Knowing how many calories are in a pound of fat can simplify weight loss in theory. If you know how many calories are in a pound and how many pounds you want to lose, you can wrap your head around what that will take for a calorie deficit over days or weeks.
If you ask most health professionals or look up how many calories to lose weight, the common answer is 3,500 calories.
In fact, over 35,000 educational websites site 3,500 calories in a pound of fat. This number also makes it convenient for weight loss; if you subtract 500 calories every day for a week that should equal to a pound of weight loss. 500 calories x 7 days = 3,500 calories lost in a week.
Though this principle is fairly simple, unfortunately weight loss does not always work this way.
There are many other unaccounted for factors that go into losing weight besides just using the 3,500 calories per pound of fat equation.
Where does 3,500 calories per pound come from?
The idea of 3,500 calories in a pound is thought to have originated from Dr. Max Wishnofsky in 1958. He estimated 1 pound of fat was about 3,500 calories, and from then on the idea continued (1).
The number 3,500 is based on 1 pound equaling about 454 grams. There are about 9 calories in a gram of fat, so 454 x 9 = 4,086 calories.
Why isn’t this the standard for calories in a pound of fat? Body fat is not purely fat; it also has a mixture of other liquids, cells and some proteins.
So, 3,500 takes into account that body fat is not purely fat.
Why 3,500 calories may not be fully accurate for weight loss
Using the 3,500 calorie estimate is an easy way to think about weight loss. We can wrap our heads around cutting about 500 calories a day, and we have many calorie and fitness apps that can help us track calories to meet our recommended target range for weight loss.
If someone wants to lose 10 pounds with losing a pound a week, it should take 10 weeks.
However, even if someone is carefully cutting back their food intake by 500 calories and/or exercising, weight loss may plateau throughout their program which can be frustrating.
This is where the 3,500 calories per pound of fat can lose some significance. Over time with weight loss, metabolism shifts. If your body size gets smaller, metabolic rate goes down.
Your body can become more efficient at burning calories.
Genetics play a role in determining metabolic rate, sleep patterns can interfere with weight loss and hormone levels also impact metabolism. The 3,500 calorie “rule” doesn’t take these factors into account during weight loss.
Also, with weight loss, it is normal to lose a combination of water weight, especially at the beginning of weight loss, along with fat loss. Sometimes lean mass is also lost. The calorie density in water weight and muscle mass is different than fat.
So what should you do instead of using the 3,500 calorie estimate?
Researchers are working on crating tools and weight loss equations that factor in changes for weight loss and during different states.
For example, the National Institute of Health under the guidance of Dr. Kevin Hall and other doctors (2) have created a Body Weight Simulator that takes into account different mathematical equations to factor in weight loss throughout different phases.
The Pennington Biomedical Research Center in Baton Rouge, Louisiana (3) also have a weight loss predictor equation available for anyone that has some cutting research taking more into account than just cutting 3,500 calories per week for weight loss.
The bottom line is that weight loss is not as linear as the 3,500 calorie model suggests. Weight loss can be an up and down process and may take longer than anticipated just from subtracting 500 calories per day.
Where does this leave us for weight loss?
In a given pound of fat on a human, 3,500 plus or minus some can still be an estimated amount for calories.
However, what we know now is that you can’t just simply subtract 3,500 calories and expect a pound of fat to come off.
Weight loss and metabolism regulation is more complicated than this. Genetics between people vary widely as well, not everyone will have the same response.
So where does this leave us for guidance for weight loss?
Using the 3,500 calories per week can still be an easy starting point for weight loss, just understand along weight loss journey it is not going to be a linear process. There are other factors you need to account for.
Also, calorie quantity is not the only thing that matters for weight loss. Calorie quality is just as important. We know the body does not handle all calories the same.
For example, 200 calories from soda is going to have a different effect on the body than 200 calories from an apple.
Focus on the nutrient density of your food along with the portion sizes. Focus also on the energy output side of the weight loss equation and building strength and muscular endurance with weight balance.