Know your Basal Metabolic Rate

June 08, 2015

Do you know your Basal Metabolic Rate? 

 Reference: Wikipedia,  Physiology Reviews 

 We use about 60% of our calorie needs each day just staying alive.   The fuel needed to keep us warm, to keep our brains functioning, our heart pumping, our hair growing, our gut moving – all of that, is your basal rate.   Measuring it exactly is a bit tricky because one needs to measure the amount of carbon dioxide you exhale, (how much you are burning) when you aren’t digesting food, aren’t alarmed, angry, upset, in an environment of supportive temperature – and each of those elements has proponents and arguments. 

Finally, fat tissue needs to be extracted. Because women biologically have more fat, their weight is a bit higher so in general, a correction needs to be made for that.   As we age, our muscle mass declines, and our rate of exercise declines.   We need less fuel, or we gain weight. There are several schools of thought with varying formulas.   I will refer you to each of them with links so you can calculate your own. It should be noted, however, that in every review, they find as much as 25% inter-subject variability, even in the most controlled environment.   

Some of us just need less. (So we get fat, faster. We survive starvation, longer.) And now, the literature on underreporting of calories is starting to ramp up too. The Mifflin St. Jeor Equation is as follows: (My favorite) For men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5 For women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161 The Katch-McCardle Formula depends on knowing your percent body fat. BMR (both men and women) = 370 + ( 21.6 x lean body mass in kg ) Harris Benedict Formula simply converts your activity level with a predictive formula.

To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:If you are sedentary (little or no exercise) : Calorie-Calculation = BMR x 1.2•   If you are lightly active (light exercise/sports 1-3 days/week) : Calorie-Calculation = BMR x 1.375 •   If you are moderately active (moderate exercise/sports 3-5 days/week) : Calorie-Calculation = BMR x 1.55 •   If you are very active (hard exercise/sports 6-7 days a week) : Calorie-Calculation = BMR x 1.725 •   If you are extra active (very hard exercise/sports & physical job or 2x training) : Calorie-Calculation = BMR x 1.9

Each of these has proponents and detractors. Depending on what you want to do. If you want to lose weight, you need to be eating less than you are burning – and you need to be getting access to your fat energy. The only way to do that is to turn off insulin.   Without insulin, your fat cells open up and share freely. With insulin, your fat cells are shut and you only have 1500 calories of carbs to burn before you are starving hungry, hypoglycemic and ready to eat the furniture. WWW. What will work for me.   

I like the Mifflin St. Jeor Equation the best.   I had a monster exercise day on Saturday, biking 18 miles in the Tour de Marsh in Horicon. That allowed me to have 800 extra calories for the day, without gaining weight.   But the Harris Benedict formula comes close.   It also explains to me why petit women (say, 5’3”, who are overweight (say 165)) gain weight when eating 1600 calories a day, with little to no exercise.   We all aren’t the same, and taking into account our age, body fat and exercise level gives us a reality check. Or maybe, as we get older, our denial of what we are eating increases as patterns deepen. This getting older stuff and needing less calories is a drag! 

 Pop Quiz:

  1. My basal metabolic rate is the calories I burn doing nothing but staying alive. T or F.       Answer:   True
  1. As we age, we need fewer calories because our bodies shrink, our muscles shrink, we aren’t as active. T or F                               Answer:   T (See, it’s easy to get an A)
  1. The formulas can vary depending on your body fat percentage and gender. T or F.        Answer:    True
  1. Activity allows you to consume more calories. T or F                     Answer:   True. Makes it almost worthwhile
  1. Despite all our careful measurement, there remains a 25% error rate in our prediction of what our calorie need is. T or F                    Answer:   True
  1. This variability may be because we underreport our calories when asked to recall what we ate. T or F                      Answer:    True