Many people asked me to give advice on how to lose weight. I told them that there is no secret, how our body gain and lose weight can be expressed in a simple formula of:
A – B = C!
A = Absorption
B = Burn
C = Cumulate
So, in a nutshell, how much you cumulate as body weight is basically the balance of how much you absorb from the food you eat and how much your body burn.
Absorption (A)
Let’s look at the first variable A, the absorption. To understand this, we need a little bit of knowledge on nutrition. Basically, there are 6 types of essential nutrients that the body needs: carbohydrates, proteins, fats, vitamins, minerals, and water. Of these, carbohydrates, proteins, fats are considered macronutrients, these they are the major components of nutrients that we absorb from our food besides water. Carbohydrates and fats primarily furbish the body with energy and heat. Proteins are the building blocks of our body, and they are used mainly to build and repair body tissues. However, when the body reserve of carbohydrates and fats is low, proteins can also be used to provide energy.
When you eat and digest your food, your digestive system breaks down the foods in various stages. Carbohydrates in foods, including all the starches and sugar, are broken down into simpler sugar components (glucose, galactose, and fructose). Fats are broken down into triglycerides and fatty acids, whereas amino acids are the break down compounds of protein food. Absorption of these nutrients happens in the small intestines, where the nutrients cross over to the blood stream and being carried into the cells of the body. Not 100% of all we eat can be fully absorbed by our digestive system. There are always residual nutrients that escape absorption and being excreted as waste.
Cumulate (C) and Burn (B)
Carbohydrates are the preferred source of energy for our body. Once absorbed, the blood transports glucose from carbohydrates into our cells to burn as energy through a complex process that involved glycolysis and The Krebs Cycle. However, we can’t burn all glucose at once; therefore, the body will convert the glucose into glycogen for storage. 1/3 of the glycogen in our body is stored in the liver, whereas the other 2/3 is in our muscles. Glycogen is slowly converted back into glucose throughout the day to supply our body with energy and heat. The rate of conversion of glycogen to glucose depends on our energy expenses.
Glycogen holds a lot of water and it is easy to convert into glucose, however it is quite bulky. Therefore, the body only stores enough glycogen to provide energy for a short period of time. We only store less than a day of supply to meet our body energy need at rest. If we exercise a lot, then the glycogen supply can only last for a few hours. Therefore, glycogen is the short-term energy reserve. If we start to cumulate too much glycogen, it will be converted to a more compact form of water-free storage mean: FAT. Similarly, if there are abundant carbohydrates in our food, the fats that we eat will be absorbed and transported to fat cells in our body for storage. So, our variable C refers to the accumulation of both glycogen and fat.
The Weight Loss Formula
Our body weight is the total weight of our muscle mass, organs, bone, fat, and water. The weight of our organs and bones normally do not change much once we reach adulthood (except for the loss of bone mass during old age). Therefore, the composition of muscle mass, fat, and water will affect our body weight. To achieve effective weight loss, the target should be to reduce the excess fat storage in our body. So, how to do that? Let’s look at our formula again:
A – B = C
How do we gain weight in the first place? This is because we always maintain a positive C, i.e. A – B > 0. 
We are absorbing more carbohydrates and fats than we need! So, to reverse this process, we want to get to the stage of A – B < 0. This will give us a negative C, so that the body starts to dig into the long term reserve, i.e. fats, for energy. Since the fat storage will not be used until the body has depleted its short-term storage of glycogen, to sustain weight loss, we must maintain A-B < 0 for a significant period of time in order to be effective. Short term measures, such as a one-day fasting or intense exercise for a day, may appear to have an immediate effect of losing 1-2 kg the next day due to the depletion of glycogen and water in the body. These measures will not achieve a long term effect because the fat storage is not touched.
So, how to achieve A-B < 0? The simple answer is to decrease A and increase B. The majority of weight loss programs have to work on one or both of these two variables to achieve weight loss (except liposuction that works on directly cut down the C!)
How do we decrease the absorption (↓A)? We have to achieve this by dieting to control our food intake, especially the intake of carbohydrates and fats. Therefore, there are many diet plans that focusing on low-carb or low-fat to achieve weight loss. Of course, for those who are severely obese, there are also surgical options for restricting absorption, such as Sleeve Gastrectomy or Adjustable Gastric Banding. These surgeries essentially operate on the stomach to reduce the ability of the stomach to digest food [1]. There are also some medications which work on blocking the absorption of nutrients, such as fats from the food, to achieve this [2]. An impaired digestive system can also affect the body’s ability to absorb nutrients. Therefore, sometimes people who suffered from gastrointestinal disorders will lose weight. But, of course, any sensible person will not want that.
How do we increase our burn rate (↑B)? Well, we need to increase our body activities. In the old days, this is not an issue, since people have to walk a lot and works are mostly physically demanding. Nowadays, with the sedentary lifestyle, we have to make an effort to increase our body activities by regular exercising.
Which one is more effective to lose weight? ↓A or ↑B? To answer this question, we will have to do some calculation. We can use the body mass to estimate the energy expenditure under each type of activities. Table 1 shows the amount of energy a person who weighs 68kg will burn in an hour under different type of exercises [3].
The following table (Table 2) shows the amount of energy provided by 3 types of food items 1 cup of cooked white rice, 1 whole chicken leg, and a piece of cheesecake [4].
Using the two pieces of information together, we can calculate the amount of time that a person who weight 68kg will need to burn each food term under different exercise. The following is a summary table (Table 3):
As you can see, you need to run for 8 min just to burn off one cup of rice. If you think that a short walk will help you to burn off the extra piece of cheesecake you take as dessert, then you are wrong! You will need to walk for an hour!
I hope this simple illustration will help to convince you that, to lose weight, it is better to reduce our intake (i.e. ↓A) then trying to burn off the extra calories that we have eaten (i.e. ↑B).
The best approach to weight loss: ↓A + ↑B
If you are looking to lose weight, there is no short cut. You have to work on your diet to reduce your intake, especially your intake of carbohydrates and fats; as well as to increase your energy expenditure at the same time. Furthermore, you will need to put in the effort to sustain your weight loss approach for a period of time. Depending on your weight loss target, you will need in term of months to hit your goal. Any short-term approach will likely be ineffective.
The formula of weight loss is simple. BUT, I am sorry; there is simply no short cut.
References
[1] Griffin, R.M. & Derrer, D.T. (2014, 29 May). Choosing a Type of Weight Loss Surgery. Retrieved 23 April 2015 from http://www.webmd.com/diet/weight-loss-surgery/weight-loss-surgery-making-the-choice?page=1
[2] Goepp, J. (2010, October). Block Absorption of Fat Calories Safely. Life Extension Magazine. Retrieved from http://www.lef.org/magazine/2010/10/block-absorption-fat-calories-safely/page-01?checked=1
[3] BrianMac Sports Coach (n.d.). Energy Expenditure. Retrieved 23 April 2015 from http://www.brianmac.co.uk/energyexp.htm
[4] U.S. Department of Agriculture, Agricultural Research Service. (2014). USDA National Nutrient Database for Standard Reference, Release 27. Nutrient Data Laboratory Home Page, http://www.ars.usda.gov/ba/bhnrc/ndl
very useful article. Thanks a lot!