Fiber – also known as roughage, is usually a carbohydrate which cannot be digested. It passes through the human digestive system without being digested or absorbed. Soluble fiber will absorb water in the intestine. Fiber has effects on intestinal operations, and by extension, on other tissues. It seems to have an effect on vascular health. The mechanisms by which these effects happen are largely speculative at present. One effect of dietary fiber, apparently especially soluble fiber, has is to increase stool size and softness. Dietary fibers, when eaten together with carbohydrates, delay the uptake of the carbohydrates.
Fasting blood glucose test - A method for finding out how much glucose is in the blood, at a time when recent food intake does not affect glucose levels. This test can be used when diagnosing diabetes a reading of 126 mg/dl (7 mmol/l) is diagnostic except in newborns or pregnant women or in some unusual other conditions. The test is often done in the morning before the person has first eaten via a blood test. The normal, range for fasting blood glucose for a non diabetic is between 70 to 110 mg/dl (5 - 7 mmol/l). It can now also be done by anyone with a blood glucose meter, proper supplies, and an understanding of how to test using them.
Fats - Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Food substances are the chief energy storage mechanism in organisms such as plants and animals. Fat molecules are composed of fatty acid chains attached to a glycerol backbone. Fats may be either solid or liquid at room temperature, depending on their structure and composition. Possibilities include saturated (the usual case in animal source fats), mono or poly unsaturated (from many plant oils, have one (mono) or more (poly) double carbon bonds in the fatty acid chain), and in where the double bond is (at the omega carbon in the 3 position, or the 6 position or ...). Some fats are required in the human dietary needs, they are the 'essential oils'. All other fats humans need can be made, at the cost of some energy, from those fats, or from other chemicals.
Fatty acids - chains of carbon atoms with attached side groups. They are found in living tissues, typically in the form of triglycerides (three fatty acid chains attached to a glycerol backbone).
Fluorescein angiography - is a technique for examining the circulation of the retina using the dye tracing method. It involves injection of sodium fluorescein into the systemic circulation, and then an angiogram is obtained by photographing the fluorescence emitted after illumination of the retina with blue light at a wavelength of 490 nanometers.
Food exchange - See: Exchange lists.
Foot care – This is especially important for all diabetics. Good care includes daily examination of the feet, toes, and toenails and choosing shoes and socks or stockings that fit well and so do not cause pressure points, binding, or pinching. Non elasticised socks are the best to choose from, especially if Edema (water retention) is present. People with diabetes have to take special care of their feet because of nerve damage and altered blood flow mean they will have less feeling in their feet than normal, and poorer healing than usual. They may not notice cuts and other problems as soon as they should. They will also heal less well than others. Diabetics should never walk barefoot, as they may not always feel cuts or scratches to the feet.
Fractional urine - Urine that a person collects for a certain period of time during 24 hours; usually from breakfast to lunch, from lunch to dinner, from dinner to bedtime, and from bedtime to rising. Also called "block urine."
Fructose – is a simple sugar mainly found in fruits which does not participate in the glucose metabolism control system. In the human diet, fructose is largely found in most fruits but in the past few decades, it has been used as a sweetener in foods in the form of high fructose corn syrup.
fructosamine test - measures the number of blood glucose molecules linked to protein molecules in the blood system. The test provides information on the average blood glucose level for the past 3 weeks.
Fruit sugars - and the sugar substitutes that end in ‘ose’ are a fructose based sweetener, these may cause a laxative effect to the user.
Fundus of the eye - The central portion of the retina on back or deepest part of the eye. Damage to the fundus, even if the rest of the eye is in good condition, will have severe problems. For instance reading may become impossible.
Funduscopy - A test to look at the back area of the eye to see if there is any damage to the vessels that bring blood to the retina. The doctor uses a device called an ophthalmoscope to check the eye. There is also a special type of camera which takes photos of the eye (with dilated pupils) to record retinal conditions for future comparison.