July 08, 2020

Understanding Fats and Fat Metabolism

The concept of “Fats” is one of the most misunderstood concepts in fitness not only for new clients but also for most people in general.

We often hear in casual conversations about the desire to lose fat when what is really meant was to lose weight.

Notice how some people consciously choose non-fat or low-fat food product variants just to avoid that extra calories from fat while totally oblivious to the effects of that choice on the other components of their diets.

So, in these scenarios, it seems that to most people “Fats” are the villains and the usual culprit when one gains weight.

But this is far from the truth.

As most of you might already know, fat is an essential macronutrient of our body which gives us energy and allows our body to absorb vitamins.

But what else do we need to know about fats?

  • It is a necessary component of a healthy diet.
  • It is a part of every cell in our body.
  • It makes up about 60 percent of the brain.
  • Dietary fat is essential in the absorption of fat-soluble vitamins A, D, E and K 
  • It forms part of hormones that regulate important bodily functions such cytokines which are responsible for sending messages between cells, angiotensin which is involved in blood pressure control, and plasminogenwhich is vital in clotting of blood, to name a few. 
  • Generally, as an integral part of lipids, fats play an important role in digestion of food and insulation of our body by keeping our internal temperature regular.
  • It is a major source of our body’s energy.
  • It also functions as our body’s energy reserve.

If fat does all these good things for our body, then why do we want to lose it???

Well, what we want to lose are the excess fats that makes our body unhealthy.

Each person has a different story. There are some medical and genetic conditions which contribute to the excessive increase of fats in the body but based from my experience in this field, the confluence of these two factors generally has the most impact in prospective clients

  • Unbalanced dietwhich include uninformed or unguided food choices, and
  • Sedentary to Low-activity lifestyle.

What to do to keep the excess fats off and maintain the right levels of fats?

One of the keys to understanding how body fat works is to learn how our body processes the fat that we eat.

This process is called Fat Metabolism.

It is essential to have a working knowledge of how fat metabolism works to:

  • Keep us informed on how fat reacts in our body from the moment we eat until our body either burns or stores the fat.
  • Learn how certain fats react differently during the metabolic process thereby prompting us to take a closer look on the fats (and food in general) that we choose to eat.
  • Learn in the process the other factors that affect the movement of fats in our body which ultimately determine why some fats are burned while others remain stored, and cumulatively become the excess fat that we intend to lose.

This eagerness and drive to know the science coupled with an in-depth one-on-one consultation about your current fitness and eating habits will hit the ground running not only toward fat loss but more importantly your overall health goals and well-being.

So, what is Fat Metabolism?

According to the Journal of Childhood Obesity, fat metabolism is a biological metabolic process that breaks down ingested fats, which are mostly triglycerides, into fatty acids and glycerol.

It is then further broken down into simpler compounds that goes to our tissues such as the liver, heart, adipose or skeletal muscle. These compounds ultimately get processed to produce energy to the cells which we use for our bodily functions or get stored if there is a surplus from other sources of energy.

Essentially fat metabolism is the journey of dietary fat from ingestion until it undergoes either Beta-Oxidation(process of burning of fat and releasing of energy) or Storage in the adipose cell(as energy reserve). 

What are the stages in Fat Metabolism?

Dietary fats traverse this path:

  • Ingestion
  • Digestion
  • Absorption
  • Transportation
  • Beta Oxidation or Storage in the Adipocyte
  1. Fat Ingestion

     This is the stage when fat enters our body through our mouth from the food that we eat. Each food item that we consume contains certain amounts carbohydrates, protein and fats which would undergo their respective metabolic process once ingested.

Most dietary fats are in the form of triglycerides which accounts for 95 percent of all dietary fats (Baker Heart and Diabetes Institute, 2014).

  1. Fat Digestion

      This stage commences once the saliva starts to breakdown the food through chewing. The food then travels to the esophagus toward the stomach where it is digested into components, including triglycerides as fats.

      Next stop would be the small intestines where most of the digestion of fats happen. However, since the environment in the small intestines is aqueous or watery and fats, as you know, do not mix with water, our body makes a way for fats to travel by using bile salts as emulsifier to form fat globules.These fat globules are just like the circles that you see when you pour oil into water.

So, think of fat globules as triglycerides’ bubble carriers so that they can pass through the first part of the water slides of the small intestines.

Upon reaching lower part of the small intestines, the fat globules encounter bile salts from the liver which breaks down these fat globules into smaller droplets. This degradation into droplets will allow the potent pancreatic lipase to efficiently break down the triglycerides through hydrolysis(elements of water are added to rupture a chemical bond) into separate fatty acids and monoglycerides.

  1. Fat Absorption

Fat absorption happens in theenterocytes or the intestinal absorptive cells still in the small intestines.

At this stage, the fat droplets which served as shuttle of the fat in the watery environment of the small intestine were destroyed by the pancreatic lipase. To continue with the journey, the broken-down components of fats would need another shuttle to transport them to their next destination.

For this purpose, the individual fatty acids, monoglycerides and cholesterol would aggregate into structures called micelles. Micelles are roughly spherical structures which have hydrophobic interior (conducive to fat) and hydrophilic (or water-loving) exterior which would allow them to drift through the watery environment of the intestinal lumen and reach the enterocytes for absorption.

The micelles would release the fatty acids and monoglycerides into the enterocyte. Here, the fatty acids and monoglyceride will recombine into triglycerides and thereafter be packaged with cholesterol into bigger particles called the chylomicronsfor transportation into the bloodstream.


