The math and science of weight loss — part 2
Our body weight is essentially the sum of three broad categories — body fat mass, lean mass and extracellular water.
In Part I of this article, “The math and the science of weight gain-Part 1” I explained the nuances of the above three categories of fat. This article goes deeper and illustrates the basal metabolic rate, and the estimated energy requirement per day, so as to enable the reader to estimate their own daily requirements.
There are several ways to estimate one’s BMR. The World Health Organization, for example, uses something called the Schofield equation in their technical reports for estimating BMR. There are other equations as well, such as the Mifflin-St Jeor used by the US Academy of Nutrition. I have illustrated a case for a woman between 30 to 60 years of age as an example in this article.
Below is the Schofield equation for various age groups and based on gender:
BMR = aw + k ∓ e
Where a, k and e are constants that depend on age, gender, as defined below, and e is the standard error.
For example, to estimate the basal metabolic rate for a 40-year-old woman who weighs 55 kgs, according to Schofield, her BMR (in Cal/day) should be estimated as 8.12*W + 845 ± 111, where W is her weight in kg, and 111 is the standard estimation error. So, for a 40-year-old woman who weighs 55 kgs, her BMR should be 8.12*55 +845 ± 111=1296 ± 111, which is anywhere from 1185 to 1407 Cal/day.
Why such a broad range? Subjects leaner and more muscular than usual require more energy than the average. Obese subjects require less. Patients at the young end of the age range for a given equation require more energy. Patients at the high end of the age range for a given equation require less energy. That is where the error of 111 comes into play and needs adjustment, and ideally, a dietician or a physician should be able to help you with your estimate.
Someone who is very active physically needs more energy than a sedentary person. Thus, another adjustment factor should be used depending on how active the person is. The estimated total energy requirement per day (EER) is thus the addition of your BMR + the added energy requirement adjusted depending on your physical activity. It can be calculated as EER = BMR*F, where F is the adjustment factor, and illustrated in the following paragraph.
Again using our above example, if the 40-year-old woman is sedentary then her estimated energy requirement (EER) is BMR (1407 *1.3) = 1829 Cal, and if she is slightly active then (EER) is BMR (1407*1.5) = 2110 Cal and if moderately active — exercise lasting 20–45 minutes at least three times per week, or a job with a lot of walking, or a moderate intensity job then EER is BMR (1407*1.6) = 2251 Cal per day and if she is extra active — engaging in very hard exercise six to seven days a week or have a physical job, daily energy calories needed by the person is BMR ( 1407*1.9) =2673 Cal per day.
Let me summarize. Most of the energy from the food we eat is used to meet the basal metabolism. Some energy is used to sustain daily activities. Any excess usually gets deposited as fat. It is that simple. I am also providing a BMR and energy requirement calculator that can be accessed by clicking here
Let us consider a scenario where our 40-year-old female protagonist is on business travel, and inadvertently snacks on 2 samosas and a masala dosa every evening, on top of her regular food intake. That is an additional 500 calories per day. Over a week, our friend accumulates 3500 cal, which is equivalent to 450 gm of body fat. On the contrary, she could have chosen to lose 500gm weight that week by eating 300 calories less per day and burning an additional 200 calories in the form of physical activity.
Remember, how you maintain your weight is a balancing act. Although it sounds simple, you need to be cautious of hidden calories in some foods. Swapping high-calorie energy-dense foods to low- calorie fibre-rich fruits and vegetables can be a good start towards a healthy dietary change. Similarly, brisk walking 30 minutes a day, every day can be a good start, and you can slowly increase the intensity and frequency depending on your comfort levels to more rigorous or higher-intensity workouts.
Feel free to comment below about your experiences and experiments with body weight.
