Introduction

It has commonly been stated almost everywhere on the web, in print magazines, by fitness coaches and dieticians, that in order to lose 1 lb of fat per week, you need to burn 500 calories a day.

In other words, according to many, it requires a caloric deficit of 3500 kcal to lose 1 pound of fat.

Do that consistently every week, and you'll lose 1 lb of fat per week.

Right?

Not entirely... and let's find out what the flaws are.

History of the 3500-calorie rule

In the 1950's, it was concluded that to lose or gain a pound of body weight, the energy equivalence of 3500 calories needs to be in deficit or in surplus, respectively.

In other words, a surplus or deficit of 3500 calories from your caloric maintenance level results in a gain or loss of 1 pound of body weight, respectively.

This conclusion has since been very popular and adhered to by many fitness enthusiast, dieticians, researchers, papers, websites, blogs, articles, and magazines.

Over the years, however, additional research has shown that the above conclusion is not definite and needs lots of nuance.

How the 3500-calorie rule works

You can initiate weight loss by reducing your energy intake or increase your energy expenditure, or energy output, through exercise or a more active lifestyle.

To predict how much weight you’ll lose over a period of time, all you then need to do is to multiply the number of days with the absolute value of the energy deficit, and divide that result by 3500 kcal/lb.

For example, suppose you're in a 250 kcal energy deficit (meaning you eat 250 kcal less than what your maintenance level calories are) for a duration of 10 days.

Then your weight loss over those 10 days is (250 * 10) / 3500 = 0.71 lbs.

According to the 3500-rule, you can calculate longer periods.

The same 250 kcal deficit from the previous example but over a period of 180 days, for instance, will result in a weight loss of 12.86 lbs.

Flaws of the 3500-calorie rule

The problem with using the 3500-rule as a definitive formula to calculate weight loss, is that several assumptions are made which aren't accounted for in real life.

These assumptions are:

1. The energy intake for the individual does not change over time.
2. Energy expenditure or output does not influence weight loss.
3. Fat is the only substance that is lost or reduced during loss of body weight while on a low calorie diet.
4. Weight loss will continue to occur at a rate of 3500 kcal deficit per pound during the whole weight loss journey.

How the weight loss process works

Weight loss can be divided into two phases.

First phase of weight loss process

Initially, weight loss occurs more due to loss of carbohydrates and protein and less due to fat being burned during the process.

You'll also lose relatively lots of water during the weight loss process, because not only are the carbohydrates and protein molecules you will burn during weight loss associated with water molecules, your sodium intake will likely change as well, resulting in changes in your body's fluid balances overall.

The result of the above is that weight loss in the initial phase does not equal a loss of 1 pound of fat for each 3500 kcals burned.

In fact, the energy content of weight change (whether you're trying to lose or gain weight) is far less than 3500 calories per pound and also not constant.

In other words and in relation to weight loss, reducing your caloric intake to a deficit of 3500 calories per week overestimates the weight loss in fat.

Second phase of weight loss process

In the second phase of the weight loss process, things will slow down and it becomes harder to maintain the same rate of weight loss as during the initial phase.

This is because the energy content of weight change is not constant at 3500 kcal/lb; it's much lower than 3500 kcal during the first phase, but approaches the 3500-rule in the second phase.

Also, as your body adapts to being in a caloric deficit, your resting energy expenditure and other metabolic processes get reduced as well.

The result of all of the above is that weight loss will slowly decrease in this second phase of the weight loss journey. This makes a linear formula such as the 3500-rule inaccurate.

Is the 3500-rule useless?

If you plot a graph that shows the weight loss over time, the 3500-rule applied to the graph will result in a straight line with body weight decrease at a linear rate over the course of time.

However, as multiple studies have shown, in reality the weight loss graph looks more like a reciprocal function.

So, if the 3500-rule is so inaccurate, does it have any use then?

If you ask me, despite that the 3500-rule isn't accurate as we've seen above and greatly overestimates the results you can achieve by adhering to that rule... in general, I'd say the 3500-rule is a great guide to use for the general public for losing weight.

The 3500-rule and beginners

The thing is, the rule provides a handle for people to make simple calculations. If you're goal is weight loss, then the most important thing is to take the first step and actually do something about you being overweight.

It doesn't help to show a beginner who'se looking to lose weight all kinds of difficult calculations and get into micro-details about diet, exercise, vitamins and minerals, supplements, periodization, progressive overloading, supersets, drop sets, etc. etc.

That all comes naturally as one gains more experience and knowledge in the weight loss process and in his/her fitness journey in general, over the course of time.

In my opinion, making it as easy for beginners to start their weight loss journey should be a priority, so they have the least amount of hurdles to overcome initially (assuming that individuals do it all by themselves with nothing but info found on the internet; if you have a personal trainer then hopefully he/she figures everything out for you and uses the accurate models for weight loss predictions instead of the 3500-rule).

And for that, the 3500-rule will do.

The 3500-rule and intermediate fitness enthusiasts

Now, if you're an advanced fitness enthusiast or have previous experience with weight loss and muscle gain, by all means (and you probably should know better, assuming you've read up a bit on fitness and nutrition during your own fitness journey) use more accurate methods than the 3500-calories rule to calculate your fat loss or gain during your cutting phase or bulking phase, respectively.

If you've gained a few unwanted pounds yet have experience with strength training in general, consider using the following calculator: Weight loss predictor.

My own experience with the 3500-calorie rule

As a matter of fact, in my own fitness journey when I experimented with gaining (muscle mass) and losing (fat loss) weight, I accidentally discovered the flaws in the 3500-rule myself.

By that time, I didn't even knew there were flaws in the theory of burning 3500 calories to lose 1 pound of fat per week...

What I noticed, was that the weight measured on the scale each week did not accurately correspond to the calculations based on the 3500-rule after a few weeks.

It became harder and harder to keep losing 1 pound of fat week by week as I progressed in my fat loss journey, and that was due to the fact that my body's resting metabolic rate slowly decreased as I continued staying in a caloric deficit over time, meaning I had to eat even less to maintain the weight loss progress.

As soon as I noticed my weight loss didn't progress on the scale for a period of multiple weeks to months, I started readjusting my caloric intake by slowly reducing the calories.

This resulted in the weight to drop again slowly and bit by bit.

It turned out: the 3500-rule that I used to calculate how much weight I'll lose over a set period of time wasn't that accurate, as I've described in this article.

And that's how I figured out by my own experience, that the 3500-rule has its own flaws.

Conclusion

Personally, I think the 3500-calorie rule is a great general rule for absolute beginners to begin their weight loss (or gain!) journey if they don’t have access to a personal trainer or plenty of time to do all the research by themselves.

For beginners, I think the 3500-rule is a decent tool for beginners to get arough estimate of their predicted body weight after a period of dieting and exercising, but they should know and be aware of its flaws, though.

For the more advanced gym goers or people wanting to get better predictions for their weight change, it's essential to note that this rule is a simplification and has been criticized for oversimplifying the complexities of weight loss. The human body is dynamic and adapts to changes in caloric intake and expenditure. Factors such as metabolism, body composition, and hormonal changes can influence weight loss and make it more complex than a simple linear equation.

What do you think of the 3500-rule? Do you use it? And if so, were you aware of its flaws?