In technical biochemistry terms, lipids are molecular organic compounds, composed largely of carbon and hydrogen, that are essential for cell growth. Lipids are non-soluble in water and combine with carbohydrates and proteins to form the majority of all plant and animal cells. Lipids are more commonly synonymous with the word "fats" when speaking in terms of personal health, and though all fats are lipids, not all lipids are fats.

The three major purposes of lipids are energy storage, cell membrane development, and serving as a component to hormones and vitamins in the body. In healthcare, physicians order lipid tests or lipid profiles to measure cholesterol and triglycerides in a person's blood. Lipoprotein is the medical term used to define a combination of fat and protein.

Cholesterol is a naturally occurring substance in the body and is comprised of lipids. Cholesterol is separated into two types, high-density lipoprotein (HDL) and low-density lipoprotein (LDL). In a lipid test, the lipoproteins are separated so the level of each can be measured. Lipid tests are often part of preventative routine care, as they help determine whether there is significant risk for artherosclerosis, a hardening of the arteries that interferes with or interrupts blood flow. Lipoprotein levels are measured and dietary changes are usually in order when total cholesterol levels approach or rise above 200 milligrams per deciliter in the blood.

Fatty acids, also comprised of lipids, are an important dietary concern. Some fatty acids are essential and others are harmful. Fatty acids are categorized as mono-saturated, mono-unsaturated and poly-unsaturated.

Saturated fats come from animal sources such as milk, butter, and meats; and raise cholesterol levels in the blood. Unsaturated fats are of vegetable origin and decrease blood cholesterol. Sources of essential fatty acids include fish and beans. Vegetables, grains, and nuts are also considered an essential part of a cholesterol-lowering diet.