If a subject is fed a diet that supplies both protein and all essential amino ac

Question

If a subject is fed a diet that supplies both protein and all essential amino acids at the requirement level (not in excess), but the diet contains only half of the individuals energy requirement.
a. The individual would be in negative energy balance
b. Protein breakdown would be greater than protein synthesis
c. Amino acids would be used as a fuel (for energy)
d. Urea excretion would increase compared with what would be excreted in the individual had consumed the same diet supplemented with carbohydrate and fat.
e. All of the above
Explain:

Explanation / Answer

Amino acids would be used as a fuel (for energy) Dietary carbohydrate from which humans gain energy enter the body in complex forms, such as disaccharides and the polymers starch (amylose and amylopectin) and glycogen. The polymer cellulose is also consumed but not digested. The first step in the metabolism of digestible carbohydrate is the conversion of the higher polymers to simpler, soluble forms that can be transported across the intestinal wall and delivered to the tissues. The breakdown of polymeric sugars begins in the mouth. Saliva has a slightly acidic pH of 6.8 and contains lingual amylase that begins the digestion of carbohydrates. The action of lingual amylase is limited to the area of the mouth and the esophagus; it is virtually inactivated by the much stronger acid pH of the stomach. Once the food has arrived in the stomach, acid hydrolysis contributes to its degradation; specific gastric proteases and lipases aid this process for proteins and fats, respectively. The mixture of gastric secretions, saliva, and food, known collectively as chyme, moves to the small intestine. The main polymeric-carbohydrate digesting enzyme of the small intestine is a-amylase. This enzyme is secreted by the pancreas and has the same activity as salivary amylase, producing disaccharides and trisaccharides. The latter are converted to monosaccharides by intestinal saccharidases, including maltases that hydrolyze di- and trisaccharides, and the more specific disaccharidases, sucrase, lactase, and trehalase. The net result is the almost complete conversion of digestible carbohydrate to its constituent monosaccharides. The resultant glucose and other simple carbohydrates are transported across the intestinal wall to the hepatic portal vein and then to liver parenchymal cells and other tissues. There they are converted to fatty acids, amino acids, and glycogen, or else oxidized by the various catabolic pathways of cells. Oxidation of glucose is known as glycolysis.Glucose is oxidized to either lactate or pyruvate. Under aerobic conditions, the dominant product in most tissues is pyruvate and the pathway is known as aerobic glycolysis. When oxygen is depleted, as for instance during prolonged vigorous exercise, the dominant glycolytic product in many tissues is lactate and the process is known as anaerobic glycolysis

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