Nutrition

Nutrients

• Nutrition is the taking in and the use of food.

• Nutrients are the chemicals used by the body and consist of carbohydrates, lipids, proteins, vitamins, minerals, and water.

• Essential nutrients cannot be produced by the body or cannot be produced in adequate amounts.

Kilocalories

• A kilocalorie is the energy required to raise the temperature of 1000 g of water from 14°C to 15°C. A kilocalorie is the unit of measurement used to express the energy content of food.

Carbohydrates

• Carbohydrates include monosaccharides, disaccharides, and polysaccharides.

• Most carbohydrates we ingest are from plants.

• Carbohydrates are used as an energy source and for making DNA, RNA, and ATP.

• The recommended amount of carbohydrate is 125 to 175 g daily.

Lipids

• Lipids include triacylglycerol, phospholipids, steroids, and fat-soluble vitamins. Triacylglycerol is a major source of energy. Prostaglandins are involved in inflammation, tissue repair, and smooth muscle contraction. Cholesterol and phospholipids are part of the cell membrane. Some steroid hormones regulate the reproductive system.

• It is recommended that fats account for no more than 30% of the total kilocaloric intake.

Proteins

• Proteins are chains of amino acids.

• Animal proteins tend to be complete proteins, whereas plant proteins tend to be incomplete.

• Proteins are involved in structural strength, muscle contraction, regulation, buffering, clotting, transport, ion channels, receptors, and the immune system.

• The recommended daily consumption of protein is 0.8 g/kg of body weight per day.

Vitamins

• Most vitamins are not produced by the body and must be obtained in the diet. Some vitamins can be formed from provitamins.

• Vitamins are important in energy production, nucleic acid synthesis, growth, and blood clotting.

• Vitamins are classified as either fat-soluble or water-soluble.

Minerals

• Minerals are necessary for normal metabolism and add mechanical strength to bones.

Metabolism

• Metabolism consists of anabolism and catabolism. Anabolism is the synthesis of molecules and requires energy. Catabolism is the breaking down of molecules and gives off energy.

• The energy in carbohydrates, lipids, and proteins is used to produce ATP.

Regulation of Metabolism

• Biochemical pathways are a series of chemical reactions, some of which release energy that can be used to synthesize ATP.

• Each step in a biochemical pathways requires enzymes.

• Enzyme synthesis is determined by DNA. Enzyme activity is modified by receptor-mediated and end product processes.

Carbohydrate Metabolism

• Glycolysis is the breakdown of glucose to two pyruvic acid molecules. Two ATP molecules are also produced.

• Anaerobic respiration is the breakdown of glucose in the absence of oxygen to two lactic acid molecules and two ATP molecules.

• Lactic acid can be converted to glucose using aerobically produced ATP; the necessary oxygen is the oxygen debt.

• Aerobic respiration is the breakdown of glucose in the presence of oxygen to produce carbon dioxide, water, and 38 molecules of ATP.
  • The first phase of aerobic metabolism is glycolysis.

  • The second phase of aerobic metabolism is the conversion of pyruvic acid to acetyl-CoA.

  • The third phase of aerobic metabolism is the citric acid cycle.

  • The fourth phase is the electron-transport chain, which uses carrier molecules such as NADH to synthesis ATP.

Lipid Metabolism

• Lipids are broken down in adipose tissue, and fatty acids are released into the blood.

• Fatty acids are taken up by cells and broken down into acetyl-CoA, which can enter the citric acid cycle. Acetyl-CoA can also be converted into ketones by the liver. Ketones released from the liver into the blood are used as energy sources by other cells.

Protein Metabolism

• Amino acids are used to synthesize proteins.

• Amino acids can be used for energy, and ammonia is produced as a by-product.
  • Ammonia is converted to urea and excreted by the kidneys.

Metabolic States

• In the absorptive state, nutrients are used as energy or stored.

• In the postabsorptive state, stored nutrients are used for energy.

Metabolic Rate

• Metabolic rate is the total energy expenditure per unit of time.

• Metabolic energy is used for basal metabolism, muscular activity, and the assimilation of food.

Body Temperature Regulation

• Body temperature is a balance between heat gain and heat loss.

• Heat is produced through metabolism.

• Heat is exchanged through radiation, conduction, convection, and evaporation.

• The greater the temperature difference, the greater the rate of heat exchange.

• Body temperature is regulated at a "set point" by neural circuits in the hypothalamus.