Low ambient temperatures stimulate the pig's appetite and thus its feed intake because additional energy is required to maintain the pig's body temperature. Body temperature is regulated after heat is released from both the digestion and tissue metabolism of carbohydrates, fats, and proteins. The heat generated by the digestive and metabolic process of feeds is called "heat increment." This heat can be beneficial as well as detrimental to subsequent pig performance. Dietary fat results in a lower amount of heat released during the digestion and metabolic process and thus has a low heat increment. Dietary protein and fiber release more heat during the digestion and metabolic process, and these feed components therefore have a high heat increment. High ambient temperatures can depress the pig's feed intake. Consequently, when the pig is stressed by high environmental temperatures or from high body heat, the pig attempts to produce less heat by consuming less feed. Consequently, the incorporation of fat into the pig's diet will have less of a detrimental effect on the pig's feed intake at a high ambient temperature because less heat is being generated and less body heat will need to be dissipated. Supplemental dietary fats/oils may therefore be helpful when hotter environmental temperatures are expected. In contrast, because high fiber feeds result in a higher heat increment, diets with a higher fiber content will be more beneficial during colder temperatures where the additional heat generated from the digestive process is used to keep the body warm. However, diets high in fiber content can be detrimental in a hot environment. Pigs fed in drylots or open-front buildings require more energy to maintain their body temperature during the colder seasons than pigs fed in complete confinement where conditions are temperature-controlled.