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Failure to Thrive
A condition in which the child does not grow normally.
Familial Polyposis
An inherited disease causing many polyps in the colon. The polyps often cause cancer.
Fasting blood glucose test
The test is usually done in the morning before breakfast. The normal range for blood glucose is from 70 to 110 mg/dl. If the level is over 126 mg/dl, it usually means the person has diabetes (except for newborns and some pregnant women).
Fats
One of the three main classes of foods and a source of energy in the body. Fats help the body use some vitamins and keep the skin healthy. There are two types of fats: saturated and unsaturated. Saturated fats are from animal food products. Some examples are butter, lard, meat fat, solid shortening, palm oil, and coconut oil. These fats tend to raise the level of cholesterol in the blood. Unsaturated fats are monounsaturated fats and polyunsaturated fats. These are derived from plant oils such as olive, peanut, corn, cottonseed, sunflower, safflower, and soybean. These fats tend to lower the level of cholesterol in the blood. See also: Carbohydrate; protein.
Fatty acids
A basic unit of fats. 
Fatty Liver  
The accumulation of fat in liver cells. The most common cause is alcoholism. Other causes include obesity, diabetes, and pregnancy. 
Fecal Fat Test 
A test to measure the body's ability to break down and absorb fat. The patient eats a fat-free diet for 2 to 3 days before the test and collects stool samples for examination.
Fecal Incontinence  
Unable to hold stool in the rectum.
Fecal Occult Blood Test (FOBT)  
A test  blood in the stool that is not visible to the naked eye. 
Fiber  
A substance found in foods that come from plants. The two types of fiber in food are soluble and insoluble. Soluble fiber, found in beans, fruits, and oat products, dissolves in water and is thought to help lower blood fats and blood glucose (sugar). Insoluble fiber, found in whole-grain products and vegetables, passes directly through the digestive system, helping to rid the body of waste products.
Fibrin
The insoluble protein formed from fibrinogen by the proteolytic action of thrombin during the normal clotting of blood.
Fibroblast
pertaining to fibroblasts, or connective tissue cells
Fibromyalgia
A chronic disorder characterized by widespread musculoskeletal pain, fatigue, and multiple tender points.
Fibrous capsule
A tough wrapping of tendons and ligaments that surrounds the joint.
Fistula
An abnormal canal between two organs or between an organ and the outside of the body. 
Flatulence
Excessive gas in the stomach or intestine. May cause bloating.
Flare
A period of time in which disease symptoms reappear or become worse.
Flatus  
Gas passed through the rectum.
Flolic acid
It is in viatmin B complex involved in the formation of red blood cells
Foodborne Illness  
An acute gastrointestinal infection caused by food that contains harmful bacteria. Symptoms include diarrhea, abdominal pain, fever, and chills. 
Fructose
A type of sugar found in many fruits and vegetables and in honey. Fructose is used to sweeten some diet foods.
Fulminant Hepatic Failure (FHF)
Liver failure that occurs suddenly in a previously healthy person. 
Functional Disorders
Disorders such as irritable bowel syndrome. These conditions result from poor nerve and muscle function. Emotional stress can trigger symptoms. Synonym: motility disorders.
Fungus
A mold or yeast that may cause infection.