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Term	Description
Fainting	Characterized by sudden pallor, loss of consciousness and, occasionally, slight twitching or convulsive movements, fainting can be caused by any condition restricting blood flow to the brain.
Fasting	A period when no food and only water is consumed. Fasting is usually recommended at least 12 hours before a blood test.
Fat	A concentrated form of energy, fat is one of the three sources of macro-nutrients in food and essential for life. Fat insulates the body - insuring temperature maintenance - supplies fatty acids and carries the fat-soluble vitamins A, D, E and K. When completely broken down in the body, a gram of fat yields about 9 calories. Total fat refers to the sum of saturated, monounsaturated and polyunsaturated fats in food.
Fat-producing hormone	See Insulin.
Fatigue	The state of being tired or exhausted, fatigue represents a normal and important response to physical exertion, emotional stress or lack of sleep. It can also be a nonspecific symptom of a psychological or physiologic disorder. Pathological (illness-related) fatigue is not relieved by adequate rest, adequate sleep or removal of stressful factors.
Fatty acids	An acid originating from fats such as oleic, stearic and palmitic acid.
FDA	An acronym for the Food and Drug Administration.
Fermentation	The breakdown of complex molecules into simple molecules by enzymes.
Ferritin	An iron compound formed in the intestine and stored in the liver, spleen and bone marrow for eventual incorporation into blood molecules. Serum (or blood) ferritin levels are used as an indicator of the body's iron stores.
Fiber	See Dietary fiber.
Fibrinogen	A protein present in the blood. It becomes fibrin during the blood-clotting process.
Fibrocystic breast disease	A common glandular upset resulting in the formation of many cysts in the breasts of women. It is characterized by dense, irregular and bumpy "cobblestone" consistency in the breast tissue, discomfort and tenderness or a sense of feeling full or dull. Discomfort generally improves after each menstrual period. The cause is not completely understood but is believed to be associated with ovarian hormones since the condition usually subsides with menopause.
Fibromyalgia	A chronic disease that affects muscles, joints and tendons. It is characterized by musculoskeletal pain, spasm, stiffness, fatigue and severe sleep disturbance. Common sites of pain or stiffness include the lower back, neck, shoulder region, arms, hands, knees, hips, thighs, legs and feet. Individuals with fibromyalgia, who are mostly women, can also experience a host of symptoms such as abnormal bowel function, pain, fatigue, anxiety and depression. Physical therapy, nonsteroidal anti- inflammatory drugs and muscle relaxants can provide temporary relief.
Fight or flight response	A defense reaction that prepares individuals for conflict or escape by triggering hormonal, cardiovascular, metabolic and other physiological changes.
Fish oil	Oil from cold-water species of fish such as salmon, mackerel, tuna and cod, it contains Omega-3 fatty acids, and helps keep blood platelets from clumping, preventing the formation of clots that can cause heart attacks.
Fitness	The ability to carry out normal activities and still have enough energy and strength to overcome unusual challenges.
Fluorine	The chemical element of atomic number 9, a poisonous pale yellow gas of the halogen series. It is the most reactive of all the elements. Fluorine compounds are added to city water supplies in the proportion of about one part per million as Sodium fluoride (NaF), stannous(II) fluoride (SnF2), sodium monofluorophosphate (Na2PO3F) and Hydrofluoric acid (HF) - which are all highly poisonous to the body.
Folacin	See Folic acid.
Folate	See Folic acid.
Folic acid	A B vitamin also known as folate or folacin, necessary for growth and maintenance of health. A deficiency of folic acid may result in anemia. Studies suggest that neural tube defects, which occur in the fetus early in development, are a result of low folic acid levels in the mother's body. These studies showed that an increase in the mother's dietary folic acid before conception and during the first month of pregnancy reduced the risk of neural tube defects.
Food allergy	See Allergic reaction.
Food and Drug Administration	A government agency whose mission is to promote and protect the public health from dangerous (or as yet unproved as safe) food or drug products.
Food Intolerance	An adverse reaction to foods that does not involve the immune System, and is therefore less severe than a food allergy. A common food intolerance is lactose intolerance, caused by the inability to digest the lactose (milk sugars) found in dairy products.
Free radical	A highly reactive molecule that can bind to and destroy the body's cellular compounds. Most free radicals in the body are toxic forms of oxygen molecules. Similar to the formation of rust (oxidized iron), oxygen in its toxic state can damage (oxidize) molecules in our bodies. The body tends to produce more free radicals with age, and they are believed to play a role in the onset of degenerative diseases, as well as heart disease and cancer.
Fructose	A simple sugar found in fruit, honey, corn and saps. It has the same chemical formula as glucose and therefore may be used as a source of energy like glucose or converted to glycogen and stored in the body.