Monday, January 11, 2010

Fatty acid and Cholesterol Digestion

Here is my answer to a question proposed to me by a fellow low carber;

Dr. Jim,

You explain quite often how carbohydrates and sugar (whoops, they are both the same!) are processed in the human body. Could you explain how dietary fat and cholesterol are processed in the body?

Also, is Ultimate Wellness still on the air? I hope the link did not change.

Thank you for all that you are doing to promote proper nutrition!

My response;

Hi there!

First off, yes Ultimate Wellness! is still on the air, but the format has changed. It is now a free subscription and the segments are much shorter, 6-8 minutes to be precise. There will be about 1-3 videos per week. Go to to subscribe and watch the first video. As always feedback is greatly appreciated!

Yes, I do talk alot about carbohydrate digestion, so lets talk a little bit about fat and cholesterol digestion :-)

Fats are found as triglycerides in most of the foods we eat. A triglyceride is simply 3 fatty acid molecules all linked to another molecule known as glycerol. So when we break down a triglyceride we wind up with 3 fatty acids and a glycerol molecule. The fatty acids can be used for the production of ATP or stored as fat, and this is all dependent upon how much sugar was consumed with the fat. If we eat alot of carbs with a fatty meal, the body will store not only the carbs as fat, but the triglycerides as well. If the fat is consumed with very little to no carbs, it will be utilized for the production of ATP, thus, it will not be stored. Notice how I am refraining from using words like 'burned for fuel' or other words which imply a combustion process.

Always remember, digestion is not a combustion process. It is a controlled process which creates our ultimate energy molecule, ATP, with the release of CO2 and O2 in the process. This is why the calorie is irrelevant. Calories are determined via a combustion process, not a digestive process, so it is ok to ignore them.

Now what happens with cholesterol in the foods we eat?

Cholesterol digestion is different as it is not digested in the true sense of the word, the molecule isn't broken down like carbs, fats or proteins; cholesterol is already in its most basic form. Remember that carbs are broken down into sugars (the most basic part), proteins are broken down into amino acids (its most basic part) and triglycerides are broken down into fatty acids and glycerol.

The cholesterol molecule will be encapsulated by bile acid pigments in the small intestine and transported to the liver where it can meet many fates. Since cholesterol is a type of fat, a sterol to be precise, it cannot be transported in our blood stream without a carrier molecule. This is because our blood is more of a watery (aqueous) environment and we all know that fat and water dont mix. Without these special carrier molecules, cholesterol would just all clump together (as would triglycerides which also need a carrier molecule, known as chylomicrons and VLDL) and it couldn't get anywhere in our body. The carrier molecules for cholesterol are referred to as the HDL, LDL and the lessor known IDL. Adding all of these carrier molecules together is how we derive our total cholesterol.

Now I stated that the fats in the foods we eat will either be stored or used for the production of ATP. So what happens to cholesterol after it gets to the liver? It can have many fates. It can either be carried out of the body via the stool; it can be used to create steroid hormones like estrogen, testosterone, progesterone, bile acid pigments or cortisol etc; it can be used to turn off the very enzymes that make cholesterol that is HMG Co-A; it can diffuse into the nucleus of the cell and attach to RNA, DNA and turn off the very creation of the enzymes that make cholesterol.

Another thing I have seen with increased cholesterol consumption is an increase in the amount of HDL circulating in the blood.

Hope this helps!

Thanks again for the questions!

dr jim


  1. If you eat oxidized cholesterol will it come out of the liver still oxidized?

  2. That was the clearest explanation of cholesterol metabolism I have read. You seem like a very reasoned and thoughtful dietary advisor. I am fortunate to have had a reasonably active life and a good diet. My cholesterol is never above 170 and the HDL to LDL is 110 to 60 on average. However, I am fond of lean meat as well as fresh vegetables. Would I benefit by eliminating meat from my diet?

  3. "That was the clearest explanation of cholesterol metabolism I have read."
    I should say: that was the ONLY clear explanation!