If you’ve ever looked up information on weight loss, you have no doubt come across the commonly cited rule that cutting 500 calories a day will lead to a loss of one pound each week (a pound equals 3,500 calories). But if you’ve ever tried to put this maxim into effect, you may have found that your weight loss did not progress as smoothly as you’d hoped or expected. Now, in a new report in The Lancet, researchers from the National Institute of Diabetes and Digestive and Kidney Diseases have explained why real-life weight loss takes longer than the “3,500-calorie rule” would allow.
What this rule fails to take into account, the researchers note, is the body’s dynamic response to changes in diet and body composition. When someone gains weight, for instance, his baseline energy requirements increase in order to maintain the extra body tissue and to move it around. Likewise, when he loses weight, these energy needs decrease. So if a person decreases his calorie intake below his baseline energy requirements and begins to lose weight, his energy needs will also decrease, and he will eventually stop losing weight.
According to the researchers, “This ubiquitous weight-loss rule (also known as the 3,500 [calorie]-per-pound rule) was derived by estimation of the energy content of weight lost, but it ignores dynamic physiological adaptations to altered body weight that lead to changes of both the resting metabolic rate as well as the energy cost of physical activity.” This article further notes that “If a 300-pound dieter could really lose a pound a week by cutting his regular diet by 500 calories, he would vanish entirely in six years.”
A more realistic scenario, states researcher Kevin D. Hall, PhD, is that cutting 500 calories a day would lead to a 50-pound weight loss over three or more years. And even in this case, the calorie reduction would need to be maintained for the duration of that time.
Dr. Hall and colleagues created what they feel is a more accurate model of weight loss that incorporates mechanisms to reflect the body’s dynamic response to changing body weight and diet. Using this formula, they determined that each reduction of 24 calories daily eventually leads to the loss of 2.2 pounds of weight, but only half of this loss occurs in the first year of reduced calorie intake. In three years, 95% of that weight loss will have been achieved. According to this piece in The New York Times, the model suggests that weight-loss plans might best be achieved in two parts: “a temporary, more aggressive change in behavior at first, followed by a second phase of a more relaxed but permanent behavioral change.”
Trying to lose weight according to the old rule, Dr. Hall noted, could lead to discouraging results.
To learn more about the report, read the article “Weight Loss Through Cutting Calories Less Than Expected” or see the report’s abstract in The Lancet. And for more reasons you might not be losing weight as quickly as you’d expected, check out the article “Why Can’t I Lose Weight: Finding Your Trouble Spots,” by diabetes educator and registered dietitian Jacquie Craig.