Fats and oils are important elements of our diet. Several foods naturally contain fats and oils, or we add them during the preparation of foods. The types of fats and oils we consume vary, and while some are beneficial to us, others can be harmful if consumed in excess.
The purpose of this blog is to discuss a component found in fats and oils – cholesterol.
Putting lipids, fats and oils, and cholesterol in perspective
Fats and oils in our diet are composed of insoluble organic compounds known as lipids. The three main types of lipids found in fats and oils are triacylglycerols, phospholipids, and sterols. Let us briefly touch upon them.
Triglycerides. Over 95 percent of dietary fats are composed of triglycerides (a.k.a. triacylglycerols). Our body’s energy is primarily provided by carbohydrates in the short term, but triglycerides stored in fat cells meet our long-term energy needs.
Dietary fats contain a small amount of phospholipids. A phospholipid is a crucial component of the membrane that surrounds each cell in our body. Phospholipids also form structures in which fats are enclosed and transported throughout the body.
The third type of lipid is sterol. Cholesterol is perhaps the best well-known sterol. In addition to being an important component of the cell membrane, cholesterol is needed for producing sex hormones and vitamin D3 as well as making bile salts to aid digestion. This blog discusses cholesterol in detail.
The above discussion helps us understand what lipids are and how cholesterol fits into the picture. Be aware, however, that the body receives cholesterol not only from diet but most of it is synthesized within our bodies as well. More on this later.
Cholesterol: Sources and their movement path within our body
As mentioned above, there are two sources of cholesterol in our body.
The liver produces all the cholesterol the body needs to make essential substances like hormones and bile acids. The liver makes about 70% of the cholesterol present in blood. 30% of the cholesterol comes from animal-based foods.
After cholesterol is synthesized within the body or is acquired through diet, it must be transported to various tissue cells for the purposes outlined before.
Cholesterol does not dissolve in water or blood. Hence cholesterol is packaged in tiny, protein-covered particles called lipoproteins and transported within the body. Lipoproteins carry cholesterol along with other components such as triglycerides, phospholipids, vitamins, and proteins that need to be distributed to distant cells.
This enables the tissue cells to absorb cholesterol according to their needs and return the excess cholesterol to the liver for recycling. Hence cholesterol circulates in our bloodstream to meet the needs of tissue cells. The liver also converts cholesterol into bile acids and excretes some of it from the body. This is how cholesterol is processed within the body.
The lipoproteins, which transport cholesterol, are of two types – Low-Density Lipoprotein (LDL) and High-Density Lipoprotein (HDL).
LDL carries more fats than proteins whereas HDL carries more proteins than fats and is denser than LDL.
Let us now explore why HDL is so much better than LDL and cholesterol’s role in all this.
Why does cholesterol have such a bad reputation?
Now we know that cholesterol is transported packaged within lipoproteins, which are of two types, HDL and LDL. We also know that LDL carries more fats whereas HDL carries more proteins.
To add to the above, each lipoprotein is enwrapped by one or more large molecules called apolipoprotein to provide structure, stability, and solubility to the lipoprotein particle.
HDL particle is enwrapped by apolipoprotein A (apoA in short) whereas LDL particle is enwrapped by apolipoprotein B (apoB in short). In fact many low-density lipoproteins including VLDL, IDL, and LDL carry this apoB signature.
Now, this is how cholesterol gets its bad reputation.
As we discussed before, the transport of cholesterol to different tissues and cells of the body is dependent on LDL (accompanied by apoB apolipoprotein). Hence, we will have a higher concentration of LDL and apoB in our body as cholesterol levels increase in our blood.
However, high levels of LDL in the blood are known to form plaque that narrows blood vessels and causes heart disease by sticking to the blood vessel lining. Smoking and high blood pressure further damage the blood vessels, resulting in a greater retention of LDL and an acceleration of atherosclerosis.
Conversely, HDL removes cholesterol from the bloodstream, from LDL, and artery walls and transports it back to the liver for recycling. It attempts to undo the damage caused by LDL.
Therefore, cholesterol alone does not damage the blood vessels. The LDL particles and the accompanying apoB damage the blood vessels first, allowing cholesterol to stick to the damaged blood vessels and do further damage.
Because of these reasons, LDL is considered bad “cholesterol” for health since it triggers atherosclerosis, while HDL neutralizes the effects of LDL. We are more likely to prevent heart disease and other chronic conditions if we have lower LDL and higher HDL.
What are the reasons for increased cholesterol levels?
We read before that high levels of cholesterol result in high concentrations of LDL and apoB which are responsible for atherosclerosis. The question now arises what causes high levels of cholesterol?
Many people believe that eating foods containing cholesterol leads to high cholesterol levels. This is not entirely correct. If the dietary intake of cholesterol is too high, it is simply converted into bile salts or excreted from the body.
Studies have shown that the amount of dietary cholesterol does not significantly affect cholesterol levels in our body. The biggest influence on blood cholesterol levels is the mix of fats and carbohydrates in our diet—not the amount of cholesterol we eat from food. Eating lots of saturated or trans fats can cause the liver to produce excess cholesterol and increase levels of atherosclerosis-causing lipoproteins in our blood.
Further, insulin resistance—when cells no longer respond appropriately to insulin— can disturb the lipid profile of a person. It can cause low HDL and high LDL.
Thus, avoiding diabetes and carefully selecting fats are essential for maintaining a healthy lipid profile.
How to control cholesterol with diet?
The risk of high cholesterol increases when there is a high level of circulating fat, which is caused by inactivity, obesity, fatty diets, and alcohol consumption. The diet plays a crucial role in cholesterol accumulation.
For a healthy cholesterol level, one should choose foods that contain monounsaturated and polyunsaturated fats, like nuts, fish, chia seeds, flax seeds, olives, macadamia nuts, avocados, extra virgin olive oil, sesame oil, and mustard oil.
Trans and saturated fats raise cholesterol levels in the liver, so they should be avoided.
Furthermore, a high-fiber diet reduces cholesterol absorption in the body. Fruits, vegetables, and oats are rich in fiber, which prevents cholesterol from being absorbed.
Wheat, brown rice, oats, rye, barley, buckwheat, quinoa, corn, and rice are widely recognized as sources of dietary fiber. They also contain high levels of antioxidants, which can effectively fight free radicals and reduce LDL cholesterol damage or oxidation, which may result in atherosclerosis and inflammation of the arteries.
Eating foods rich in soluble fiber such as isabgol, black beans, lima beans, kidney beans, brussel sprouts, sweet potatoes, broccoli, turnips, carrots, avocados, pears, figs, apricots, apples, guavas, various nuts and seeds, and whole grains help to reduce total cholesterol.
Summary
We need cholesterol to function properly in our bodies, but high levels of cholesterol in our blood can cause serious health problems.
Our liver produces cholesterol in our bodies, but diets high in saturated fats and trans fats cause it to produce excessive amounts. The amount of harmful cholesterol in our body may also be affected by our metabolic health. Therefore, we should consume foods containing the above-mentioned fats in moderation and maintain a healthy metabolic rate.