Is Fat Loss Wrecking Your Metabolism ? (Part 1)

What Is Your Metabolism ?

Your metabolism is a compilation of chemical reactions that take place inside our cells that either build up or break down molecules inside the body.

When molecules are broken down they give off energy, while when a molecule is built up it makes energy. The breaking down process is known as catabolism, while the building up is anabolism. 

These catabolic and anabolic reactions of the metabolism keep us alive also give us the energy to breathe, keep our bodies warm, move, grow and repair and think!

To make sure that our cells stay healthy and work properly thousands of different metabolic reactions take place each moment that  are regulated by the body.

The three components that make up your metabolism and control your energy requirements are: Basal Metabolic Rate (BMR), Thermic Effect of Activity (TEA) which comprises a few different forms of movement  and Thermic Effect Of Food (TEF). Let’s take a closer look at each one.

Basal Metabolic Rate (BMR)

The amount of calories (energy) your body requires to keep you alive is your Basal Metabolic Rate (BMR). This accounts for upwards of 60% of your total caloric needs in a day.

Whether you did a triathlon or sat on the couch the entire day this calorie requirement stays the same, however you can change your BMR. 

The amount of muscle mass that you have is directly correlated with your BMR. More muscle mass means that your BMR will be elevated to a greater calorie requirement.

Anything that decreases muscle mass such as dieting will also decrease BMR. This  means it is very important to preserve muscle mass when losing fat so we can keep BMR as high as possible and burn more calories… just sitting there on the couch!

Thermic Effect Of Activity (TEA)

Because you are doing more than just laying in bed all day long you are going to require more calories than just your BMR  to provide energy for daily activities.

The thermic effect of activity is all the calories expended on a daily basis through formalized exercise combined with you non exercise activity thermogenesis (NEAT). 

NEAT accounts for the calories we require for activities that are not sleeping, eating or exercising.

These kind of tasks would include: walking to work, yard work, typing or using a standing desk at work. Something as simple as fidgeting or adjusting your position all fall underneath the NEAT umbrella.

Very interestingly NEAT expenditure is regulated by changes in energy balance (calories coming in) and will decrease when dieting, but be boosted by short periods of overfeeding.

Thermic Effect of Food (TEF)

This is the amount of calories you require to digest, break down and absorb all the food you eat. Eating does temporarily raise your metabolism because the body is working to turn your food into energy for your cells.

This short lived boost in metabolic function takes place once you are eating and peaks roughly three hours after the meal is finished. All the different macronutrients actually require a different amount of calories to be digested.

We Now Know Better

The Thermic effect of food was the basis for the theory that smaller more frequent meals lead to greater fat loss.  

The theory was the more often you ate the more TEF would be elevated and more  calories would be burned as a result.

However we have discovered that it doesn’t matter how frequently you eat meals, but the overall caloric content and macronutrient breakdown that contributes to TEF.

Each macronutrient actually boosts the metabolism by a different amount: Fats 3-4%, Carbs 6-8% and Protein 25-30%. Spicy foods also have an impact on the TEF as well.

The Thrifty Metabolism

When most people lose fat  their body weight  goes down, as will the number of calories they burn at rest (BMR) and during their daily activities (NEAT).

The reason BMR  will slow down with weight loss is because there’s less body weight to support, which means even at rest the body doesn’t have to burn as many calories

The reason NEAT slows down is because your body requires less energy to support your daily movement now that you are smaller.

NEAT will also decrease because as the metabolism gets thrifty it realizes that it can’t afford to burn the extra calories on movement. Even if you move the same amount it will burn fewer calories.

The body is highly adaptable and knows if less is coming in, we need to make sure less is going out. We have a specific gland  that helps to control our metabolic rate named the thyroid.

Thyroid and Leptin

The thyroid is a very complicated, and important gland in the body that controls our metabolic rate.

Leptin is a hormone secreted from our fat cells, the more fat you have the more leptin you have circulating letting the brain know we have enough stored energy. Ithelps to increase or decrease our metabolic rate by delivering a report on how much energy we have available to the brain.

That energy report is sent to the thyroid to make any necessary adjustments based on available energy. The thyroid will increase or decrease the metabolism based on the amount of leptin.

When someone is in a caloric deficit, and has lost a significant amount of fat there is far less leptin.

Too little leptin signals to the body that there is far less energy available and the metabolic rate needs to be slowed down to stay in balance. On the other side the body will increase appetite to get more energy into the body. 

As a result the metabolism being slowed down you will burn far fewer calories at rest, and  when exercising or doing non exercise activity. When the metabolism stays in this condition for long enough it starts to slow other areas of the body down as well.  

Common symptoms of someone who has dieted for too long include fatigue, fat loss plateaus, decreased libido, worse body composition and getting cold easily, constipation. Many of these can be tied directly back to the thyroid.

Now that you have a far better understanding of what your metabolism is and how losing fat can actually slow it down we will be cover tactics in the second part of this blog series on how to lose fat without slowing down your metabolism. Stay Tuned!

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