Of the 20 amino acids in the body, 10 are ESSENTIAL AMINO ACIDS . They must be present in the diet because they cannot by synthesized in the body in adequate amounts. They are isoleucine, leucine, lysine, methionine, phenyalanine, threonine, tryptophan, valine, arginine, and histidine. A complete protein includes all essential amino acids. Examples include alfalfa , flaxseed, soybean meal, sunflower meal, wheat bran, rice bran & canola.
Metabolic Adaptations
Regulation of metabolic reactions depends both on the chemical environment within the body cells such as levels of ATP and O2, and on signals from the nervous system and endocrine system. Absorptive State : ingested nutrients are entering the bloodstream, and glucose is readily available for ATP production. A typical meal requires about 4 hours for absorption. Post absorptive State : absorption of nutrients from the GI tract is complete, and energy needs must be met by fuels already in the body. The nervous system and RBCs depend on glucose for ATP production during the post absorptive state. Therefore, maintaining a steady blood glucose level is critical during this period. Hormones are dominant (major regulators) of metabolism in each state. Insulin is dominant during the absorptive state, while several other hormones such as glucagon have key roles during the post absorptive state.
Metabolism during the Absorption State
Very soon after a meal, nutrients start to enter the blood. The forms are mainly glucose, amino acids, triglycerides (chylomicrons). Two metabolic hallmarks of the absorptive state are: Oxidation of glucose for ATP production occurring in most cells Storage of excess fuel molecules for future “between-meal” use occurring mainly in hepatocytes, adipocytes, and skeletal muscle fibres.
Absorptive State Reactions:
1. ~50% of absorbed glucose from a typical meal is oxidized by body cells to produce ATP via Glycolysis, Krebs Cycle, and Electron Transport Chain.
2. ~10% glucose enters hepatocytes to be converted to Glycogen.
3. Adipocytes take up the remaining 40% of glucose and convert it to triglycerides for storage.
4. Some fatty acids and triglycerides are synthesized in the liver and remain there, but hepatocytes package most into lipoproteins which carry lipids to adipose tissue for storage.
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