Lipids are insoluble in water but can dissolve in certain organic sol- vents (e.g., ether and benzene). Lipids yield more energy per gram than carbohydrates- on average, 9 calories per gram. Note that the term fats refers to lipids that are solid at room temperature, whereas oils are those that are liquid at room temperature. (Fiber provides little energy because it cannot be broken down by digestive processes.) Lipids Like carbohydrates, lipids are compounds composed mostly of the elements carbon, hydrogen, and oxygen. It and most other carbohydrates provide an average of 4 calories per gram (kcal/g). Glucose, which comes from simple carbohydrates and starch, is a major source of energy in most cells. As you'll see in Chapter 5, starch and fiber differ in the way the glucose molecules are linked together. The yellow hexagons represent the glucose molecules that make up starch and fiber. Simple Carbohydrates Complex Carbohydrates Starch Sugar Readily usable form of carbohydrates Storage form of carbohydrate in foods Fiber structure Indigestible carbohydrate that forms struc of plant cell walls The simple sugars are represented by the yellow hexagons (glucose). Fiber, another type of complex carbohydrate, forms the structure of plants. Examples of complex carbohydrates include the starch in grains and the glyco- gen stored in our muscles. Some sugars, such as glucose, can chemically bond together to form large carbohydrates, called polysaccharides or com- plex carbohydrates. Small carbohydrate structures are called sugars or simple carbohydrates table sugar (sucrose) and blood sugar (glucose) are examples. The main types of carbohydrates are simple and complex.
Fruits, vegeta- bles, grains, beans, and sugars are the primary dietary sources of carbohydrate.
Energy-Yielding Nutrients Carbohydrate Lipids (Fats and Protein (Amino Acids) Oils) Glucose (or a Linoleic acid Histidine Lysine Threonine carbohydrate that (omega-6) a- Methionine Isoleucine Leucine Tryptophan Valine yields glucose) Phenylalanine Linolenic acid (omega-3) Carbohydrates Carbohydrates are composed mainly of the elements carbon, hydrogen, and oxygen. Nutrients are substances essential for health that the body cannot make or that it makes in quantities too small to support health. The Chemical and Physical Structures of Lipids, Carbohydrates, and Proteins You probably are already familiar with the terms carbohydrates, lipids (fats and oils), and proteins.
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