Understanding Your Metabolic Rate

As found here @ Powerbar.com

Your metabolic rate works a lot like the engine of an automobile except that, unlike a car, your engine must work 24/7 to keep you alive. Some people have a Hemi® under the hood, while others are more like hybrids. Athletes have a keen interest in their metabolic rate or resting energy expenditure because it can help them determine their energy needs and help them lose, maintain or even gain weight.

The nutrition world is full of advice for how to increase your metabolic rate – they tell you to exercise, lift weights, eat hot peppers, drink tea and even develop a nervous twitch. However, new research shows that your body’s metabolism is largely determined by factors that you cannot change—like the size of your liver, spleen, heart, lungs and brain—and that the many suggested ways to increase metabolic rate have little, if any, effect.

Below are some key points about the metabolic rate concept and the truth behind what really increases or decreases it from a research presentation given at a body composition meeting held by the Sports, Cardiovascular and Wellness Nutritionists (SCAN) at the American Dietetic Association’s Annual Conference in St. Louis, MO, this past October.

What is your metabolic rate? Your metabolic rate is measured as either the basal metabolic rate (BMR) or resting metabolic rate (RMR). The BMR is usually measured in the morning after an overnight fast and lying down for 30 minutes whereas the RMR is often measured in the afternoon, several hours after eating. It generally provides a result that is 10-20% higher than the BMR. Both are values that describe how much energy your body needs to sustain itself.

The RMR, or BMR, represents about two-thirds of your total daily energy needs. Muscle movement (exercise, fidgeting, walking and daily activities) represents about 23 percent of the total energy expenditure in the average American, while the thermic effect of food (the energy used to turn food into usable energy and waste) represents another 10 percent. Only very active individuals can match or surpass their RMR with calories expended from their physical activities.

Do thinner people have higher metabolic rates? Nope. In fact, the opposite is true. One effective way to increase your metabolic rate is to actually gain weight. That’s because both fat and muscle require energy to sustain themselves. And, for every pound you gain, one-quarter of it is generally lean tissue.

The same thing applies for when you lose weight – for every pound lost, one-quarter of it is lean tissue. That’s why when you lose weight, for every pound lost, your body requires about 10 fewer calories. Lose 10 pounds and you now need to cut 100 calories from your diet (or burn an additional 100 calories through exercise) to maintain your weight. This is part of the reason why weight maintenance is so much more challenging than actually losing weight.

Doesn’t aerobic exercise or resistance training accelerate your metabolic rate? If this were true, fit individuals would have higher metabolic rates than an unfit person of the same size and sex. Research shows this isn’t the case. Even highly trained athletes often have RMR equal to their sedentary counterparts. While exercise is great for total energy expenditure, is good for your heart and cardiovascular system and has many other health benefits, increasing the metabolic rate is not one of the major benefits of exercise.

Does adding muscle mass increase your metabolic rate? Compared to fat tissue, muscle mass is more metabolically active. But in comparison to organs, your muscles are like a hybrid car while your organs are gas-guzzling V8s. Muscles burn about 13 calories per kilogram of bodyweight per day (kcal/kg/day), fat burns 4.5 kcal/kg/day, but organs burn 200 to 400 kcal/kg/day. In the end, your organs represent 60-70% of your metabolic rate and muscles represent 16-22%.

So the most muscle mass that you can realistically add in a year (4-5 pounds of muscle) would add just 28-50 kcals to your metabolic rate per day.

Should I have my metabolic rate measured? If you are trying to lose weight, it’s probably not a bad idea to get your metabolic rate measured. In fact, many health clubs now offer on-site testing. At the very least, it will probably tell you that your weight woes are not due to a low metabolism. You can also estimate your BMR fairly accurately using the formula below:

Estimating your Metabolic Rate
To estimate your metabolic rate, follow these steps:

Convert your height to meters and weight to kilograms
Height to meters = inches x .0254
Weight in kilograms = pounds/ 2.2
Estimate your Basal Metabolic Rate
Men: BMR = 294 - (3.8 x age) + (456.4 x height) + (10.12 x weight)
Women: BMR = 247 - (2.67 x age) + (401 x height) + (8.6 x weight)
For example, Matt (31) is a 6'2" triathlete who weighs 198 pounds.
Matt's height: 74 inches x .0254 = 1.88 meters
Matt's weight: 198 pounds/ 2.2 = 90 kilograms
Matt's estimated BMR = 294 - (3.8 x 31 years) + 456.6 x 1.88 meters) +
(10.12 x 90 kilograms) = 1,943 kcals/day

In fact, Matt had his BMR tested and it was measured at 2000 kcals/day, very close to his calculated BMR.

Estimating your Total Caloric Expenditure
To estimate total caloric expenditure, you need to factor in the energy expenditure of your daily activity and exercise.

BMR x 1.5 = Weight maintenance for people who do little exercise
BMR x 1.7 = Weight maintenance for moderately active people (up to
1 hour per day of activity)
BMR x 1.9-2.5 = Weight maintenance for athletes

Matt, the triathlete, is very active, exercising for over two hours most days so his estimated total daily caloric expenditure is estimated as follows.

Matt's Total Caloric Expenditure Estimation =
1943 kcals/day x 1.9-2.5 = 3692 to 4858 kcal/day

But Matt is also trying to lose weight. If Matt bases his caloric intake on an activity factor of 1.7 to 1.9:

1943 kcals/day x 1.7-1.9 = 3303 to 3692 kcal/day

Applying this, he should be able to lose about one pound per week. The effects of this caloric intake would need to be monitored and adjusted according to his rate of weight loss per week.

For people with lower levels of activity, adjusting daily caloric intake below the estimated daily caloric expenditure should bring about weight loss. For example, for people who do little exercise:

BMR x 1.0 = Weight Loss of about 1 pound per week
BMR x 1.3 = Weight loss of about 1/2 pound per week

Again, the effects of this caloric intake should be monitored and adjusted according to the rate of weight loss per week. See this month's Ask the Nutritionist to help determine if or when you should seek individualized professional nutritional guidance.