Final answer:
The most appropriate dietary instruction for a client with a high LDL level is to keep saturated fat intake below 10% of total calories.
Step-by-step explanation:
The most appropriate dietary instruction for a client with a low-density lipoprotein (LDL) level of 158 mg/dL would be option a: "You should keep your saturated fat intake below 10% of your total calories." This is because reducing saturated fat intake can help lower LDL cholesterol levels and decrease the risk of heart disease. Option b is incorrect because an LDL level of 158 mg/dL is considered high and requires dietary modifications. Option c is not specific to LDL cholesterol and option d restricts protein sources unnecessarily.