After childhood, most of us have had pretty sedentary lifestyles and before we could think about it, fat loss did become a big concern for most of us. In this write-up, we’ll go through a very simple model which will help YOU achieve your fat loss goals. In future parts, we’ll address some commonly asked questions and popularly floating myths about this heavily discussed topic. Before we get into how you can modify your diet so that you become the master of the weighing scale and measuring tape reading, let’s start off by understanding the relation between fat-storage and energy balance in the human body.
What is fat?
Fat, under a group of organic compounds called triglycerides, is one of the three main macro-nutrients needed by our body. Commonly, fat is seen in two formats — Dietary fat and Body fat.
Dietary fat i.e. fat found in food is a major energy source for the body. Typically, energy from fat intake comprises 15–70% of the total energy consumed by a person via food in a day.
On the other hand, Body fat exists as an insoluble substance inside fat cells (lipids inside adipose tissue). Body fat serves as an energy reserve, cushioning and insulation for the body while also serving important endocrine (hormonal) functions.
How does fat gain/loss work?
Think of the body as an accumulator of energy where the Input is the food you eat and Output is simply… life. You are alive because the cells inside your body are functioning. These cells need ATP to function. The ATP cycle runs on energy from blood which, in turn, is just energy absorbed from food.
Energy from food and the energy associated with the human body are commonly measured in Calories (1 Calorie = 1 kilo-calorie = 1000 cal = 4200 joules).
1. How much energy do you need for normal function each day?
Even while you stay immobile on your bed, you will keep burning energy. The total amount you burn in one complete day on bed is known as Basal Metabolic Rate (BMR). This value primarily depends on the amounts of various types of tissues that the person has in his/her body. Normally, larger people have more muscle and fat, larger organs, etc and hence would be expected to have a higher BMR. Women, on an average, are shorter than men and hence have less tissue of each type and thus, have a lower BMR than men. Typically, women have BMR in the range 1100–1500 Cal and men have it at about 1600–2100 Cal.
Every activity you do which involves moving, even simple ones like standing, walking and wearing clothes needs energy. This is because your heart, lung and skeletal muscles demand more during and after the activity. Sometimes, strenuous activities might be followed by repair mechanisms getting triggered in the body and this requires more energy too.
The total energy that you use up in a day is the sum of your BMR and the energy you burn from the activities you do.This total is a very important quantity called Maintenance Calories.
Maintenance Calories = BMR + Activity
Tracking the contribution of activities to your Maintenance Calories would be very cumbersome. Instead, a very nice technique that’s used for estimating Activity is to scale the BMR based on the lifestyle of the individual. For example, a very sedentary person would burn only 20% of their BMR as activity throughout the day; making the total Maintenance Calories 1.2 x BMR i.e. BMR + (20% of BMR). The same would probably be around 1.4 x BMR for someone who regularly does vigorous workouts.
Using the scaling technique above and considering different types of tissues in your body, an Excel sheet has been created (available below). YOUR Maintenance Calories (in this current phase of life) can be fairly well estimated by just inputting your gender and some numbers into the sheet.
There is an alternate, slightly more complicated model where, a quantity called Total Daily Energy Expenditure (TDEE) is used as the basis instead of Maintenance Calories. For most practical purposes, especially for someone who is just beginning to understand fat loss, this Calorie model will serve the purpose. But, for the curious, I will explain TDEE method in future.
2. How much energy does the food I eat provide?
The nutrients we get from food are classified into two categories — Macronutrients and Micronutrients. Macronutrients like Carbohydrate, Fat, Protein and Fibre are normally consumed in relatively larger quantities (few 10s of grams per day) compared to Micronutrients like Vitamins and Minerals (micrograms to few grams per day). All your Energy intake (aka Input above) comes from Macronutrients — specifically Carbs, Fat and Protein:
Carbs
- 4 Cal per gram | Easy-to-digest energy source
Fat
- 9 Cal per gram | Big energy source
- More satiating than Carbs (i.e. keeps you fuller)
Protein
- 4 Cal per gram | Primarily building blocks of the body
- Any excess is used as an energy source (although difficult to process)
- Most satiating macro-nutrient
Exception: Alcohol contains energy too: but, let’s not consider it a ‘nutrient’.
3. What happens when there is an imbalance between how much I burn and how much I eat?
Fat stores are like long term Energy Buffers for the body. We have evolved to store fat so that in case of a starvation scenario, we still have good energy reserves. On the other hand, any excess energy consumed is going to be proportionally stored as Body Fat. The simple rule for energy is:
Intake — Maintenance = Store as Fat (if intake is higher)
Maintenance — Intake = Burn Fat (if input is lower)
Here, Output is the total energy you burn throughout the day (Maintenance Calories) and Input is the total energy you consume via food.
4. How many calories fewer should I consume to lose 1 kg of fat?
Every 7.7 Calories consumed in excess would eventually contribute to 1 gram gain in total Body Fat and vice versa
Therefore, if you eat 1000 Cal more than your Maintenance intake everyday for 8 days, you’ll gain about 1 kg of body weight as fat. Fat loss works in a very similar fashion. If you eat 500 Cal less than your Maintenance, you’ll lose 1 kg of body fat in about 15 days.
The reason Maintenance Calories is named so is because this is the amount one needs to eat in order to maintain (i.e. neither gain nor lose) Body Fat.
A Summary
If your Calorie intake is greater than your Maintenance Calories, you are said to be on a Caloric Surplus: the opposite is called as being on a Caloric Deficit. These are important terms that we will frequently encounter in future.
Fat loss, as we see, is simply a game of Energy Balance.
A Deficit lifestyle is what is will ensure that you stay relatively lean.
