The "500 Calorie Rule" states that "to lose one pound of body fat per week, an individual must eat 500 calories fewer per day than his or her body expends for 7 days. To gain one pound of body fat per week, the individual must eat 500 calories more per day for 7 days than his or her body expends."

According to conventional wisdom, for every 3500 kcal of excess energy accumulated, 1 lb of fat is stored in the body. A caloric deficit of approximately 3500 kcal produces a loss of 1 lb of fat, so if you are able to create a caloric deficit of 500 calories per day by decreasing how much you eat and increasing exercise, you will lose 1 lb a week.⁠

While technically true, this information can lead to dangerous advice. This statement implies that weight loss is linear. Hypothetically, if this were true, it would be possible to eventually lose so much weight that you weigh zero pounds, or eventually to continue losing weight you would have to be eating zero calories. Ridiculous. ⁠

Eventually, weight loss will slow or plateau. This happens because the less you weigh, the less calories your body needs to survive. If you weigh 140 lbs and you want to lose 10 lbs, and are able to maintain your weight by eating 2000 calories per day, following this wisdom, you would have to consume 1500 calories every day to lose 10 lbs in 10 weeks. If you then lose a lb a week, after 5 weeks you will weigh 135 lbs. But now, because you are smaller, your metabolism has decreased. You require less than 2000 calories to maintain your weight. Maybe now you can maintain at 1900. So if want to continue to lose weight at a rate of a lb a week, you would technically have to eat 1400 calories a day, not 1500.

BUT THE REALITY IS, most people don’t think of that. They will continue to eat 1500 kcals a day and wonder why they’re not losing weight as quickly. If they figure out they need to cut their calories more, they can end up on a dangerous cycle of eating less and less. THEN, because the body is fighting to be more efficient, it will figure out how to operate on only 1500 calories. Once you’ve decided you’ve lost the weight you want, or you can’t eat 1500 calories a day any more cause you’re hungry all the time and increase your intake back to 2000 calories, all of a sudden you’re in a surplus and will regain the weight you lost, plus more. ⁠

Don't get discouraged. Weight loss isn't impossible. It just might take longer than expected.⁠