Final answer:
Buttermilk would be the permitted food on a fiber-restricted diet as it does not contain fiber, unlike options with high fiber content such as whole-wheat bread, chunky peanut butter, and winter squash.
Step-by-step explanation:
The food that would be permitted on a fiber-restricted diet among the options provided is d. buttermilk. This is because whole-grain products like whole-wheat bread, chunky foods with seeds like chunky peanut butter, and vegetables high in fiber such as winter squash are usually restricted on a fiber-restricted diet due to their high fiber content.
Buttermilk, on the other hand, is a dairy product and does not contain fiber, making it a suitable choice for someone who needs to limit their fiber intake.