Chapter 18

what is nutrition?

study of nutrients in the body

what are nutrients?

Chemicals from the environment that organisms need for survival

Used to supply energy to fuel metabolic processes, and for building blocks for producing the molecules the body needs

what are the two major nutrient classes?

macronutrients

micronutrients

what is macronutrients?

Required in large quantities, such as carbohydrates, lipids, proteins; provide energy

what is micronutrients?

required in small amounts, such as vitamins and minerals; help extract energy from macronutrients

what are essential nutrients?

Nutrients that the body cannot synthesize or cannot synthesize in sufficient quantity

Must be obtained from the diet

what are calories?

Units of heat used to express amount of energy in foods

what are carbohydrates?

Organic compounds, such as sugars and starches

Energy held in their chemical bonds is used to power cellular processes

what are the three carbohydrate sources?

polysaccharides, disaccharides, monosaccharides

what are polysaccharides?

Complex carbohydrates, such as starch from plant foods and glycogen from meats

what are disaccharides?

(double sugars): milk sugar, cane sugar, beet sugar, molasses

what are monosaccharides?

(single sugars) from honey and fruits

Digestion breaks complex __ into monosaccharides that are small enough to be absorbed

carbohydrates

Cellulose is a __ carbohydrate abundant in our food; not digested, but provides fiber

complex

Different __ are absorbed from digestive tract: fructose, galactose, and glucose

monosaccharides

Since __ is the most common cellular fuel oxidized in glycolysis, the other monosaccharides are converted into glucose by enzymes in the liver

glucose

Glucose is broken down into CO₂, H₂O, and __ when needed

energy

Excess glucose is converted into __ by glycogenesis, and stored in liver and muscle cells

glycogen

After storing a certain amount of glycogen, excess glucose is converted into __ by lipogenesis, and stored in the adipose tissue

fats

Many cells can __ down fatty acids for energy, but some require glucose

break

what is gluconeogenesis?

Conversion of noncarbohydrates (amino acids, glycerol) to glucose, for cells that require glucose as energy source

what is the primary source of fuel for cellular processes?

carbohydrates

does the need for carbohydrates vary with individual energy requirements?

yes

Minimal requirements for carbohydrates in the human diet is unknown, but an intake of at least 125 to 175 __/day is likely necessary

grams

Average diet in the United States includes 200 to 300 grams/__.

day

what are lipids?

Organic compounds that include fats, oils, phospholipids, and cholesterol

Supply energy for cellular processes

Serve as building blocks for structures such as cell membranes

what are triglycerides?

Composed of glycerol and 3 fatty acids

Most common dietary lipids 

Also called “fats”

what kind of foods are triglycerides found in?

plant-based and animal-based foods

what are saturated fats?

Mainly in foods of animal origin, such as meat, eggs, milk, and lard 

Also in palm and coconut oils

No double bonds between carbon atoms in fatty acids

Associated with increased risk of cardiovascular disease

what are unsaturated fats?

Found in seeds, nuts, and plant oils

Contain one or more double bonds between carbon atoms

Monounsaturated fats are the healthiest

what is cholesterol?

Abundant in liver and egg yolk

Some in whole milk, butter, cheese, and meats

Not found in foods of plant origin

Lipids in foods include phospholipids, __, and most commonly, fats/triglycerides

cholesterol

what are the functions of lipids?

Mainly supply energy

Contain more than twice as much chemical energy per gram as carbohydrates or proteins

Triglycerides are broken down to glycerol and fatty acids, in order to release energy

Glycerol and fatty acids can be used to synthesize storage fats in adipose tissue

Excess glucose or __ acids can also be converted into fat molecules

amino

can the liver convert fatty acids from one form to another?

yes

Liver cannot synthesize certain fatty acids, called essential __ acids; these must be obtained from the diet.

fatty

Lipids can combine with proteins to form __.

lipoproteins

what are lipoproteins?

Classified on the basis of density; as proportion of lipids decreases, density increases

Used in lipid transport to specific target cells

what are VLDLs?

(very low density lipoproteins): high triglyceride content

what are LDLs?

(low density lipoproteins): high cholesterol content

what are HDLs?

(high density lipoproteins): high protein content

how does the liver control cholesterol?

Produced by the liver, and released into the blood

Can be used to make bile salts

Excreted in bile

how is adipose tissue used?

stores and releases triglycerides as needed