How Much Should I Be Eating?

By Elise M. Brett, MD, FACE, CNSP


No one enjoys counting calories. Everyone wants an easy solution to weight management. That’s why diets such as Atkins™ and The South Beach Diet® are so popular. They don’t involve counting calories; you just have to follow the rules. These diets often work in the short-term because by banning certain foods total calorie intake for the day is reduced. But eventually, they most often fail either because they are difficult to stick to or because one manages to overeat the allowed foods. If you truly want to lose weight, it all boils down to calories in vs. calories out, no matter where the calories come from.

So, what is a calorie? A calorie is a unit of energy. It is defined as the amount of energy required to raise the temperature of 1 kg of water 1 degree centigrade. How many calories does one need in a day to maintain weight? To lose weight? Several factors affect the amount of calories you burn in a day. To understand this, we must first define resting energy expenditure (REE). The REE is the amount of calories you would burn each day if you were to do nothing but rest. This is determined by factors such as your weight, height, age, and amount of lean body mass. The more you weigh, the taller you are, the younger you are, and the more muscular you are - the more calories you burn. The rest of the calories burned is based on your level of physical activity with slight contribution from other “thermic” factors such as food intake and exposure to cold. The REE is generally around 10-12 calories per pound for normal weight individuals.

There are several ways to estimate daily caloric requirement. If your weight is normal and you just want to maintain your weight, one easy way is to determine your weight in kilograms (divide pounds by 2.2) and multiply by 30. Very active people may need a little more and sedentary people need less but this is usually a close estimate. Most adult women need 1600-1800 kcal/day for weight maintenance and most men need 2000-2200 kcal/day.

A more individualized way to estimate daily needs is to use a predictive equation to calculate REE such as the Harris-Benedict or Mifflin-St Jeor equations which are based on a person’s weight, height, and age. The REE is then multiplied by an activity factor. These equations can be found on the internet.

An even more accurate way to determine REE is using a method called indirect calorimetry which measures a person’s oxygen consumption and carbon dioxide production at rest. These days some weight loss clinics and gyms have small handheld devices which measure a person’s oxygen consumption and give a close estimate of FREE.

Once you have determined your daily energy expenditure, you can eat that many calories each day to maintain your weight or reduce the total amount by 500 per day for weight loss. It is important to understand that there is substantial unexplained variability in these predictive equations that may be due to genetics, ethnicity, weight history or other factors. If these calculations do not work for you, adjust calorie intake up or down based on your body’s response.

Probably the most effective way to determine how many calories you need to eat per day to lose weight is to calculate the amount of calories you have been eating and reduce that by 500 per day. Since 3500 kcal equals one pound, this typically results in 1 pound per week of weight loss. Although this doesn’t sound like much, this is a safe and attainable rate of weight loss. Studies have shown that most women need 1000-1200 kcal per day to lose weight and men 1500-1800.

Looking up calorie amounts helps one pay more attention to foods that need to be eaten in more limited amounts. Plus if a diet is not working, tallying up daily calories can help determine a new caloric target. There are numerous calorie reference sources available in print, online and on handheld electronic devices. The bottom line is: if you want to lose weight, eat fewer calories.

Dr. Elise Brett received her medical degree from Mount Sinai School of Medicine. She completed her internal medicine residency and fellowship training in Endocrinology and Metabolism at the Mount Sinai Hospital. She is currently in private practice in Manhattan and is Associate Clinical Professor at Mount Sinai School of Medicine. She is co-editor of the American College of Endocrinology’s Power of Prevention: The Complete Guide to Lifelong Nutrition.