If you're determined to lose weight, choosing healthier foods and counting calories is essential, but you might be surprised that slashing calories to the bare minimum isn't the ticket to weight-loss success. Here's some information and advice on the issue from a board-certified physician who practices in Southern California.

Dear Doctor,
I decided this is the year I will lose that 25 pounds I gained after college. I am dieting and counting calories. I heard that you shouldn’t eat fewer than 1,200 calories a day, and I am wondering why? Can you please explain, because I thought I should eat as little as possible.
— Dieting For Real This Time

This is a great question, and I'm sure that there are other readers who have decided on a similar weight-loss resolution as you have! I commend you on your weight-loss resolution.

The principle behind weight loss is simple: you either have to burn more or eat fewer calories. To lose weight, you need to create an energy (or calorie) deficit by eating fewer calories, increasing the number of calories you burn through physical activity, or both. Typically, what is recommended as the safest method is a combination of eating fewer calories and burning calories through physical activity. While you do report that you are dieting and counting calories, you do not mention that you are doing physical activity and exercise, which, as mentioned above, is so important in the safe weight-loss equation.

Determining a safe daily calorie deficit can be difficult because every person is different when it comes to baseline metabolism, body size and composition, sex, age, and level of physical activity. What is easy to determine, however, is the fact that 3,500 calories equals about one pound of fat. Therefore, you have to burn 3,500 calories more than you take in to lose one pound. For example, if you cut 500 calories from your diet every day, you would lose about one pound a week. Or, if you are physically active, you can eat 250 calories less every day and burn 250 calories per day with your workout. Ideally, you do not want to lose more than one to two pounds per week, which means a safe calorie deficit would be to burn 500 to 1,000 calories per day through a reduced-calorie diet AND exercise.

Determining a safe minimum amount of daily calories can be difficult as well for the same reasons listed above. However, extreme restriction of consumed calories can significantly slow the metabolic rate, and hinder your weight-loss goals. The American College of Sports Medicine states that you shouldn't send signals to your body to conserve calories by detoxing or fasting. They recommend that women should eat at least 1,200 calories per day, and men should eat at least 1,800.

The reason that the metabolic rate slows with prolonged dieting of less than 1,200 calories per day is a chain reaction of physiologic responses to the stress associated with such a restricted diet. Your body initially adapts to the stress of low caloric intake by engaging the "fight or flight" stress response, which has several negative consequences, despite you seeing lower numbers on the scale. The "fight or flight" response stimulates the breakdown of muscle in order to supply the body with enough fuel (glucose) to maintain the blood sugar levels in the absence of sufficient dietary calories. This "fight or flight" stress response will eventually wear out, thus slowing the metabolic rate to compensate for what the body perceives as starvation.

In summary, there are three guidelines to safe and effective weight loss: aerobic physical activity, gradual changes in eating habits to encourage a lifestyle change, and a slow weight loss of one to two pounds per week.

Hopefully, your weight loss questions have been answered with the above information. As always, you should consult with your physician before starting any weight-loss or exercise program. Also, if concerned with dietary or nutritional aspects of weight loss, consulting with a licensed nutritionist or dietitian may be of benefit. Good luck with your continued weight loss!

Dr. Nicol's posts are for informational purposes only and should not be considered medical advice, diagnosis, or treatment recommendations. Click here for more details.