(Editor’s note: Today’s guest blogger is Donna H. Ryan, M.D., Associate Executive Director for Clinical Research at the Pennington Biomedical Research Center)
One of the most difficult aspects in counseling for weight loss is agreeing on an achievable goal with my patients. My standard recommendation is to set a weight loss goal of 10 percent and set it for six months. Patients usually think this is too little. My average patient is 220 pounds, and that's a weight loss of 22 pounds in six months, about a pound a week. Many times patients want to lose 50 pounds, or even more, so it takes some convincing that 10 percent is a good goal. Frequently, people set their expectations too high at 20 percent or 30 percent. I always tell the patient, if we can make the 10% goal, then we can set another goal! There is no limit on the number of goals, but the key is to achieve the first goal.
People often ask me how many calories they should aim for to lose weight, and I usually tell them we think it is achievable to sustain a 500- to 800-calorie per day deficit during the weight loss phase. Over seven days that means 3,500 to 5,600 calories, or one to 1 1/2 pounds lost. We like that weight loss because it is usually something people can live with over a reasonable period of six months or so to enable them to reach that realistic weight loss goal of 10 percent.
The next questions that usually follow are: How many total calories does it take to maintain my weight? How much do I aim to achieve the 500-800 calorie deficit?
Determining calorie needs can be a challenge. We have done studies where we try to define energy needs as accurately as possible, and a number of challenges make it difficult. By far the biggest variable is the amount of physical activity that people do. There is also the challenge imposed by the reduction in metabolic rate that the reduced obese state imposes. This means that as you lose weight, your metabolism slows, and you actually require fewer calories to maintain the weight.
A useful rule of thumb is that it takes about 10 calories per pound to maintain your weight. So for that 220-pound person, that's 2,200 calories a day. You can subtract 500-800 calories to promote weight loss and/or maintenance.
I find that using round numbers such as 1,200-1,500 calories for most women, and 1,500-1,800 calories for most men is usually effective. Patients need to understand that at a lower weight they actually need fewer calories. Of course, very active people need more. But, again, most people are not active and tend to overestimate what they are doing. What most people fail to understand is that even if we have the best technology available to estimate energy needs, most people do a poor job at estimating energy intake.
Yes, there are many formulas to estimate calorie needs per day, but none is perfect. The Harris Benedict is one of the most common, but it is quite complicated.
A much easier approach is to use 10 calories per pound of body weight as an estimate of calorie needs – independent of exercise or other activities.
Here is how to use the formula:
The Harris Benedict Formula for estimating Basal Metabolic Rate (BMR):
BMR (Kcal)=66 + (13.8 x weight in kg) + (5 x height in cm) – (6.8 x age)
BMR (Kcal)=655 + (9.6 x weight in kg) + (1.8 x height in cm) – (4.7 x age)
To estimate total daily energy expenditure, we must multiply the Basal Metabolic rate with an Activity Factor:
Daily energy expenditure (kcal) = Basal Metabolic Rate * Activity Factor
Activity factors range from 1.3 for sedentary, 1.5 for lightly active, 1.6 for moderately active and can be up to 2.5 for athletes. Most people use 1.3 because most people are pretty sedentary and tend to overestimate the amount of activity they get. In general, 1 mile usually burns about 100 calories.
Here is an example for a 50-year-old female, 200 pounds and 60 inches tall:
Harris Benedict Formula for estimating Basal Metabolic Rate:
BMR (Kcal) = 655 + (9.6 x weight in kg 91) + (1.8 x height in cm 152) – (4.7 x age 50) = 1567
To get daily energy expenditure, multiply the BMR with an activity factor:
1567 * Activity factor of 1.3 = 2037 calories
So, my long-winded explanation will have to end with a statement that the bottom line is the scale. We encourage self-monitoring, and daily weights. We ask people to keep a record of their daily weights and adjust their eating/activity behaviors daily in response to that they see on the scale. For a trend upward, no matter what we have constructed at the energy intake goal, we cut back!
Congratulations to Chancellor Richardson on his improved health and lifestyle! And best of luck to all those who are emulating him. You can lose weight and improve your eating and exercise behaviors. I hope this explanation is helpful to all of you in achieving your goals.