  1. Fat Transportation from Small Intestines to the Bloodstream

Again, due to the hydrophobic (repels water) nature of triglycerides and cholesterols, they require special transport proteins known as lipoproteins. These chylomicrons are one sub-group of lipoproteins which carry the digested fats from small intestine to the rest of the body. 

As the chylomicrons leave the enterocytes, the normal route would have been through the endothelial cells which form the barrier between vessels and tissues. But because chylomicrons are too large to pass through these endothelial cells, chylomicrons would enter a nearby lymphatic capillary called lacteal.

The chylomicrons would then glide in lacteal and flow into the thoracic duct then be dropped into the blood.

Once in the blood, the chylomicron releases fatty acids and monoglycerides in peripheral tissues like muscle (which use them for energy) or adipose tissue (for storage).


  1. Fat Beta Oxidation or Fat Storage in the Adipocytes

The fats released in the blood would then face either of these two fates: (1) undergo beta oxidation in the muscle tissue to produce energy or (2) Storagein the adipose cells for future use.

  1. Beta Oxidation

 It is a series of metabolic processes involving fatty acids that ultimately produce Adenosine Triphosphate (ATP)which is the energy currency of our body.

For fatty acids to be oxidized, they must be transported into the cell's mitochondria. The mitochondrion is an organelle that functions like a cellular power plant. It processes fatty acids (and other fuels) to create a readily usable energy currency (ATP) to meet the energy needs of the muscle cell. Most fatty acids are transported into the mitochondria using a shuttle system called the carnitine shuttle (Holloway et al. 2008 cited in Deyle, et.al, 2014).


  1. Storage

In cases where there is excess energy (there is abundance of energy from other sources such as carbohydrates), free fatty acids are generated and stored as triglycerides in the fat storage cell called adipocytesinstead of being oxidized in the muscles.

However, during low energy levels such as fasting or during exercise when other sources of energy is expended, lipolysis in the adipocytes occurs which breaks down triglycerides and releases free fatty acids to produce energy.                 

Insulin and Fat Metabolism

The abundance of insulin in the body serves as one of the major factors that affect fat metabolism.

This is because insulin is a key player in the control of our metabolic processes. It portrays a huge part in organizing the use of fuels for either storage or oxidation. Through these activities, insulin has profound effects on both carbohydrate and lipid metabolism, and significant influences on protein and mineral metabolism. 

One of the more notable effects of insulin in fat metabolism is that it inhibits breakdown of fat in adipose tissue.

This happens because insulin facilitates entry of glucose into adipocytes to synthesize glycerol. This glycerol, along with the fatty acids delivered from the liver, are used to synthesize triglyceride within the adipocyte thus further accumulating triglycerides in the fat cells. 

Because insulin also drives most cells to preferentially oxidize carbohydrates instead of fatty acids for energy, it indirectly stimulates the accumulation of fat in adipose tissue (VIVO Pathophysiology, 2019) especially when the stored fats are kept unused before another cycle of macronutrient intake occurs.

How does this affect us? Let us Examine Fed State vs. Starved State

  • Fed State happens when we have just taken our meal. This fed condition leads to the secretion of insulin,which as I have mentioned- one of the two most important regulators of fuel metabolism, the other regulator being glucagon.

When your blood has high concentration of glucose for a sufficient period, your pancreas secretes insulin. This action tells your cells to take in glucose instead of the other fuels such as fat, and put it in the most accessible fuel storage in the form of glycogen.

While the body is temporarily storing glycogen, it keeps everything else (including fats in adipocytes) in long-term storage.

  • Starved State, on the other hand, happens several hours after we eat a meal when blood glucose levels begin to drop. This leads to a decrease in insulin secretion and a rise in glucagon secretion.

Just as insulin signals the fed state, glucagon signals the starved state. It serves to mobilize glycogen stores when there is no dietary intake of glucose (Berg, et.al, 2002).

Once the glycogen bank becomes depleted, the body would then begin to process the other stored fuels such as fats or triglycerides in the adipocytes to generate ATP and use it for energy.

So, what does this have to do with Fat Loss?

Now that we know the science, here are some key takeaways:

  • Fat storage would only be tapped as energy source once glycogen levels in the body have already been depleted. So, there will be no fat oxidation or lipolysis that would happen unless and until the body has ran out of glycogen because it is the body’s first tier energy source.
  • A lesser glucose intake (which produces insulin that stacks glycogen) coupled with increased exercise levels will contribute greatly for the body to reach a starved state signaling the use of stored fats and thereby losing the fats in the process
  • Knowing that the food we eat really trigger our bodily processes just like how the body prioritizes the oxidation of carbohydrates when insulin is abundant, suggests that we should not take our diet lightly any longer.We should not eat just for sustenance’s sake. We should choose the right kind and amount of food that fits our body needs and lifestyle. 

You need to work with an expert on how to craft a diet and fitness regimen that would regulate these biological factors toward becoming fitter and healthier would be a greater feat than mere fat loss just like my client Anders below.

If you want to book you strategy session to discuss how myself or the CJ Coaching team can help please complete the application on the link here and book your call with me and the team!

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  1. Berg, J.M., et.al. 2002. Biochemistry. New York: W H Freeman.


  1. Bowen, R. 2019. Absorption of Lipids.VIVO Pathophysiology. Colorado State



  1. Bowen, R. 2019. Physiologic Effects of Insulin.VIVO Pathophysiology. Colorado State



  1. Clifford, J., et. al. 2017. Dietary Fat and Cholesterol. Colorado State University



  1. Deyle, M., et. al. 2014, The Physiology of Fat Loss.University of New Mexico.


  1. Journal of Childhood Obesity








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