Final answer:
Ingestion of 1000 kcal of fat would likely have the greatest impact on the rate of postprandial fat oxidation due to the high calorie content, although protein has a higher S.D.A. The body's metabolism and fat oxidation also depend on overall diet composition and nutritional state.
Step-by-step explanation:
The impact of macronutrient ingestion on the rate of postprandial fat oxidation varies depending on the type of food consumed and its specific dynamic action (S.D.A.). Ingestion of 500 kcal of carbohydrate, while significant, may not have the greatest impact due to the relatively low S.D.A. of 6%.
Comparatively, the ingestion of protein stimulates metabolism, typically causing a maximum increase of 30% in metabolic rate, making it a strong candidate. However, ingestion of 1000 kcal of fat would likely have the greatest absolute impact on the rate of postprandial fat oxidation due to the sheer number of calories provided, even though fat has a lower S.D.A. of 4%.
It's important to recognize that, although protein has a higher S.D.A., this doesn't directly correlate to a greater impact on fat oxidation post-meal versus the large caloric intake from 1000 kcal of fat. The body's capacity to oxidize fat will also depend on the existing nutritional state and the macronutrient composition of the diet.