The math and science behind weight loss
I have studied my own body weight over the years. Our body weight is essentially the sum of three broad categories — body fat mass, lean mass and extracellular water. In the following paragraphs, I will illustrate how each of these contributes to your body weight.
1. Weight gain due to body fat mass
Body fat mass is the fat present in the body, lean mass comprises muscles and organs like the liver, spleen, kidneys, and bones, and extracellular water is the water present external to the cells in the intercellular spaces. Overall weight gain or loss can involve any of these three categories. Let me go deeper into each of these categories.
It is common knowledge that there needs to be a balance between what we eat and how much we burn. For a person who eats more and burns less, she tends to gain weight. When energy intake in the form of food calories exceeds energy expenditure, the body stores the excess energy as fat. This could sometimes result in obesity.
This leads to the often asked question of how much energy is needed on a daily basis. Everyone needs a certain amount of energy to keep their body functioning (to breathe, keep the heart pumping, circulate blood, cell growth, and for the brain to function) at all times. This is the basal metabolic rate (BMR). In other words, it is the amount of energy you burn even if you are just sitting or sleeping all day. BMR is not a unique number but really depends on your weight, height, age, genetics, gender and muscle mass among other factors.
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 a sequel to this article.
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 depending on whether the person is sedentary, slightly active, moderately active or very active, the adjustment factor is multiplied. This is again illustrated in another article. Now that you understand BMR and EER, I have made it easier for you to estimate your BMR and EER in this calculator.
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.
It is imperative you understand how much food your body needs on a daily basis. Eating additional food on a long term basis can lead to obesity. Obesity in societies where food shortages were common, was considered an indication of affluence and wealth. Even today, in some rural areas of Mauritania and Western Sahara, extra body fat is admired and pubescent girls are sent to fattening huts to make them more plump and desirable for marriage by making them eat unusually large portions of food.
As a side note, it is well known that popular film actors or boxers lose as much as 10 kg over a two month period to meet their professional objectives. They achieve that by a potent combination of diet and exercise.
Please recall the three categories of body weight that I highlighted earlier. I have already explained the body fat mass. Let me now touch upon the other two categories of body weight — lean (muscle) mass and extracellular water.
2. Weight gain due to increased muscle mass
A useful form of weight gain is the gain in muscle mass. Exercise, especially resistance training increases your muscle mass. With regular physical activity such as walking, swimming, running or strength training, one tends to reduce the body fat, but gain muscle mass simultaneously. Let us understand how this phenomenon works.
The primary building blocks for muscles are proteins. So it goes without saying that during a period of increasing muscle mass, the muscles need to be nourished and supplemented with protein-containing foods. The muscles ingest the extra proteins from the bloodstream to build new muscle fibers. This is the reason trainers advocate increased protein intake when you are doing more of strength training.
So do not panic if you don’t see a change in your weight after weeks of physical activity, especially if your primary objective is weight loss. Earning yourself a well-toned and sculpted body with a smaller waistline definitely counts as a positive change.
3. Weight gain due to increased water
Several times in your life, you may experience a bloated feeling, sometimes with swollen hands and feet. One of the reasons for that could be the extra salty food that you consumed the night before. Whenever there is excess salt in the body, the body tries to hold on to excess water to dilute the additional salt. The kidney regulates the water and ion balance in the body, and holds on to the excess water around the blood vessels — in extracellular space and in the extremities. It finally flushes it out when the balance is restored. As counterintuitive as it may sound, the body also holds on to the water when one is dehydrated as the salt water balance is again lost, and it holds on to water until the balance is restored in the form of oral rehydration solution (ORS).
While these instances illustrate the mechanism of temporary retention of water, chronic water retention in the body can occur due to kidney disease or chronic heart failure. As a piece of general wellness advice, it is best to avoid salty foods.
