How many calories should I eat and how often should I exercise for optimal weight loss?

The number of calories each person needs in order to maintain their weight varies based on gender, age, weight, height, and activity level.  Several programs are available to help you approximate your calorie needs. However, if you want to do the math yourself simply grab a calculator and plug your information into the following calculation.  This formula is called the Mifflin-St Jeor equation, and studies have found that it is the most accurate in approximating caloric needs.

The Math

For men:  RMR = 9.99 x wt (kg) + 6.25 x ht (cm) – 4.92 x age (yrs) + 5

For women: RMR = 9.99 x wt (kg) + 6.25 x ht (cm) -4.92 x age (yrs) – 161

Convert pounds to kilograms by dividing by 2.2.  Convert inches to centimeters by multiplying by 2.545.  Moderately active people are generally advised to consume about 1.5 to 1.7 times the calculated resting metabolic rate (RMR).

Breaking down weight loss

The numerical caloric value that you have now represents the number of calories you need to eat to maintain your current weight.  In order to lose one pound, you need to create a 3500 calorie deficit. This can come either from decreasing caloric intake, increasing caloric expenditure, or ideally both.  For example, if you want to lose a pound per week, try cutting out about 500 calories per day through both diet and exercise.  This could mean running 2 miles (about 200 calorie expenditure) and skipping dessert, which generally packs around 300 calories.  But remember – losing weight is not the hard part.  The hard part is keeping the weight off.  It is well-established that people who are most successful at maintaining weight loss are people who engage in regular physical activity. 

Exercise is key

The USDA 2005 Dietary Guidelines suggest that adults aiming to maintain weight loss should engage in 60-90 minutes of moderate physical activity most days of the week.  While this may be overwhelming to hear for some people, especially those who are completely sedentary, it is important to note that you can gradually build up to this goal by starting with 15-30 minute bouts of enjoyable activity. 

Want to get started?

If you’re looking for a motivating way to kick off your exercise program, try this easy to follow 12-week workout, complete with step by step instruction from the ACE experts.

Natalie Digate Muth, MD, MPH, RD, is a registered dietitian and recent graduate of the UNC School of Medicine. She is an ACE-certified Personal Trainer and Group Fitness Instructor, and holds additional certifications with the American College of Sports Medicine and the National Strength and Conditioning Association. She has made several appearances as a nutrition expert on CW's San Diego 6, been quoted as a fitness expert in the New York Times and other newspapers and is an ACE Master Trainer and award-winning author. She is currently a pediatrics intern at UCLA Mattel Children’s Hospital.