Chapter 24 Nutrition, Metabolism, and Energy Balance

Nutrient

substance in food needed for growth, maintenance, and repair

Macronutrients

three categories of nutrients making up most of the diet: carbohydrates, lipids, and proteins

Micronutrients

vitamins and minerals, required in small but essential amounts

Metabolic fuel

primary use for most nutrients, though some are for building molecules and cells

Water

essential substance accounting for about 60% of food volume

Essential nutrients

molecules the body cannot synthesize in adequate amounts and must be provided by the diet

Nonessential nutrients

hundreds of molecules the body can synthesize, often by liver interconversions

Kilocalories (kcal)

unit measuring nutrient energy; the heat needed to raise the temperature of 1 kg of water by 1°C

Carbohydrate and Protein Energy Value

4 kcal per gram

Lipid Energy Value

9 kcal per gram

USDA MyPlate

guidelines for food portions: fruits, vegetables, grains, protein, and dairy

Basic Dietary Principles

eat only what you need; eat plenty of fruits, vegetables, and whole grains; avoid junk food

Carbohydrate Dietary Sources

mostly plants; lactose in milk; small amounts of glycogen in meat

Sugars

monosaccharides and disaccharides found in fruits, sugarcane, honey, and milk

Starch

polysaccharide found in grains and vegetables

Insoluble fiber

cellulose in vegetables that provides roughage to increase stool bulk and facilitate defecation

Soluble fiber

pectin in apples and citrus that helps reduce blood cholesterol levels

Glucose

the primary carbohydrate molecule used by cells to produce ATP

Fructose and Galactose

sugars converted to glucose by the liver before entering circulation

Neurons and RBCs

cells that rely almost entirely on glucose and die quickly without it

Glycogen or Fat

forms in which excess glucose is stored

Pentose sugars

carbohydrates used for building nucleic acids

Glycocalyx

cellular structure built using short-chain sugars

Carbohydrate Dietary Requirements

45-65% of total daily calories, ideally from complex carbohydrates

Carbohydrate Excess Problems

obesity, diabetes mellitus, dental caries, elevated triglycerides

Carbohydrate Deficit Problems

tissue wasting, metabolic acidosis from accelerated fat use

Lipid Dietary Sources

primarily triglycerides

saturated fats in meat/dairy

unsaturated in seeds/nuts

trans fats in hydrogenated oils

Cholesterol Sources

egg yolks, meats, organ meats, shellfish, and milk products

Liver Cholesterol Production

the liver produces about 85% of blood cholesterol regardless of intake

Essential Fatty Acids

linoleic acid (omega-6) and linolenic acid (omega-3), which the liver cannot make

Adipose Tissue

provides protective cushioning, insulation, and energy storage

Myelin Sheaths

neuronal structures largely composed of phospholipids

Cholesterol Functions

stabilizes cell membranes; precursor for bile salts and steroid hormones

Prostaglandins

regulatory molecules made from linoleic acid involved in BP regulation and inflammation

Lipid Dietary Requirements

20-35% of total caloric intake; saturated fats limited to 10% or less

Lipid Excess Problems

obesity; increased risk of cardiovascular disease

Lipid Deficit Problems

weight loss; heat loss control issues; poor growth; skin lesions; depression

Complete Proteins

animal products and soybeans that meet all essential amino acid requirements

Incomplete Proteins

legumes, nuts, and grains LOW in one or more essential amino acids

All-or-None Rule

all amino acids needed for a specific protein must be present simultaneously or the protein cannot be built

Caloric Adequacy

if carbohydrate or fat intake is insufficient, body proteins will be burned for energy instead

Anabolic Hormones

GH and sex hormones that promote protein synthesis

Glucocorticoids

hormones that promote protein breakdown and conversion of amino acids to glucose

Positive Nitrogen Balance

synthesis exceeds breakdown; occurs during growth, pregnancy, and tissue repair

Negative Nitrogen Balance

breakdown exceeds synthesis; occurs during stress, infection, or starvation

Protein Dietary Requirement

0.8 g per kilogram of body weight daily

Protein Deficit Problems

profound weight loss; edema due to low plasma proteins; miscarriage or premature birth

Vitamins

organic compounds acting as coenzymes; needed in minute amounts for macronutrient use

