Metabolism and Daily Caloric Requirement
by Max Wettstein, Copyright 2012
“I have the metabolism of a hibernating bear.” This is how one of my fellow pilots describes himself, as he psyches up for another round of cardio on the hotel elliptical-trainer. Does this sound like a fitting description for you? Perhaps you’ve been genetically blessed with a fast metabolism, more like that of a hummingbird, and your only issue with calories is consuming enough of them. Our metabolism is the single biggest factor in determining our daily caloric requirement. Our caloric requirement does vary day to day depending on our activity level, but our ‘resting’ caloric requirement can only be changed by altering our metabolism. Genetics play a huge role in determining metabolism, but there are many other factors that affect metabolism that you can take advantage of.
Metabolism is defined as the sum of all physical and chemical changes involving energy and material transformations that occur within all our living cells. Each cell has its own energy production center known as the mitochondria, and it is this collective energy production of all cell mitochondria that determines metabolic rate. Along with energy production, two fundamental processes of metabolism are anabolism and catabolism: building up tissue and breaking it down, respectively.
When discussing metabolism, it makes sense to begin with our resting metabolism for simplification. Our metabolism while at complete rest is known as our Basal metabolic rate, or BMR. Our BMR is affected by many factors, many of which we can influence. These factors in no particular order include but are not limited to: genetics, gender, age, body-type, diet, body temperature, environment, hormones, and body-fat percentage/lean-body mass. More discussion on this later, but you’ll see why your lean-body mass has the greatest effect of all, aside from genetics, in determining your BMR. Muscle burns calories at rest, while fat does not.
For simplification, we’re focusing on ways to increase BMR, or resting metabolic rate, so we can burn more calories while sitting around playing Solitaire. But let’s take a moment to discuss exercise as a factor in increasing BMR. Although we’re clearly not at rest during exercise, a long-lasting effect on our BMR occurs after we finish our session. Exercise provides a 3-fold, lasting benefit to boost metabolism. First you burn calories during the exercise session itself. Secondly, your metabolism stays slightly elevated for several hours after your session depending on the intensity and duration. Thirdly, after a nutritious recovery meal and a good night’s sleep, you build muscle tissue while your body repairs itself, further increasing your lean-body mass. Once again we see the fundamental role of exercise in our overall health and fitness.
Factors affecting BMR:
Determining your BMR and total daily caloric requirement:
Women: BMR = 655 + (9.6 X weight in kg) + (1.8 X height in cm) – (4.7 X age in years).
Men: BMR = 66 + (13.7 X weight in kg) + (5 X height in cm) – (6.8 X age in years)
*1 inch = 2.54 cm *1 kilogram = 2.2 pounds
Men and Women: BMR = 370 + (21.6 X lean mass in kg)
For both men and women, Total Daily Caloric Requirement = BMR multiplied by …
1.2 if you’re sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, and 1.9 if you’re extra active.
*Sedentary = little or no exercise. Lightly active = light exercise/sports 1-3 days per week. Moderately active = moderate exercise/sports 3-5 days per week. Very active = hard exercise/sports 6-7 days per week. Extra active = very hard daily exercise/sports & physical job or 2X day training.
So you may have been born an ‘Endomorph/Neanderthal-type’ with the metabolism of a hibernating bear, but there is still hope for you even if you can’t change your genetics. The moral of the story is, exercise to maintain your muscle mass so you will burn more calories at rest, and divide your total daily caloric intake into smaller more frequent meals. Careful that you’re not just eating more food in the process though! Keep the furnace stoked but not stuffed, with quality food choices. As we age, keeping our body-fat down gets more and more challenging, but it really is a matter of maintaining your lean-body mass that ultimately determines your metabolic rate.
Sources: www.weight-loss-i.com; ‘FitnessWave’ Mobile Hydrostatic Body Fat Testing; ‘Encyclopedia of Modern Body Building’ by Arnold Schwarzenegger; ‘The Complete Nutrition Guide’ by the MT Sinai School of Medicine.
Back to Max Wettstein Health and Fitness Library