Oil and fat containing food items are flushed with nitrogen because nitrogen is an inert gas that prevents oxidation. Oxygen in the air reacts with the oils and fats, causing them to oxidize and become rancid, which leads to unpleasant smells and taste changes. Flushing with nitrogen displaces oxygen inside the packaging, thus preventing oxidation, maintaining food freshness, taste, and extending shelf life. Essentially, nitrogen acts as an antioxidant by creating an oxygen-free environment that protects the food from spoilage due to rancidity.