Lipids are a broad group of naturally occurring molecules that include triglycerides or fats, phospholipids or emulsifiers, and sterols. As its name suggests, cholesterol is a sterol. Sterols have similar chemical structures, consisting of multiple rings and a side chain, and their functions involve sending chemical messages in the body. Consuming too much or too little fat causes ill health, and in a society with an abundant food supply, people tend to consume more than enough fat and cholesterol.
According to the American Heart Association, cholesterol is a fat-like substance essential to life and found in many tissues such as the brain and nervous system, as well as in every cell of the body. It stabilizes and strengthens cell membranes. As part of a healthy body cholesterol is used to make other sterols including vitamin D, bile acids, adrenal hormones such as cortisol, and sex hormones such as testosterone.
The body not only makes enough cholesterol from carbohydrate, protein and fat to meet its needs, but also gets it from foods of animal origin. Meats, fish, shellfish and poultry contain cholesterol. And meat products including whole and reduced-fat milk, cheese and eggs contain cholesterol. Plant-based foods such as fruits and vegetables, grains, nuts and seeds do not contain cholesterol.
Why Limit Lipids
When too much cholesterol is in the blood it becomes a health risk. Cholesterol can form deposits on the walls of arteries. These deposits can lead to atherosclerosis. The process begins with fatty streaks in the arteries. Then blood clots form along these injuries. When plaque and blood clots restrict blood flow, blood pressure rises. The higher blood pressure creates further damage until eventually a blood clot may block the flow of blood and cause heart attack or stroke.
The USDA Dietary Guidelines for Americans recommends intake of less than 300 mg per day of dietary cholesterol. To limit lipids in the diet, reduce total fat, saturated fat and cholesterol. An egg contains over 200 mg of cholesterol in the yolk. Limiting saturated fat can also affect total cholesterol. The USDA MyPyramid recommends a healthy diet low in saturated fat and cholesterol.
A fasting blood lipid profile provides a measure of various lipids in the blood including total cholesterol, HDL and LDL. HDL, or high density lipoprotein, carries cholesterol back to the liver to be recycled or disposed of as waste. High HDL protects the heart by helping remove cholesterol from circulation. LDL carries cholesterol to every cell of the body to meet its needs. But high LDL indicates potential harmful effects in the body due to an excess of cholesterol.
Recommendations of the National Heart, Lung and Blood Institute are to keep total cholesterol below 200 mg/dL of blood as a desirable level. Other levels include borderline high, or 200 mg to 239 mg/dL, and high, or above 240 mg/dL. HDL below 40 mg/dL of blood is considered low, and above 60 mg/dL is considered high. An optimal LDL level is less than 100 mg/dL, near optimal is 100 mg to 129 mg/dL, borderline high is 130 mg to 159 mg/dL, high is 160 mg to 189 mg/dL, and very high is above 190 mg/dL.