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
|↑ Glucose Uptake||Muscle, Adipose||↑ GLUT4|
|↑ Glucose Uptake||Liver||↑ Glucokinase|
|↑ Glycogen Synthesis||Liver, Muscle||↑ Glycogen Synthase|
|↓ Glycogen Breakdown||Liver, Muscle||↓ Glycogen Phosphorylase|
↑ 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
|↑ 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.