You'd have to look really hard to find a fitness coach, trainer, or dietitian that didn't "know" that cutting food intake by 3500 calories results in a one-pound loss. Cut 500 calories a day and after a year you'll have lost 52 pounds, right?
It's easy to find confirmation of that fact, too. It's estimated that at least 35,000 educational weight loss sites and probably a 100,000 more fitness sites make mention of the 3500-calorie rule.
Unfortunately, it turns out that the rule is a particularly good example of what Mark Twain meant when he wrote, "A lie can travel halfway around the world while the truth is putting on its shoes."
Only in this case, the lie has traveled around the world for the last 61 years or so while truth has been shacked up in a cheap hotel room with some floozy from Fresno and 1,000 cases of Thunderbird and can't even find its shoes, let alone put them on.
To be fair, the 3500-calorie rule wasn't intended to be a lie, but it is completely false. It originated from researcher Max Wishnofsky, who, in 1958, burned a pound of fat in a calorimeter and saw that it gave up about 3500 kilocalorie's worth of energy.
And we all swallowed it, hook, line, and pork rind, without realizing that weight loss is governed by an altogether different mathematical formula and doesn't continue in a linear fashion.
It took a mathematician by the name of Kevin Hall, Ph.D., to figure out that over the course of the first year of a diet, people only lose about half of what's predicted. In effect, the true number of calories it takes to burn a pound of fat is closer to 7,000.
Before you scream in anger and frustration, consider what Hall said: "I suppose some people will be bummed out, but we believe it's better to have an accurate assessment of what you might lose. That way you don't feel like a failure if you don't reach your goal."
The main problem with the 3500-calorie rule was it failed to take into consideration that the body pivots and adapts in a number of ways to minimize or even erase the effects of reduced caloric intake. It doesn't account for gender, either, or the fact that the metabolic rate drops as body weight decreases.
These observations go a long way in explaining the oft-heard complaint that "losing the last 5 pounds is the hardest."
Hall and his colleagues have put together a more accurate weight-loss predictor called the Body Weight Simulator, but truth be told, it's probably best used by people who have significant amounts of weight to lose and who expect to be in calorie-restriction for 6 months to a year or more.
But what about the average reader of this site who probably, at most, needs to lose the occasional 10 pounds to get ready for summer? For them, the old 3500-calorie rule probably holds true for at least the first few weeks of dieting, but that's when the formula starts to falter. Cutting out 500 calories a day no longer remains reliable or viable.
Adjustments will have to be made in order for weight loss to continue. Additional calories will have to be slashed and exercise intensity or duration will have to be increased. Protein to carb to fat ratios might have to be reassessed and adjusted.
But rather than gnash our teeth over this new, 7000-calorie formula, we should, as Hall said, be happy to have a more accurate assessment of what me might lose. I think its greatest benefit, though, will come for those of you who train overweight people or give them nutritional advice.
If clients know what to realistically expect, they likely won't get as frustrated when their weight loss fails to measure up to what you and the now defunct 3500-calorie rule promised them.
- Hall KD et al. Energy balance and its components: implications for body weight regulation. Am J Clin Nutr. 2012 Apr;95(4):989-994. PubMed.
- Webb D. Farewell to the 3500-Calorie Rule. Today's Dietitian. 26(11):36.