You know the formula. To lose a pound of body fat you have to reduce your calorie intake by 3,500 calories since that’s how many calories are equal to a pound of fat. For years dieticians, nutritionists and doctors have stood by this formula. But researchers at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) are now saying this formula is flawed. Why? Because it fails to take into account that metabolism slows as you lose not only body fat but metabolically active muscle.
What are calories?
Calories are the energy in the food you eat. The human body needs energy in order to function and repair itself; your body converts the calories it obtains from food into energy. However, if you consume more calories than your body needs, the calories are stored in your body as fat. In order to lose weight, you need to use up these fat stores.
The average grown woman needs 2,000 calories a day in order to function properly, while the average grown man needs 2,500 calories. Consuming more than this will lead to weight gain; consuming less will lead to weight loss.
3,500 calories is equivalent to one pound of weight. So, if you cut 3,500 calories from your diet, you will lose approximately 1lb in weight. If you consume an extra 3,500 calories, you will gain 1lb.
When 3,500 Calories Doesn’t Equal a Pound
According to the formula, you’ll lose a pound each week if you cut back your food intake by 500 calories a day (500 x 7 = 3,500 calories). Sounds simple enough, but researchers at NIDDK argue that the rate of weight loss is going to be slower for the average person due to adjustments the body makes for the lost body weight and muscle mass. As you lose weight, you require less calories and metabolism slows down to compensate.
NIDDK researchers think this formula sets up unrealistic expectations that not all dieters are going to be able to meet. When they don’t see the pound-a-week weight loss, they become discouraged and give up. They point out that weight loss isn’t usually as rapid as the current formula predicts and sets people up for unrealistic expectations and failure. What people fail to realize is that as they lose weight their BMR will also decrease which means they’re burning less calories each day than what they thought they were.
The Problem of Set-Point
Are they on the right track? It’s true that the current formula doesn’t take into account adjustments your body makes when you try to lose weight. There’s a theory that the body has a genetically determined set-point that it tries to maintain and when you try to go below that set-point, it makes compensations like a slow-down in metabolism that makes it harder to shed more weight. When you first start restricting calories, especially if you go on a low-carbohydrate diet, weight loss may be rapid, but some of the lost weight is water. Weight loss usually slows after that. As you try to go below your set-point, it slows even more. This is why you have to be careful when dieting. If you cut back too much your body will compensate by slowing down your metabolism.
Is Exercise the Answer?
One way to deal with the set-point challenge and the drop in metabolism that comes with weight loss is to do high-intensity exercise and strength training. These help to boost lean body mass, which speeds up metabolism and creates the right hormonal environment for continued fat loss. Trying to lose weight without the benefits of exercise is almost always more challenging.
If you’re trying to lose weight you should try to create a calorie deficit each day of 500 calories. This means you will be burning 500 calories more each day than you’re consuming. This calorie deficit should be created by a two pronged approach of both diet and exercise to help reduce the chances of your metabolism slowing down.
The Bottom Line?
Weight loss may not always be as simple as cutting back by 500 calories to lose a pound a week, but you can make it easier for yourself by adding high-intensity exercise and strength training to your weight loss plan. It’ll help you maintain a more favorable body composition too.
Medscape.com. “Better Way to Predict Weight Loss?”
International Journal of Obesity (2007) 31, 204-212.
Int J Obes (Lond). 2007 Feb;31(2):204-12.