Final answer:
White bread is the least effective option in lowering blood cholesterol levels because it generally contains lower levels of fiber compared to foods like oatmeal, apples, and broccoli which are rich in soluble fiber.
Step-by-step explanation:
To lower blood cholesterol levels by consuming foods high in fiber, it is important to select items rich in soluble fiber because this type of fiber can help decrease cholesterol levels by forming a gel-like substance in the gastrointestinal tract. Of the options given, white bread would be the least effective for lowering cholesterol as it typically contains lower levels of fiber compared to whole grain alternatives. In contrast, oatmeal, apples, and broccoli are all good sources of soluble fiber and are more effective in managing cholesterol levels.