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Nutrition and Metabolism

Cholesterol

What is cholesterol?

Cholesterol is an essential lipid for normal cell function. It is used to form cell membranes, vitamin D, and steroid hormones.  Cholesterol exists in two major forms in the human body: LDL and HDL. LDL distributes cholesterol to different parts of the body and tends to accumulate on the surface of blood vessels at high concentrations.  Long term accumulation of LDL on blood vessels can cause many cardiovascular diseases such as atherosclerosis, stroke, and heart attacks. This has led to LDL cholesterol being known as the “bad cholesterol”. Cholesterol cannot be broken down in human body so excess cholesterol is transported by HDL to the liver where it is processed for recycling or fecal disposal.  As a result, HDL has the opposite effects as LDL and is often referred as the “good cholesterol”.

What is a normal cholesterol level?

Cholesterol is normally measured at three levels: Total cholesterol, LDL cholesterol and HDL cholesterol.  Their ranges are shown in the following table.

Types Range Remarks
Total Less than 200 mg/dL Desirable
200-239 mg/dL Borderline high
240 mg/dL or higher High
LDL Less than 129 mg/dL Desirable
130-159 mg/dL Borderline high
160 -189 mg/dL High
190 mg/dL or higher Very High
HDL Less than 40 mg/dL for men or 50 mg/dL for women Low
40-50 mg/dL for men and 50-59 mg/dL for women Average
60 mg/dL or higher for both men and women Desirable

What determines cholesterol level in human body?

The cholesterol level in the human body is determined by diet and genetic makeup.  Diet provides cholesterol or materials to make cholesterol while genetic makeup controls the efficiency of cholesterol synthesis and clearance.

What dietary factors influence cholesterol level in human body?

The human body is able to efficiently produce cholesterol from the metabolism of major nutrients.  On average, 75% of cholesterol in human body is synthesized by the liver and 25% comes directly from diet. Since dietary cholesterol will directly increase the level of LDL, it should be minimized unless you are a patient of cholesterol deficiency, a rare condition that needs prescription for cholesterol supplement. Most health organizations recommend consuming no more than 300mg of cholesterol daily. 

The liver’s cholesterol synthesis and cholesterol metabolism are greatly influenced by the types of fats in diet. Unsaturated fats increase HDL and decrease LDL and are therefore the “good fats”.  Saturated fats increase HDL, but also increase LDL making them the “bad fats”. Trans fats decrease HDL while increasing LDL and are therefore the “ugly fats”.

How does genetic makeup influence cholesterol levels in human body?

Many genes involved in cholesterol metabolism affect how your body reacts to certain food in making or disposing of cholesterol, the Apo E gene is one of them. As described in Apo E and Cholesterol Management, the APOE4 variant has a higher rate of LDL formation making carriers prone to high levels of LDL cholesterol.  In contrast, the APOE2 variant has a lower rate of LDL formation and the carriers normally have lower LDL cholesterol level. Due to the difference in LDL formation rate, APOE4 carriers are better suited to high-carb, low-fat diets while APOE2 carriers are better served by low-carb, high-fat diets. The APOE4 variant is quite common in human population, ranging in frequency from 10 to 30% occurrence among ethnic groups.

How to improve blood cholesterol levels?

Eat smart and eat according to your genetic makeup!

Limiting dietary cholesterol and the “bad and ugly” fats are the first step.  Plant derived foods do not contain cholesterol and tend to have less saturated and more unsaturated fat making them the best foods for lowing blood cholesterol.  Foods from animal sources are normally cholesterol-rich and tend to have more saturated and less unsaturated fat. These foods should be limited to prevent high blood cholesterol. Trans fats are abundant in junk foods and should be avoided whenever is possible.

Avoiding excess calories is another step.  Excess calories will be converted into saturated fat in human body so eating too much, even if the food is “healthy”, is equivalent to eating saturated fat!

Soluble fiber binds to cholesterol in human intestines and prevents it from being absorbed.  Therefore, dietary fibers have cholesterol lowing effect.  Fiber-rich foods are all from plant sources, including whole grains, beans, vegetables and fruits.

 

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