If you've ever counted calories to lose weight, you know that the number of calories per pound of fat is crucial information to know. And you've likely stumbled on this statistic more than once in your research: One pound of body fat is equal to approximately 3,500 calories.
In other words, if your goal is to, say, drop 1 pound of weight every week, it's as easy as burning 3,500 additional calories in your workouts over those seven days, or removing about 500 calories from your diet every day. Simple, right?
But despite how prevalent the statistic is, recent research shows that weight loss in the real world may not be quite that easy.
Where Did the 3,500 Number Come From?
According to an article in the July 2014 edition of The Journal of the Academy of Nutrition and Dietetics, the "rule" that 3,500 calories equals 1 pound first originated in 1958, when a doctor named Max Wishnofsky calculated that "the caloric equivalent of 1 pound of body weight lost" was 3,500 calories.
To arrive at this figure, the article explains, Wishnofsky drew on research that was available at the time, consulting studies where people had dropped weight on low-calorie diets. In these studies, participants were able to drop 0.6 pounds per day on average by eliminating 2,100 calories — so, using these numbers, Wishnofsky calculated that losing 1 full pound of fat meant eliminating 3,500 calories.
To confirm this, Wishnofsky studied the contents of 1 pound of human adipose (fat) tissue and found that each gram of tissue was 87 percent fat, while the rest was water and other non-fat solids. Because each gram of the tissue had 9.5 kcals, and 1 pound equaled 454 grams, Wishnofsky calculated that pure fat in a pound of tissue equaled about 3,500 calories — and so, losing fat was as simple as subtracting that amount from one's diet, Wishnofsky claimed.
Are There Really 3,500 Calories in a Pound?
Although the calculations make sense on paper, Wishnofsky failed to take a few things into account when it comes to actually losing fat in the real world.
First, losing weight doesn't necessarily mean losing fat, explains Tom Rifai, MD, clinical assistant professor at Wayne State University School of Medicine. "Particularly, when you cut carbs, the initial phase of weight loss means losing a bunch of water weight," he says.
And indeed, according to a study published in the December 2018 issue of Nutrients, people in the beginning phases of a diet lose not only fat but bodily fluids like water and skeletal muscle as well.
Second, the studies that Wishnofsky consulted to make his calculations were limited, conducted only in the short-term and using only women with obesity as subjects.
But people tend to lose weight at different rates depending on factors such as sex, initial body mass composition and the types of calories they're consuming — none of which Wishnofsky took into account when calculating how many calories it would take to lose weight. A woman who is obese and in the initial stage of weight loss, for example, will probably lose more weight at a quicker pace than would a slimmer woman, or someone who has been dieting for several months.
Furthermore, Dr. Rifai explains, weight loss is rarely linear. "When people lose weight, they eventually reach an equilibrium," he says. "Your muscle mass decreases, your metabolism drops and your body is carrying around less weight, so it's not working as hard and burning as many calories as it once was."
In order to continue losing weight and avoid a plateau, a dieter must adjust his or her caloric intake along the way, as well as adding in exercise and building up lean muscle to increase metabolism, per Harvard Health Publishing.
In other words, even though someone might lose a pound in the beginning of their diet by cutting out 3,500 calories, they may need to cut even more calories from their diet and incorporate other changes to lose pounds later on.
Can the 3,500 Rule Still Apply to Weight Loss?
All in all, the 3,500 rule isn't perfect. But fortunately, it's still a decent guideline to follow for people who want to lose weight.
"It's true that if you cut 500 calories from your daily diet, you're going to lose weight," Dr. Rifai says. But weight is only partly fat, so losing a pound of weight and losing a pound of fat are two different things, he adds.
To avoid shedding lean tissue and fluids rather than fat, the Mayo Clinic recommends a slow-and-steady rate of weight loss, which means no more than 1 to 2 pounds per week. That means, if you're using 3,500 as a guideline, you should aim to cut or burn a maximum of 7,000 calories every seven days.
And of course, as you progress on your weight-loss journey and your body composition changes, you may need to adjust your calorie deficit. That's where a calorie tracker like LIVESTRONG.com's MyPlate app can come in handy, to help you track what you're eating and burning and help you understand how that's affecting the scale, so you can tweak your numbers as needed.
"If you measure a pound of human fat, it's still going to be about 3,500 calories," Dr. Rifai summarizes. "But we understand the science behind weight loss a little better now, and burning a pound of human fat is a much different story."
- The Journal of the Academy of Nutrition and Dietetics: "Time to correctly predict the amount of weight loss with dieting."
- Nutrients: "Body Composition Changes in Weight Loss: Strategies and Supplementation for Maintaining Lean Body Mass, a Brief Review"
- Harvard Health Publishing: "The Truth About Metabolism"
- American Council on Exercise: "Body Composition: Which Numbers Matter?"
- National Institutes of Health: "NIH study finds cutting dietary fat reduces body fat more than cutting carbs"
- Mayo Clinic: "Why do doctors recommend a slow rate of weight loss? What's wrong with fast weight loss?"