An ice fisherman has fallen through the ice. In response to the cold water, sensors in the man's skin send a "cold" signal to the in the man's brain, which in turn sends signals to muscle cells to begin to contract. As a result of this process, the fisherman begins to shiver

Hypothalamus

Explanation:

homeostasis in terms of body temperature involves maintaining a constant temperature as much as balancing the internal and external temperature of man. For humans, normal temperature is about 98.6°F (37°C). When your hypothalamus senses that you’re too hot, it sends signals to your sweat glands to make you sweat and cool you off. When the hypothalamus senses that you’re too cold, it sends signals to your muscles that make your shiver and create warmth. This is called maintaining homeostasis. The hypothalamus also maintains homeostasis in lots of other ways, such as by controlling your blood pressure.

Vigorous shivering increased the body's heat energy.

i would have a lunch. it's one big package of food, making it one food. : p