Which of the following is NOT a dietary source of alpha-linoleic acid?

Alpha-linoleic acid (ALA) is an essential omega-3 fatty acid primarily found in plant-based sources. It is crucial for human health and must be obtained through the diet. The correct choice here is beef, as it is an animal product and does not significantly contain ALA.

Walnuts, soy, and spinach are all excellent sources of alpha-linoleic acid. Walnuts are well-known for their high ALA content, making them a popular recommendation for plant-based omega-3 intake. Soy products, including tofu and soy milk, also provide ALA and are widely recognized for their health benefits, particularly in vegetarian and vegan diets. Spinach, while not as concentrated a source as the other options, still contains some levels of ALA and contributes to the dietary intake of omega-3s.

In contrast, beef and other red meats typically do not provide ALA but may contain other types of fatty acids, like saturated fats or omega-6 fatty acids. Therefore, beef stands out as the option that does not contribute to dietary alpha-linoleic acid intake.