Which of the following are effects of diet on the body's immune system as…

Concept — a literal-comprehension question is settled by what the passage itself asserts, not by what is generally true of the subject. The reader locates the claim the text actually makes and matches it, idea for idea, with a value; a value that adds information the text never supplies is set aside however plausible it sounds in general nutrition science.

Application — the passage builds one chain about food and the body's defences: most of the body's immune system is concentrated in the gut, the gut holds trillions of healthy bacteria called the microbiome, and therefore "what we eat has a direct impact on how the immune system functions". The surrounding lines repeat the same claim: "what we eat affects the health of the entire body, including the immune system", Heather Moday's remark that the science linking food and immunity "is crucial", and Kristin Kirkpatrick's warning that even a month of ignoring nutrition "can impact the microbiome". The effect the text names is therefore a direct impact on how the immune system functions.

Cross-check — measure the remaining values against the text:

• Increased cholesterol levels: the passage's single quantitative reference to food is "avoiding excess calories", and it never moves from calories to any blood-lipid measure.

• Improved skin health: the body systems the passage names are the gut, the microbiome and the respiratory tract (colds, flu and other respiratory illnesses); the skin never enters its discussion.

• Loss of appetite: the passage describes eating more, not less — "culinary indulgence" and "throwing caution to the wind till New Year's Day" — so a reduced drive to eat is not the effect under discussion.

Result — the effect of diet on the immune system that the text discusses is a direct impact on how the immune system functions.