If you burn 3,500 calories, you lose one pound, right?
"I see dietitians using it all the time, making recommendations based off of it," said Kevin Hall, who is a researcher at the National Institute of Diabetes and Digestive and Kidney Diseases. "Unfortunately it's completely wrong."
The adage dates back to the 1950s, when medical researcher Max Wishnofsky measured how much energy a pound of fat tissue represents, and found that it was 3,500 kilocalories, otherwise known as calories. Theoretically, he had calculated how many calories a person had to burn—or forego—in order to lose a pound of fat. But Wishnofsky made a couple spurious assumptions.
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The much bigger mistake Wishnofsky made was misunderstanding how our bodies react to weight loss. As soon as we start cutting calories from our diet, the number of calories our body expends begins to fall. "It literally starts happening on the first day," said Hall. "And it continues to mount as you lose weight."
The reason Wishnofsky, and so many others since, have botched this biological fact is that it's fairly counterintuitive. The tendency is to assume that as you lose weight, the same calorie cut back should prove even more effective once you are lighter, and, presumably, in need of less food. At the very least, it should continue to produce the same results as it was when you were heavier. So cut 500 calories per day, and drag it out for a week, and you'll be roughly one pound lighter; double the decrease, and you'll drop two pounds; triple it, and do away with three.
Those adjustments mean that the more weight you lose, the harder it is to keep losing weight:
"Over time, the more weight you lose, the more your metabolic rate drops," explained John Peters, a leading researcher at the Anschutz Health and Wellness Center at the University of Colorado. "In order to keep losing weight at the rate you started losing weight, you’re going to have to eat even fewer calories. A month in, you might have to eat another hundred fewer; a month after that you might have to drop it another hundred."
Hall has, in many ways, spearheaded the movement to shed the nutrition world of the 3,500 calorie rule. In 2011, he created a model, called the Body Weight Planner, that directly challenged the adage. Drawing from a vast pool of data, the tool approximated metabolic changes in people trying to lose weight, and showed how greatly the 3,500 calorie rule overestimates weight loss.
That basic misunderstanding leads to frustration when our bodies actually fight against our efforts to lose weight. The gap between what we think we should be losing and what actually occurs can often be devastating psychologically. It could be the main reason why most diets end up with the dieter at the same weight (or greater) within a year.
