Encyclopedia of Diets - A Guide to Health and Nutrition

carbohydrates occur in a wide variety of foods. For

example, table sugar (sucrose) is a combination of the

glucose and fructose that occurs naturally in sugar

beet, sugar cane and fruits. Lactose is the main

sugar in milk and dairy products and maltose is a

sugar occurring in malt. Another type of carbohydrate

are the polyols, the so-called sugar alcohols. They do

occur naturally but most are made commercially by

the transformation of sugars. Complex carbohydrates

also include starch, the main energy reserve in root

vegetables and cereals. Non-starch carbohydrates are

the main components of dietary fiber. These are the

indigestible portion of plant foods, such as cellulose,

the major component of plant cell walls that consists

of several thousand glucose units. Simple sugars are

absorbed directly by the small intestine into the blood-

stream, where they are then transported to where they

are required. Complex carbohydrates are broken

down by enzymes into their constituent sugars which

are then absorbed into the bloodstream while dietary

fiber moves food through the digestive system.

Fats

Besides being a source of energy, fat stores protect

the internal organs of the body. Some essential fats

are also required for the formation of hormones.

Fats are the slowest source of energy but the most

energy-efficient form of food. Each gram of fat sup-

plies the body with about 9 calories, more than twice

KEY TERMS

Amino acid—There are 20 amino acids. The body

can synthesize 11, but the nine called essential

amino acids must be consumed in the diet.

Antibody—Aproteinproducedbythebody’simmune

system that recognizes and helps fight infections.

Biomolecule—Any organic molecule that is an

essential part of a living organism.

Calorie—A unit of food energy. In nutrition, a calorie

of food energy refers to a kilocalorie and is therefore

equal to 1000 true calories of energy.

Disaccharide—A molecule made up of two mono-

saccharides, such as sucrose, lactose, and maltose.

Enzyme—A protein that accelerates the rate of chem-

ical reactions.

Essential amino acids—The nine amino acids that

can not be made by the body: histidine, isoleucine,

leucine, methionine, phenylalanine, threonine, tryp-

tophan, and valine.

Essential fatty acids—Compounds that can not be

made by the body and must be consumed in the diet.

They include linoleic acid, linolenic acid, arachi-

donic acid, eicosapentaenoic acid, and docosahex-

aenoic acid.

Gluconeogenesis—The process of making glucose

(sugar) from its own breakdown products or from the

breakdown products of lipids or proteins. Gluconeo-

genesis occurs mainly in cells of the liver or kidney.

Glycerol—The central structural component of tri-

glycerides and phospholipids. It is made naturally by

animals and plants; the ratio of atoms in glycerol is

three carbons, eight hydrogens, and three oxygens.

Glycogen—A polysaccharide that is the main form

of carbohydrate storage and occurs primarily in the

liver and muscles. Glycogen is used as a fuel during

exercise.

Hydrocarbon—A substance consisting only of car-

bon and hydrogen atoms.

Lipoprotein—A combination of fat and protein that

transports lipids in the blood.

Monosaccharide—Any of severalcarbohydrates, such

as glucose, fructose, galactose,thatcannotbebroken

down to simpler sugars.

Polypeptide—A molecule made up of a string of

amino acids. A protein is an example of a polypeptide.

Oligosaccharide—A carbohydrate that consists of a

relatively small number of monosaccharides, such as

maltodextrins, fructo-oligo-saccharides.

Polyol—Analcoholcontainingmorethantwohydroxyl

(OH) groups, such as sugar alcohols, inositol.

Polysaccharide—Anyofaclassofcarbohydrates,such

as starch, amylose, amylopectin and cellulose, con-

sisting of several monosaccharides.

Proteases—Enzymesthatbreakpeptidebondsbetween

the amino acids of proteins.

Protein biosynthesis—Biochemical process, in

which proteins are synthesized from simple amino

acids.

Protein sequence—The arrangement of amino acids

in a protein.

Starch—Complex carbohydrate (polysaccharide)

found chiefly in seeds, fruits, tubers, and roots.

Macronutrients