In this condition, assume a person just started into phase I of the Atkins Diet and he/she has just consumed a meal of all protein and fat with no carbohydrates. As a result, this person is in an anabolic state, but blood glucose levels are low, meaning the pancreas will secrete glucagon.

Liver glycogen stores will be broken down to secrete glucose for other tissues. Glycolysis will not be occurring to any great extent, in order to spare glucose for other tissues. Using amino acids from digestion and lactate from muscle, gluconeogenesis will synthesize glucose that will also be secreted. From the breakdown of amino acids, there will be an increase in the synthesis and secretion of urea from the liver to safely rid the body of ammonia from the amino acids. Amino acids will also be used for protein synthesis. Some triglycerides from chylomicron remnants taken up will be broken down to fatty acids. These will then be broken down to acetyl-CoA and used to synthesize ketone bodies that are secreted for tissues, such as the brain, that cannot directly use fatty acids as a fuel. Other triglycerides will be packaged into VLDL and secreted from the liver.

The muscle is going to break down glycogen to glucose, and receive glucose from the liver that enters glycolysis, forming pyruvate. Glucose will be used for anaerobic (lactate) and aerobic (pyruvate) respiration. After glycogen is used up, most glucose will be used for anaerobic respiration to spare glucose. In aerobic respiration, pyruvate will enter the transition reaction to form acetyl-CoA. The acetyl-CoA will then enter the citric acid cycle, and NADH and FADH2 produced will enter the electron transport chain to generate ATP. Once there is not enough glucose for the muscle to use, fatty acids will be cleaved from and taken up from chylomicrons, chylomicron remnants, VLDL, IDL, and LDL and broken down to acetyl-CoA. The acetyl-CoA will then enter the citric acid cycle, and NADH and FADH2 produced will enter the electron transport chain to generate ATP. Amino acids taken up will be used for protein synthesis, and lactate will be secreted for the liver to use for gluconeogenesis (Cori cycle).

In the adipose, fatty acids that are cleaved from chylomicrons, chylomicron remnants, VLDL, IDL, and LDL are also going to be taken up. These fatty acids will be used to synthesize triglycerides for storage. With glucagon levels high in this condition, hormone-sensitive lipase would be active. However, since this is an anabolic state, the net effect would be uptake of fatty acids after cleavage by lipoprotein lipase. The adipose won’t be secreting anything under this condition.

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