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Why does feeding motivation rise when an animal’s fuel supply is low?

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Two wild horses graze on tall grass in the open prairie of Theodore Roosevelt National Park, with rolling badlands visible in the background. — Feeding behaviour Wild horses graze in the Badlands of North Dakota.

Feeding motivation rises when an animal’s fuel supply is low because the body employs complex physiological monitoring systems to maintain homeostasis.12

When fuel levels drop due to catabolism and the emptying of the digestive tract, the body generates signals that report this nutritional state to the brain. These signals, which include information about blood glucose availability and fat tissue stores, converge on brain mechanisms—specifically within the hypothalamus and limbic system—to increase feeding motivation.134

As these hunger signals override satiety signals, the animal’s responsiveness to food increases, prompting behaviors such as searching and ingestion. Additionally, hormones like ghrelin, which is produced in the stomach and hypothalamus, play a key role by stimulating appetite when caloric intake is restricted. This interplay of feedback ensures that, over time, an animal's caloric intake balances its energy output, keeping body fuel content relatively constant.132