Vitamin D

vitamin synthesized in the skin

Vitamins B and K

vitamins synthesized by intestinal bacteria

Beta-carotene

a provitamin found in carrots that the body converts to Vitamin A

Water-soluble Vitamins

B complex and C; absorbed with water; not stored in the body

Fat-soluble Vitamins

A, D, E, and K; absorbed with lipids; stored in body fat (except Vitamin K)

Antioxidants

Vitamins A, C, and E

neutralize harmful free radicals

Seven Major Minerals

Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, and Magnesium

Iron

component of hemoglobin and electron carriers; deficiency causes anemia

Iodine

essential component of thyroid hormones; deficiency causes goiter

Calcium and Phosphorus

minerals used to harden bone

Sodium and Chloride

major electrolytes in blood

Metabolism

the sum of all biochemical reactions in the body

Anabolism

reactions that build larger molecules from smaller ones; requires energy

Catabolism

reactions that break down complex structures into simpler ones; releases energy

Cellular Respiration

catabolic reactions (glycolysis, Krebs, ETC) that capture chemical energy as ATP

Phosphorylation

transfer of a high-energy phosphate group to prime a molecule for work

Oxidation

the gain of oxygen or the loss of hydrogen and electrons

Reduction

the gain of hydrogen and electrons; results in a gain of energy

Dehydrogenases

enzymes that catalyze the REMOVAL of hydrogen atoms

Oxidases

enzymes that catalyze the transfer of oxygen

NAD+ and FAD

B-vitamin coenzymes that act as hydrogen and electron acceptors

Substrate-level Phosphorylation

direct transfer of phosphate from a substrate to ADP; occurs in glycolysis and Krebs

Oxidative Phosphorylation

Mitochondrial process using a proton gradient to synthesize the most ATP

Glycolysis

anaerobic process in cytosol; 1 glucose becomes 2 pyruvic acids; yields 2 ATP and 2 NADH

Lactic Acid

formed from pyruvic acid when oxygen is not available

Citric Acid Cycle (Krebs)

mitochondrial aerobic process;

breaks down pyruvic acid to CO2;

yields ATP and reduced coenzymes

Electron Transport Chain (ETC)

use of high-energy electrons from NADH/FADH2 to pump protons and create a gradient

ATP Synthase

rotary motor protein that uses proton flow to attach phosphate to ADP

Glycogenesis

synthesis of glycogen from glucose when ATP levels are high

Glycogenolysis

breakdown of glycogen to glucose when blood sugar is low

Gluconeogenesis

formation of new glucose from non-carbohydrate sources like glycerol and amino acids

Beta Oxidation

breakdown of fatty acid chains into two-carbon acetic acid fragments

Lipogenesis

triglyceride synthesis when cellular ATP and glucose levels are high

Lipolysis

breakdown of stored fats into glycerol and fatty acids for fuel

Ketogenesis

liver conversion of excess acetyl CoA into ketone bodies during rapid fat breakdown

Transamination

transfer of an amine group from an amino acid to a keto acid

Oxidative Deamination

removal of an amine group as ammonia in the liver; ammonia is then converted to urea

Absorptive State

the four hours after eating where anabolism exceeds catabolism and nutrients are stored

Insulin

the primary hormone of the absorptive state; lowers blood glucose and promotes storage

Postabsorptive State

the fasting state where energy stores are broken down to maintain blood glucose

Glucagon

the primary hormone of the postabsorptive state; promotes glycogenolysis and gluconeogenesis

Diabetes Mellitus

disorder of inadequate insulin or abnormal receptors, leading to metabolic acidosis and protein wasting

HDL (High-density lipoproteins)

"good" cholesterol; transports excess cholesterol from tissues back to the liver

LDL (Low-density lipoproteins)

"bad" cholesterol; transports cholesterol to peripheral tissues

VLDL (Very low-density lipoproteins)

transport triglycerides from the liver to adipose tissue

Liver Functions

processes nearly every nutrient; detoxifies; stores vitamins A, D, B12, and Iron

Basal Metabolic Rate (BMR)

energy used for essential activities at rest and fasting

Total Metabolic Rate (TMR)

total calories needed for BMR plus ALL voluntary physical activities

Thyroxine

major hormone controlling BMR

increases oxygen consumption and heat production

Leptin

hormone from fat cells that suppresses appetite as fat stores increase

Ghrelin

appetite stimulant from the stomach that peaks before meals

Hypothalamus

the body's main integration center for temperature regulation