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7.4: Metabolic Conditions

You have learned about the pathways and the tissue metabolic capabilities, so now we’re going to apply that knowledge to three conditions: fasting, the Atkins diet, and the Ornish/Pritikin diet, as ways to illustrate how you can use this knowledge. In fasting, we’re going to be considering what is happening metabolically during a prolonged period without food. This is a catabolic condition. The Atkins diet is a carbohydrate-restricted diet, so we are going to consider what happens metabolically when someone is eating a diet that essentially only contains protein and lipids over an extended period of time. This is an anabolic condition. Finally the Ornish/Pritikin diet is a very low fat diet, so we’re going to consider what happens metabolically when someone is eating a diet that is essentially only carbohydrates and protein over an extended period of time. This is an anabolic condition. For each of these conditions, we’re going to consider what is happening in the liver, muscle, adipose, and brain.

Now that you should have an understanding of the glycemic response and macronutrient metabolism, you should be able to understand the broader effects of insulin and glucagon that are summarized in the following tables. Knowing what hormone is elevated in the different conditions helps you to understand the metabolism that occurs in different conditions.

Table 7.41 Insulin’s effects on targets in tissues1,2

Effect

Tissue

Target

↑ Glucose Uptake

Muscle, Adipose

↑ GLUT4

↑ Glucose Uptake

Liver

↑ Glucokinase

↑ Glycogen Synthesis

Liver,  Muscle

↑ Glycogen Synthase

↓ Glycogen Breakdown

Liver, Muscle

↓ Glycogen Phosphorylase

↑ Glycolysis,

↑ Transition Reaction

Liver, Muscle

↑ Phosphofructokinase-1

↑ Pyruvate Dehydrogenase Complex

↑ Fatty Acid Synthesis

Liver

↑ Fatty Acid Synthase

↑ Triglyceride Synthesis

Adipose

↑ Lipoprotein Lipase


Table 7.42 Glucagon’s effects on targets in tissues2

Effect

Tissue

Target

↑ Glycogen Breakdown

Liver

↑ Glycogen Phosphorylase

↓ Glycogen Synthesis

Liver

↓ Glycogen Synthase

↑ Gluconeogenesis

Liver

Multiple Enzymes

↓ Glycolysis

Liver

↓ Phosphofructokinase-1

↑ Ketone Body Synthesis

Liver

↑ Acetyl-CoA Carboxylase

↑ Triglyceride Breakdown

Adipose

↑ Hormone-Sensitive Lipase

References & Links

1. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.

2. http://jpkc.gmu.cn/swhx/book/shyl/23.pdf