Why You Need A Caloric Deficit For Fat Loss

The Fundamentals comprised of varying topics that get you started on the basics and provide you with a general understanding of fat loss; The Fat Burning Series, as the name suggests, consists of a set of articles that focus strictly on the core factors essential to fat loss. Rather than having one long and massive article, the series is divided into manageable parts that make it easier to progress through. This should aid in clarity and understanding.

Part 1 of the Series discusses Calorie Requirements and Select Foods for Fat Loss.

Defining A Caloric Deficit

At the core of fat loss is a caloric deficit. To begin with, each individual requires a certain number of calories (a unit of food energy) consumed to maintain their current weight or body fat. This calorie intake value varies for everyone, because it is based on individual factors such as a person's current gender, age, height, weight, daily activity level and energy output. This value also changes when one of these factors changes over time. Whenever someone eats (calories in) just as much calories as they burn off (calories out) based on their current body stats, they are said to be eating at their caloric maintenance requirement (or level). Eating at maintenance is what helps a person maintain their average weight on a daily basis.

A caloric deficit can then be defined as your caloric input being lower than your caloric output, thereby creating a caloric net balance (calories in - calories out) that is negative in value:

Caloric Input < Caloric Output

Caloric Net Balance is -ve: Caloric Deficit

Caloric Input = Caloric Output

Caloric Net Balance is 0: Caloric Maintenance Level

Caloric Input > Caloric Output

Caloric Net Balance is +ve: Caloric Surplus

Whenever caloric input is less than caloric output, the caloric net balance is always negative, and a caloric deficit is created.

The Food We Eat, Part 1: A Breakdown

When you eat food, it is broken down by your body for use as an immediate source of energy, or stored for later use. Carbohydrates (primary energy source) are broken down and form glucose for immediate use by the body; any glucose not immediately used or needed are stored as glycogen in the liver and muscles. This process is called glycogenesis. Fats (secondary energy source) are broken down into fatty acids; any fatty acids not immediately used are stored as triglycerides in fat cells. Proteins are broken down into amino acids. It is also important to note that when we eat excess calories above our caloric maintenance level (caloric surplus), some of these excess carbohydrates and proteins are converted and stored as fat.

Glucose is the main source of energy for the body, and when it becomes exhausted, the body begins breaking down its internal energy reserves (which were broken down and stored from the food you ate) to convert to fuel. The breakdown of complex organic molecules to simpler ones for the purpose of energy is called catabolism. The order in which the body generally begins to tap into its reserves is carbohydrates, then fats, and then proteins. 

Carbohydrates are like the "standard currency" for cells in terms of energy production. Carbohydrates also have a limited storage capacity in our bodies (about 1-2 days), therefore giving them first preference in terms of immediate usage. Fats are the secondary energy source when there is limited availability of carbohydrates, or if the energy needs at a current moment exceeds that provided by carbs. Fats also have a greater storage capacity in our bodies, hence the ease of fat gain and why fat stays on our body for long periods of time.


Interlude: Two Scenarios Involving A Calorie Deficit

Let's consider two scenarios: 

Scenario A: you decrease your caloric intake by decreasing food consumption

Scenario B: you increase your activity output.

The effect of taking either one of these actions is the creation of a negative energy (caloric) balance, since your caloric input is now below your caloric output. As explained earlier, negative caloric net balance = caloric deficit.

With Scenario A, reduced calories from external sources (meaning less food entering your mouth) to upkeep your body's current calorie requirements has the side effect of increasing glucose consumption, as the body must now increase usage of whatever immediate glucose is available in the blood for energy to compensate for this caloric deficit. A caloric deficit by diet is the most common way of creating a caloric deficit. However, the adverse effects of continuously being in a caloric deficit for long periods of times is discussed in Calorie Cycling: Using It To Effectively Build Muscle And Burn Fat.

With Scenario B, increased activity (for example by a combination of strength training and cardio) also causes an increase in glucose consumption. Be mindful that when creating a caloric deficit via exercise, the intensity of the activities must be such that you are burning more than you are eating. For example: if Alex decides to eat at his caloric maintenance requirements of 2500 calories daily, his overall energy output (energy burned) must be greater to cause the necessary negative caloric net balance.

My best advice is to MIX IT UP. For some days, create a caloric deficit via diet. Other days, create a caloric deficit via exercise. And yet for other days (especially rest days) eat at maintenance. Refer to Calorie Cycling: Using It To Effectively Build Muscle And Burn Fat.


The Food We Eat, Part 2: Backup Reserves And Getting To The Fat

With limited availability of glucose to perform normal biological functions and to maintain normal daily activity, the body responds to this caloric deficit by initially breaking down glycogen (the stored glucose) into glucose for use as energy. This process is called glycogenolysis. As glycogen stores also become exhausted, or is unable to meet the required energy demands, the body begins breaking down fat stores into fatty acids and glycerol. This process is called lipolysis. The body can then directly use fatty acids as energy or convert the fatty acids into glucose for energy. This process is called gluconeogenesis. Glycerol is used in combination of glucose to further break down glucose. This process is called glycolysis.

Proteins are rarely catabolized for energy UNLESS there is a scarcity of both carbohydrates and fats in your diet or system. While carbohydrates and fats are used as energy sources, proteins- the building blocks of the body- are more essential for repair and maintenance of tissue, muscle building, hormone and enzyme production, and other critical biological processes. With this in consideration, protein is not something the body will utilize for energy unless in critical conditions (e.g., extreme dieting or starvation). The last thing you would want is to lose your precious muscle mass!


Conclusion: The Necessity Of A Caloric Deficit For Fat Loss

And this is why a caloric deficit is essential: to exhaust as much fat stores as possible. A calorie deficit brings your body into the optimum state where the body, due to a negative caloric net balance, resorts to a dependency on its stored energy reserves and begins preferably tapping into the stored carbohydrates & fat. Carbohydrate-based energy sources are eventually exhausted to the point where fat-based energy sources can then be used, releasing the fat mass stored in your fat cells.

This is one of the many reasons why some diet plans consist of minimizing your overall carbohydrate intake, in an effort to coax this fat-release response by the body. You also need to understand that carbohydrate restriction is an indirect method of creating a caloric deficit, since you are basically reducing the primary energy source of the human body, and forcing your body to rely on the oxidation (burning) of its fat. Increasing glucose and glycogen depletion in order to catabolize fat stores can also be achieved by increasing caloric output: exercise.

Once caloric input is lower than caloric output, there is less energy from external food sources, and the desired effect of creating a caloric deficit will be achieved. You can have your cake and eat it... in moderation.

Always remember this: if there is no caloric deficit- whether you are eating at maintenance or eating at surplus- the body will rarely ever resort to burning your energy reserves. The fat will stay!

I hope that you see the role of how the food you eat- how it is used for immediate energy, stored, and released from stores- the energy balance and why you need a caloric deficit is a lot more clearer. The next part of the series talks about calorie counting and estimates for maintenance and deficits.

Thanks for reading!

References

1. How the Body Uses Carbohydrates, Proteins, and Fats
http://www.diabetesforecast.org/2011/mar/how-the-body-uses-carbohydrates-proteins-and-fats.html

2. The Catabolism of Fats and Proteins for Energy

http://antranik.org/the-catabolism-of-fats-and-proteins-for-energy/