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tvpjournal.com | November/December 2015 | ToDay's VeTeriNary PracTice acVN NuTriTioN NoTes Peer reviewed 69 Dietary protein is one of 3 primary metabolic fuels of the body that, together with fat and carbohydrates, provides cellular energy. amino acids extracted from dietary proteins are also used by animals to synthesize the functional proteins required for normal physiologic functions. Proteins, produced by combining amino acids, are unique energy sources because they contain nitrogen, which can be used to interconvert amino acids or synthesize other nonprotein molecules, such as nucleic acids. excess nitrogen liberated from protein processing must be eliminated to avoid toxicity. Dietary amino acids are required for life and infuence a number of conditions seen in veterinary patients, such as renal disease, liver failure, and urolithiasis. THE FOUNDATION: PROTEIN Body protein is composed of 20 different amino acids, which are linked together in long chains with peptide bonds. Proteins display complex structures, which serve a number of physiologic and biochemical processes, including: • cell signaling (eg, cytokines, hormones) • Muscle contraction (eg, cardiac contraction, locomotion) • oxygen and nutrient transport in the blood, plus oncotic support (eg, hemoglobin, albumin, ceruloplasmin) • critical reactions, such as those involved in cellular transport, enzymes, and energy production. BUILDING BLOCKS: AMINO ACIDS animals have amino acid requirements rather than intact protein requirements, which has been demonstrated in studies in which dogs and cats have been sustained on diets containing only purifed amino acids in required amounts. amino acids are absorbed in the gastrointestinal tract following disruption of peptide bonds by pepsin, trypsin, chymotrypsin, and peptidases. cells use active transport to obtain amino acids from the plasma and, subsequently, convert them to cell, tissue, or plasma proteins in target tissues. Amino Acid Structure amino acids found in tissue proteins contain an amine (nitrogen-containing) group and a carboxylic acid group linked by a carbon, known as the alpha-carbon (Figure). structures of amino acids differ in their side chains, which are attached to the alpha-carbon. Dietary Requirements commercial diets sold interstate must meet or exceed the association of american Feed control offcials (aaFco, aafco.org) recommended amounts of crude protein and each essential amino acid. 1 Essential amino acids cannot be synthesized and, therefore, must be present in the diet; The Protein Paradigm: Assessing DietAry Protein in HeAltH & DiseAse Justin Shmalberg, DVM, Diplomate ACVN & ACVSMR University of Florida The American College of Veterinary nutrition (acvn.org) and Today's Veterinary Practice are delighted to bring you the nutrition notes column, which provides the highest quality, cutting edge information on companion animal nutrition, provided by the ACVN's foremost nutrition specialists. The primary objectives of the ACVN are to: • Advance the specialty area of veterinary nutrition • Increase the competence of those practicing in this field • Establish requirements for certification in veterinary nutrition • Encourage continuing education for both specialists and general practitioners • Promote evidence- based research • Enhance dissemination of the latest veterinary nutrition knowledge. The ACVN achieves these objectives in many ways, including designating specialists in animal nutrition, providing continuing education through several media, supporting veterinary nutrition residency programs, and offering a wide array of resources related to veterinary nutrition, such as this column. Figure. Basic structure of amino acids: glycine is the smallest amino acid, with hydrogen its only side-chain. More complex amino acids have longer side-chains, including those with aromatic rings or sulfur, examples of which are shown in the fgure.