Final answer:
The food item that is not a major contributor of healthful fatty acids among the options is Butter. While Salmon, Walnuts, and Avocado are rich in unsaturated fats that are beneficial for health, Butter is primarily composed of saturated fats, which are less beneficial and should be consumed in moderation.
Step-by-step explanation:
The student's question relates to identifying a food source which is not a major contributor to healthful fatty acids. Among the options provided, Salmon, Walnuts, and Avocado are known for their high content of healthful unsaturated fatty acids. Salmon, along with other oily fish like trout and tuna, is rich in omega-3 fatty acids which are essential for brain function and may help prevent heart disease and cancer. Walnuts and other nuts such as pecans are a good source of predominately polyunsaturated fats, specifically omega-3 fatty acids.
Avocado is known for its content of predominately monounsaturated fats, which are part of a healthy diet. In contrast, Butter is primarily composed of saturated fatty acids, which can increase the risk of heart disease if consumed in excess. Saturated fats are primarily found in animal products and should be consumed in limited quantities. Consequently Butter would be the food item among the options that is not a major contributor of healthful fatty acids.