Human metabolism cannot be reduced to a math problem from 1958. We’ve learned a lot since then.

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On Nutrition

The idea that you have to cut 3,500 calories to lose a pound was debunked several years ago — or so I thought. I expect patients to ask “How many calories do I need to eat to lose weight?” What I didn’t expect was a pre-eminent medical journal to not just perpetuate the calorie myth, but to try to persuade doctors to do it, too.

Earlier this year, the Journal of the American Medical Association (JAMA) published a viewpoint titled “Counting Calories as an Approach to Achieve Weight Control.” It came across my radar recently when I spotted a heavily promoted blog post written by a media doctor for the Calorie Control Council, a trade group representing the diet-food industry — think artificial sweeteners and fat replacers. Some highlights from the JAMA article:

  • “If a patient reduces caloric ingestion by 500 calories per day for 7 days, she or he would lose about 1 lb of body weight per week, depending on a number of other factors.” The first part of that sentence is wrong; see below for the “other factors.”
  • “While this is a simple arithmetic exercise, many patients find it overwhelming.” Human metabolism cannot be reduced to a math problem.
  • “Although counting calories is ideal, this may not be practical for many patients.” Calorie counting is not ideal, since research does not support its long-term effectiveness. As for “practical,” would you rather spend time counting calories, or living a life?

The idea that weight loss or gain is simply due to an imbalance between “calories in” and “calories out” is old-school thinking. The so-called 3,500-calorie rule — that creating a calorie deficit of 500 calories a day will result in one pound of weight loss per week — was developed in 1958. Today, we know that the human body is too complex to fit a simple math equation. In fact, research shows that weight loss or gain varies from person to person, even with the same calorie deficit. It also varies over time.

In one of his several published papers on the topic, researcher Kevin Hall, Ph.D., a metabolism expert and researcher at the National Institutes of Health, says the “3,500-calorie rule” ignores the sophisticated regulatory mechanisms our body has to adapt to changes in body weight, altering our basal metabolic rate (BMR) and how many calories we expend during physical activity, as well as orchestrating changes in our hunger hormone levels.

In fact, most people lose substantially less weight than the amount predicted by the 3,500-calorie rule, in part because weight loss slows with time. Even if on paper (or app) you are maintaining the requisite calorie deficit, your body has other ideas — effectively, it thinks you’re starving, and it’s trying to save you. The resulting adaptations contribute to plateaus during active weight loss and may make it harder for chronic yo-yo dieters to lose weight with each attempt.

To wit, a 2016 study of 14 competitors on NBC’s now-canceled “The Biggest Loser” found that the average BMR dropped by several hundred calories during competition, in spite of maintaining lean muscle through intense exercise. Six years later, only one competitor had kept off the weight; the rest regained 88 percent of the weight they lost, on average.

Despite regaining, their BMRs stayed low, which meant they required several hundred fewer calories per day to maintain their weight than they did when they were previously at that weight. In other words: Fervently chasing weight loss is a bit like grabbing a tiger by its tail.