FAT AND CHOLESTEROL: Fuel, Function, Facts and Fiction
What are lipids like fat and cholesterol?
In general, lipids are a special class molecules whose most outstanding feature is water-insolubility. The predominant lipids in our body and diet are triglycerides (fat) and cholesterol. Because of their inability to dissolve into water, we must bend over backwards, so to speak, to accommodate them both during digestion and also inside of our body. During digestion, an emulsifying substance called bile is employed to facilitate lipid digestion and absorption. As for fat and cholesterol inside of our body, they require special transport shuttles to circulate. Let's not forget that fat also has its own cell type specifically designed for storage. These cells are called adipocytes or fat cells and large collections of adipocytes are called adipose tissue. Adipose tissue is found under our skin (subcutaneous fat) and in deeper deposits such as in the abdomen.
What is the difference between fat, oils and triglycerides?
Fats and oils are common terms for triglycerides. Often fat and oil are considered to be different based on appearance; fat being more solid at room temperature and oil being more liquid. However, they are really two of the same thing in general. They are both large collections of triglycerides. A triglyceride molecule is a combination of three fatty acids linked to a glycerol molecule backbone (see Figure “A”). While a triglyceride molecule will always have this general design, there can be phenomenal variability to the fatty acids that link to glycerol. Meanwhile, phospholipids are a diglyceride that have a phosphate attached in the 3rd position instead of a fatty acids (see Figure “B”). Moreover, phospholipids tend to have an additional molecule attached to the phosphate like choline which collectively is called phosphatidylcholine (or “lecithin”). Phospholipids are important components of cell membranes.
What is cholesterol and can we make it in our body?
Perhaps no other substance in foods or in our body receives more bad press than cholesterol. However, it is important to realize that cholesterol is absolutely vital to our existence. Cholesterol can be made in many of our cells and under normal situations we seem to make all that we need. In fact we will make about 1 gram of cholesterol per day. Our liver is by far our most productive organ when it comes to making cholesterol. Cholesterol is a necessary component of cell membranes and many vital substances in our body are made from cholesterol. These substances include bile components, vitamin D, testosterone, estrogens, aldosterone, progesterone, and cortisol. In more recent years we have expanded our understanding of what foods and factors really increase blood cholesterol levels and it now seems clearer that excessive energy intake, with more from carbohydrate and higher levels of body fat that seems to drive cholesterol up in the blood more so than cholesterol containing animal foods independently.