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Term	Description
L-carnitine	A nutrient (resembling amino acids used by the body to transport long-chain fatty acids to the mitochondria in the cells, where it is burned mainly for muscular energy. It can help prevent fatty buildups in the heart and liver. Deficiencies in L-carnitine can appear as low energy levels, muscular weakness, mental confusion, angina (heart pain) and weight gain. Vitamins B1, B6 and C; iron; and the amino acids lysine and methionine are needed for carnitine synthesis. carnitine is found in meats and other animal foods. Vegetarians may want to consider supplementation with L-carnitine.
Lactose	A disaccharide composed of glucose and galactose; commonly known as milk sugar.
Lactose intolerance	A condition in which an individual lacks the enzyme lactase that breaks down lactose so that it can be digested. Symptoms include bloating, gas, abdominal discomfort and diarrhea. Lactose intolerance differs from milk allergy, which is caused by an immune reaction to the protein in milk.
LDL (low-density lipoprotein)	LDL is a carrier molecule that transports cholesterol and triglycerides in the blood from the liver to the body's cells. A high level of LDL is associated with a high risk of heart attack because it indicates there is too much artery-clogging cholesterol in the blood. Although long considered the "bad" cholesterol, recent research indicates that some sub-fractions of LDL are actually heart protective.
Lecithin	A phospholipid widely distributed in animals and plants and the major component of cell membranes. It is important to normal cell function and has antioxidant properties. Sources of lecithin include eggs, dairy products and meats. It is also used as an emulsifying or wetting agent in food products.
Legume	Any plant in the bean and pea family in which the seed is enclosed in a pod, including chickpeas, lentils, soybeans, peanuts and many others.
Lignin	Also spelled as lignan, a non-carbohyrate plant component that is classified as fiver. It is abundant in flaxseed, which also contains essential fatty acids.
Lipid	A group of organic compounds that includes fats and oils. Examples of fatty substances in the blood include cholesterol, free fatty acids and trigylcerides.
Lipid profile	An analysis of the blood, usually including HDL (so-called "good" cholesterol), triglycerides, LDL (so -called "bad" cholesterol) and total cholesterol.
Lipolysis	The natural process of burning fat for energy. Fat can come from dietary sources or body fat.
Lipoprotein (a)	A subclass of LDL (low-density lipoprotein), a conjugated protein in which lipids form an integral part of the molecule. Lipoprotein (a) is particle for particle classified as larger, fluffier and more cholesterol-rich than lipoprotein (b), and therefore less of a risk for plaque formation on arteries. This means that lipoprotein (a) is less likely to increase risk factors for vascular disease.
Lipoprotein (b)	A subclass of LDL (low-density lipoprotein), a conjugated protein in which lipids form an integral part of the molecule. Lipoprotein (b) is particle for particle classified as smaller and denser than lipoprotein (a), and therefore more likely to increase plaque formation on the artery wall. This means that lipoprotein (b) is associated with a greater risk of vascular disease.
Lipoprotein profile	An analysis of the blood that looks at high and low-density lipoproteins (HDL and LDL). More detailed analyses include the subclasses of lipoprotein such as lipoproteins (A) and (B).
Lithium	An alkali metal used to treat psychological conditions such as bipolar disorder. As a maintenance therapy, it is useful in preventing or diminishing the frequency of relapses in bipolar manic-depressive patients. Contraindications include individuals who have severe cardiovascular or renal disease and those with evidence of severe debilitation or dehydration, sodium depletion, brain damage and any conditions requiring a low-sodium diet.
Liver	A large glandular organ located in the upper abdominal cavity, which secretes bile and is essential to metabolic processes.
Low blood sugar	See Hypoglycemia.
Lupus erythematosus	A chronic inflammatory disease that can affect many parts of the body, including skin, joints, kidneys, blood cells, heart and lungs. Episodes of lupus tend to come and go throughout life, and may cause an individual to feel tired and achy. But with treatment with cortico-steroid medication, topical steroids and anti-maleria drugs, patients can lead an active, healthy life. About 40 to 50 Americans out of every 100,000 have lupus, and most of them are women. There are several types of lupus, but systemic lupus erythematosus (SLE) is the most common and the type that causes the most difficulties. It can lead to problems ranging from fevers to sore muscles to anemia.
Lyme disease	An acute inflammatory infection transmitted by a deer tick. An early sign of an infection is the appearance of a red bull's-eye-shaped skin eruption at the site of the bite. Knees and other large joints are most commonly involved, with local inflammation and swelling. Flulike symptoms - chills, fever, headache and malaise - may be the first signs of infection and may precede the joint pain. Undiagnosed Lyme disease can lead to heart, nerve and other serious problems.