually cause weight gain. To make matters worse, weight loss attributed to this starvation is typically not permanent.
Overall, even though it sounds counterproductive, you must fuel your body at its current state in order to lose weight. A slight deficit in calories (~250-500calories/d) will help the body stay out of starvation mode and burn excess fat for weight loss. The majority of us should not be eating less than 1200 calories per day unless under the supervision of a physician or registered dietitian. Predictive equations like the Mifflin St. Jeor equation and Harris Benedict equation can be used to estimate RMR. RMR breathing tests are also offered at many hospitals and gyms. Knowing this information can help you determine the best approach to losing weight based on the your body’s caloric needs. Even if you don’t like to count calories, focusing on your body cues for hunger and fullness can typically ensure that you are meeting your caloric needs.
Say goodbye to your lemonade cleanse 6 times per day and bring back the fruits, vegetables, lean protein and whole grains. Let’s get on board and start losing weight by eating more!
Mahan, L., Stump, S., Raymond, J., Krause, M. (2012). Krause’s food & nutrition care process. St. Louis, Mo. Elsevier/Saunders.
Mayo Clinic. Metabolism and weight loss: how you burn calories. www.mayoclinic.com/health/metabolism/WT00006#. August 15, 2014.
Nutrition 411. Metabolism: A Look at the Facts. http://www.nutrition411.com/patient-education-materials/weight-control/item/1065-metabolism-a-look-at-the-facts/. August 15, 2014.