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Why did evidence challenge the idea that stomach contractions alone cause hunger?

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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.

The "local theory of hunger" once suggested that hunger signals originated in the gastrointestinal tract, specifically that hunger pangs were caused by stomach contractions. However, this theory was challenged and ultimately deemed inadequate by several key findings:

Surgical removal: Research demonstrated that a significant portion of the stomach can be removed without causing a loss of hunger motivation.
Nerve severance: Studies showed that severing the vagus nerve—which stops stomach contractions—does not eliminate the experience of hunger.

Because these contractions are not necessary for the sensation of hunger, researchers shifted their focus toward brain mechanisms, particularly the role of the hypothalamus in regulating eating behavior.1