Many of us go all out for Christmas lunch, but what does a big festive meal do to our bodies and brains?
Food plays a key role in brain function, supporting memory, concentration, and mental health. But how does overeating, such as during a Christmas feast, affect the brain immediately?
What Happens When We Overeat?
When we eat, the gut releases hormones and metabolites that signal the brain we’re full. These hormones also trigger insulin release from the pancreas to regulate blood sugar. This process is called the “satiety cascade.”
Tony Goldstone, clinical associate professor at Imperial College London, says these signals come from different parts of the gut and act over slightly different time frames.
The hormone cascade may also explain the sleepy feeling after a big meal, known as “postprandial somnolence.” But Aaron Hengist, a postdoctoral visiting fellow at the National Institutes of Health in Washington, notes the exact mechanism is unclear.
Many people believe a “food coma” happens because blood moves from the brain to the stomach, but research shows blood flow to the brain doesn’t decrease after a large meal. Hengist adds, “The gut hormone response is a cocktail; we don’t know which specific hormones cause sleepiness in which brain centres.”
Is Overeating Harmful?
Occasional overeating seems to have little effect on metabolism. Hengist conducted a 2020 study on 14 healthy men who ate pizza in two ways: until comfortably full and until they were about to burst. In the second session, they ate double the amount.
The researchers measured hormones, appetite, mood, and metabolism for four hours afterward. Blood sugar and fat levels remained similar to those after a normal meal. Hengist says, “Despite double the energy intake, the body regulated blood sugar remarkably well, secreting more insulin and gut hormones to signal fullness.”
This suggests a one-off indulgence is not as harmful as expected. However, the study involved only young, healthy men, so results may not apply to women or people who are overweight or obese.
Does Duration and Frequency Matter?
While one pizza-eating session may be fine, multiple hours or a whole day of feasting can strain metabolism and the brain.
In 2021, researchers conducted the “tailgate study,” simulating American pre-sports game parties with alcohol and high-fat, sugary foods. Eighteen overweight but healthy men consumed an average of 5,087 calories over five hours. Blood tests and liver scans revealed increased liver fat in most participants, showing prolonged overeating can have negative effects.
