The Fat Series – how do we burn fat?

Today I’m looking at how the body can burn fat for energy, and the different types of fat in the body. It may get a bit sciencey… stick with it!

The main energy system in the body uses glucose (from carbohydrates) but I’m going to save that discussion for another time, and focus on the fat. As burning fat is not the body’s main source of energy, it is more complex for the body to do. You can train your body to become better at it, depending on what exercise you do and how you’re eating. I’ll discuss this in parts 3 and 4 of The Fat Series. Here, let’s just look at what it means to ‘burn’ fat.

The Army Girl's Guide to how the body burns fat

Your fat stores

Fat is stored in the body in cells, known as adipocytes. The fat in the cell is stored in the form of triaglycerol.  When you use fat for energy it is freed from the fat cell through a hormonal and enzymatic process. The fat cell is still there, ready to be filled with more fat when it becomes available. Much like a balloon deflating, when you lose fat the fat cells remain. We can never get rid of fat cells, but we can make more!

Releasing fat as free fatty acids to be used as energy is essentially ‘burning’ fat

When the fat cell is triggered by hormones, through enzymes, the triaglycerol is released into the blood stream as free fatty acids (FFAs), and they are transported to the place where the energy is required. (A note drawing on last week’s blog, this fat cell is not necessarily in the area that is requiring the energy. The FFAs get transported in the blood to the area – hence not spot reducing fat).

If you want to look further into the detail, check out the importance of the hormone lipase. And whilst you’re looking into it, check out the enzymes which help release the fat from the fat cells (hormone sensitive lipase – HSL) and the enzyme which helps get the FFAs inside the muscle cell for use as an energy source (lipoprotein lipase – LPL).

When your fat cells are empty, they shrink and give you a more lean appearance. This is why we like to burn fat!

Why your number of fat cells increase

It used to be said that you cannot change the number of fat cells in your body once you reach adulthood, and that only their size can change. However we now know that both size of cell, and number of cells can increase under certain conditions. These are:

  1. During late childhood and early puberty
  2. Throughout pregnancy
  3. In adulthood when extreme amounts of weight are gained.

Some people are genetically predisposed to have more fat cells than others and women have more fat cells than men (lucky us!). This is one reason why yoyo dieting is so bad for you; you can increase the number of fat cells you have, and then those fat cells are there ready and waiting to take in more fat!

Different types of fat

Not all fat is created equal. Fat is divided into two categories in the body: subcutaneous and visceral. Subcutaneous fat is the type that lies just underneath the skin and is soft to poke. Visceral fat lies deeper beneath the abdominal wall and can surround your internal organs. Around 90% of your fat is usually subcutaneous, and it’s the 10% visceral that is cause for concern. When it comes to fat… location matters!

Fat cells — particularly visceral fat cells — as we learnt above, are biologically active. The hormones secreted have a far reaching effect on other tissues, and can be linked to a variety of diseases.

Fat and disease

Subcutaneous fat produces a higher proportion of beneficial molecules, and visceral fat a higher proportion of molecules with potentially deleterious health effects. Visceral fat makes more of the proteins called cytokines, which can trigger low-level inflammation, a risk factor for heart disease and other chronic conditions. It also produces a precursor to angiotensin, a protein that causes blood vessels to constrict and blood pressure to rise.

Both fat stores are available to be used as energy. And because of the good blood flow to this visceral fat it means it’s ready and waiting to be used! Visceral fat is also more responsive to catecholamines (fight or flight hormones), which can help get fat burning underway.

Concerned about visceral fat?

Here’s a little test to see if visceral fat is something you should be concerned about:

If you have a waistline greater than 40 inches for men and 35 inches for women, according to the Journal of the American Medical Association, that’s an indicator that you are carrying too much belly fat, even if you’re a relatively healthy weight and generally in good health.

Grab a tape measure and wrap it around your waist at the level of your navel, just where the top of your hip intersect a vertical line down the body:

Where to measure for visceral fat

Don’t suck in your stomach or pull the tape tight enough to press into your skin:

Measure your visceral fat

There are ways we can reduce our visceral fat (and of course subcutaneous fat), and next week I’ll be looking at how you can use exercise to aid your fat loss journey. And in the final part of The Fat Series I look at how you can eat to burn fat!

See you next week!

If you didn’t see last week’s blog on spot reducing fat, then check it our here. And don’t forget to subscribe to my newsletter so you never miss all this juicy info, and also so you can access my members only free resource library.

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