Losing weight is nothing mysterious. It lies in a basic physics law–energy intake should be less than energy expenditure. In plain English, if you eat fewer calories and spend more energy, you will lose your weight.

One popular idea is that you should lose your weight GRADUALLY –the slower, the better. For example, some advisors from MyFoodDiary.com suggest that if every day you reduce energy intake by 250 kcal and increase energy expenditure by 250 kcal, you will create an energy deficiency of 3,500 kcal in a week, and you will lose 1 lb fat. They also claim that when you lose weight slowly, you won’t lose too much muscle mass, and the body will not over-adjust the metabolic rate. It sounds biologically perfect.

However, not all of the above advice is correct. You may be surprised to see how ineffective such a moderate plan works for you. First, You need to know your energy balance point. If you are gaining weight now, your energy intake is greater than the energy expenditure. Simply reducing 500 kcal per day is likely not enough. Second, even if an energy deficiency of 500 kcal does decrease your weight, it takes too long to achieve any meaningful result. You may easily become frustrated when your weight seems to go nowhere. Third, when you are losing weight, you are lowering your energy balance point too. The weight loss effect of reducing 500 kcal per day will diminish gradually. Fourth, when you lose weight, you will get ride of not only fat but also water and muscle mass. The ratio of muscle mass loss versus fat mass loss is quite constant. Thus, even if you lose weight slowly, you will end up losing pretty much the same amount of fat and muscle mass as that of losing weight quickly.

Finally, the metabolic reaction to weight loss is only partially true. If you lose weight only through restricting calorie intake, your body may indeed lower the metabolic rate to preserve energy just like during starvation. However, if you combine calorie restriction with exercise, your body won’t necessarily decrease the metabolic rate. Human metabolic rate is determined by basal metabolic rate, feeding thermogenesis, and physical activity. Increasing physical activity will raise your basal metabolic rate too, thus partially offsetting the metabolic effect of weight loss. In addition, unless you adopt a very low calorie diet (<800 kcal per day), a moderate low calorie diet (1,200 kcal per day) won’t affect the total metabolic rate too much.

My weight loss prescription will be like this. For an average overweight people (BMI of 28, less than 200 lb), the energy balance point is about 2,000 kcal per day. By reducing energy intake to 1,200 kcal per day, you instantly create an energy deficiency of 800 kcal per day, which is equivalent to running for almost 2 hours at 12 min/mile. Together with spending 250 to 400 kcal in physical activities, you can safely create an energy deficiency of 1,000 kcal per day, about 7,000 kcal per week. This amount of energy deficiency will result in at least 2 lb weight loss per week. This is a serious and satisfactory weight loss.

I am not promoting an extreme weight loss program. Extreme low calorie diet (<800 kcal per day) and vigorous exercise may create an energy deficiency of 1,500 kcal or more per day, but the side-effects will be more severe. In this case, human body may indeed reduce the metabolic rate by 30% or more. I have tried it myself and could not stand it. I felt too hungry and too absent-minded to keep up daily activities. The extreme program should not be your first choice.

Weight loss is not easy. Don’t expect 500 kcal less a day can achieve your goal. It never happens.