Saturated Fat: What Really Happens When You Eat It.

Hint: It's not what you think

We've all read or heard at some point that it's important to cut down on our saturated fat intake to reduce our risk of heart disease and look after our liver.

'Saturated fat clogs the arteries, leading to heart disease'

'Saturated fat causes non-alcoholic fatty liver disease'

Even the NHS website regurgitates this rhetoric repeatedly, so today I want to look at the journey of dietary saturated fat through the body, to show you that it is the innocent visitor to a very elaborate party.

Where fat digestion starts

Most of the digestion (or breakdown) of saturated fat happens in the small intestine, when it binds to bile salts, and this emulsifies the fat droplets. These fat droplets are then broken down by pancreatic lipase, an enzyme, into smaller pieces (from triglycerides to monoglycerides and free fatty acids). These are then ready to be absorbed by specialised cells called enterocytes that line the intestines.

The cargo ship: A Chylomicron

Once inside these cells, the monoglycerides and free fatty acids reassemble the fat back into triglycerides (yes, bonkers I know). Fat doesn't dissolve in water and blood is 80% water, so this fat needs to board a large cargo ship called a chylomicron to sail the waves and get to its destination. This ship carries other cargo such as fat soluble vitamins A,D,E and K and cholesterol. See image below...

This ship doesn't enter the blood stream yet though, first it takes a one way ticket up the thoracic duct which is like a lymph superhighway. It's important to note that it does not sail anywhere near the liver and therefore it's fatty cargo does not contribute to a fatty liver.

The Chylomicron is NOT a cholesterol delivery ship

Once the ship gets to the top of the thoracic duct, it enters the bloodstream. As the ship sails around, it releases its cargo, mainly fat (triglycerides), to cells such as adipose tissue, muscle and heart. The heart LOVES fat! it's preferred energy source. Given the choice, it favours fat over glucose.

As the ship offloads, it gradually gets smaller and smaller in size, and is then called a chylomicron remnant. Remnant because it doesn't carry much cargo, mostly cholesterol and fat soluble vitamins. This is because it is a fat delivery ship, not a cholesterol delivery ship. This depleted ship now travels to the liver, and enters via a vast network of capillaries called hepatic sinusoids with its remaining cargo.

Your liver - Customs and Excise

The liver is an amazing organ and works as a regulatory checkpoint, a bit like customs:

-How much cargo do we store?

-Which cargo will be sent out again?

-What cargo needs to be detoxified?

-What cargo needs to be activated?

Each bit of cargo needs specialised handling.

In the case of cholesterol, it is so essential to life, that if the liver doesn't receive enough from the diet, then it will make it. In fact, it makes about 80% of the cholesterol that your body needs.

Your body needs cholesterol to:

1.Help Build Cells: 

Cholesterol is a building block for your cell membranes, the outer layers of your cells, keeping them stable and working properly.

2.Make Important Hormones: 

Your body uses cholesterol to make hormones like testosterone (which affects things like muscle and mood), oestrogen (important for reproduction), and cortisol (a stress hormone).

3.Help Digest Fat: 

Cholesterol is also used to make bile, which helps break down fats in your food so you can digest them.

4.Keep Nerves Working: 

Cholesterol is part of the covering around your nerves, helping them send messages through your body.

Cholesterol does not pass the blood brain barrier, but it is so essential to brain function that your brain also makes cholesterol.

The terms 'saturated fat' and 'cholesterol' are used interchangeably in the media, but they are quite different chemically. Whereas saturated fat is obviously a type of fat -clue is in the name. Fun fat: 'heart healthy' extra virgin olive oil is 14% saturated fat. Cholesterol is not a fat. It is a sterol, a waxy fatty-like molecule, with a completely different structure, that is essential for all of the above reasons and more.

How does eating saturated fat raise artery clogging cholesterol?

It doesn't! Remember that the dietary fat that you eat boards a chylomicron and this is a fat delivery system, not a cholesterol delivery system. As it's travelling through your veins and arteries, delivering fat to be stored in cells, it's not dumping essential cholesterol en route like some kind of dirty cargo. If you don't believe me, then now would be a good time to read 'If Cholesterol Clogs The Arteries, Then Why Isn't It A Major Component Of Arterial Plaque'

The confusion surrounding saturated fat, cholesterol, arterial plaque (clogged arteries) and fatty liver continues for numerous reasons that I'll go into in more depth in another post. It's far too long-winded. But for today I just wanted to explain the digestive route of dietary fat, so that you could understand that it is safe to eat, and your body is not working against you.

I hope this has helped?

Till next time,

Ali x

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