Pure fat has a very high energy content, or about 9 calories per gram. This is about 4,100 calories per pound of pure fat. Body fat consists of fat cells, called adipocytes, which also contain fluid and protein.

Calories are the energy in food.

They fuel everything you do, from sleeping to running a marathon.

Calories can come from:

Your body can use calories to fuel work right away or store them for later use.

Some calories can be stored as glycogen (carbs), but the majority are stored as body fat.

• explains how many calories are in a pound of body fat
• discusses the 500-calorie-deficit myth
• presents some tools for predicting realistic weight loss

## What is body fat?

Let’s take a moment to define what we mean by body fat.

For starters, body fat is not just pure fat.

Pure fat has a very high energy content, or about 9 calories per gram. This amounts to about 4,100 calories per pound of pure fat.

However, body fat is not just pure fat. Body fat consists of fat cells, called adipocytes, which also contain fluid and protein in addition to fat.

Therefore, the calorie content of body fat is going to be a bit less than the calorie content of pure fat (1).

Summary

Body fat is mixed with fluid and protein. Therefore, its composition and calorie content are not the same as pure fat.

## Does one pound of body fat contain 3,500 calories?

In 1958, a scientist named Max Wishnofsky concluded that the caloric equivalent of one pound of body weight lost or gained was 3,500 calories (2).

He based his conclusion on the scientific evidence available at the time. Decades later, his result has been cited thousands of times by the media and in scientific literature (3, 4, 5, 6).

It’s basically become common knowledge that one pound of body fat contains 3,500 calories. But is it really true? Let’s try to find out.

We will be using generally accepted values for this calculation. However, some research does show slight variations (2).

In general, we can assume that:

• One pound equals 454 grams.
• Pure fat contains 9 calories per gram.
• Body fat tissue is 87% fat.

Using those values, we can conclude that a pound of body fat actually contains anywhere from 3,436 to 3,752 calories.

However, it is important to note that these calculations are based on old research.

Some of the studies state that body fat tissue contains only 72% fat. Different types of body fat may also contain varying amounts of fat (7).

Summary

A pound of body fat may contain anywhere between 3,436 and 3,752 calories, roughly estimated.

## The 500-calorie-deficit myth

It’s a common myth that if you eat 500 fewer calories each day, or 3,500 fewer calories a week, you will lose one pound of fat each week.

This would equal a total of 52 pounds in a year.

However, the reality is very different.

The 500-calorie-deficit myth significantly overestimates the potential weight loss that can be achieved over a period of time (8, 9, 10).

This estimate seems to work fairly well in the short term, for moderate weight loss in people who are overweight or who have obesity. But it falls apart in the long term and sets people up for failure and disappointment.

What this myth does not account for is the body’s response to the changes in body composition and diet (8).

When you reduce calorie intake, your body responds by making you burn fewer calories. You start moving around less, and the body becomes more efficient. It does the same amount of work, but it uses fewer calories than before (11).

You may also lose muscle mass along with the fat, which also makes you burn fewer calories.

This is often called starvation mode, although the technical term is “adaptive thermogenesis” (10).

Weight loss is not a linear process, and it typically slows down over time (12).

Summary

The 500-calorie-deficit diet overestimates the potential for weight loss. It does not account for changes in body composition and a reduction in calories burned.

## Better tools for predicting weight loss

Nowadays, there are apps and online tools that may provide a better, more realistic assessment of your predicted weight loss.

The Body Weight Planner, developed by the National Institutes of Health, provides calorie levels for both weight loss and maintenance.

It takes into account how diet and exercise contribute to weight loss, as well as how your body responds to reduced calorie intake. It has an immense number of mathematical calculations behind it (8).

Another good tool to predict weight loss is the Single Subject Weight Change Predictor, developed by the Pennington Biomedical Research Center.

This tool also allows you to calculate weight loss, based on dietary intake and exercise.

Summary

The 500-calorie-deficit rule is not a realistic way to predict weight loss. Better tools exist to predict weight loss over a period of time.

## Weight loss isn’t just fat loss

If you’re trying to lose weight, what you really want to get rid of is body fat — both under the skin and around the organs.

It’s important to remember that weight loss doesn’t necessarily equal fat loss. One unwelcome side effect of losing weight is the loss of muscle mass (13).

The good news is that there are some ways to minimize the loss of muscle mass.

You can:

• Lift weights. Studies show that resistance training can be incredibly helpful in preventing the loss of muscle mass when losing weight (14, 15, 16).
• Eat plenty of protein. With a high protein intake, your body is much less likely to break down your muscles for energy (17, 18, 19).

Both of these strategies are also useful to prevent a reduction in calories burned as you lose weight. Be sure to talk with a healthcare professional before adding these actions, because weightlifting and eating additional protein may not be right for everyone.

Summary

Weightlifting and high protein intake may help prevent muscle loss for people who are trying to lose weight. They can also help prevent a reduction in the number of calories you burn.

## Take home message

A pound of body fat may contain anywhere from 3,436 to 3,752 calories.

However, it is a myth that just eating 500 fewer calories per day (3,500 per week) causes weight loss of one pound.

This may work in the short term, but the body will soon adapt by making you burn fewer calories. For this reason, weight loss slows down over time.