It’s time for Day 9 of our 10 Days of Christmas Spirit countdown! And today, we have an examination of what happens to your brain when you pull out all the stops for Christmas feasts. Many people throw modesty out the window when it comes to Christmas lunch. But what do festive meal brain processes actually experience after a blow-out holiday feast?
Food plays an important role in supporting brain functions such as memory and concentration, while a balanced diet can also benefit mental health. However, questions remain about the immediate effects of overeating during festive occasions, such as a traditional Christmas dinner.
So what happens to the brain when we eat far more than usual?
What happens when we overeat?
When we eat, a range of signals around the body work together to let the brain know we are full. These include hormones released from the gut, as well as metabolites — molecules that break down food to produce energy.
These hormones also trigger the release of insulin from the pancreas to regulate blood sugar levels. This entire process is known as the “satiety cascade”.
“These signals come from different parts of our gut and work over slightly different time frames,” says Tony Goldstone, clinical associate professor at Imperial College London and consultant endocrinologist.
This cascade of hormones sent from the gut and pancreas to the brain may also play a role in the sleepy feeling many people experience after a large meal, known as postprandial somnolence. However, the precise mechanisms behind this sensation are still not fully understood.
Aaron Hengist, a postdoctoral visiting fellow at the National Institutes of Health in Washington, US, says more research is needed to understand why people feel sleepy after eating.
“The gut hormone response is a cocktail; we don’t know which specific hormones can cause sleepiness on which centres of the brain,” he explains.
It has long been believed that this so-called “food coma” occurs because blood is diverted away from the brain and towards the stomach after a large meal. However, research has shown that blood flow to the brain does not actually decrease after eating.
Is overeating harmful?
According to Hengist, eating too much on an occasional basis has surprisingly little impact on the body’s metabolism.
In 2020, he published a study examining what happens when people eat beyond being comfortably full, compared with eating until they are almost bursting. Fourteen healthy men volunteered to take part, eating large amounts of pizza in one sitting.
In one session, participants ate until they felt comfortably full. In another, they were asked to eat as much as they possibly could, consuming around double the amount of food.
Researchers measured their hormone levels, appetite, mood and metabolic responses for four hours after the meals. They found that blood sugar levels were no higher than after a normal meal, and fat levels in the blood did not increase either.
“We were surprised that, despite double the energy intake, the body regulated blood sugar remarkably well,” Hengist says. “We found that the body was working hard to do this by secreting more insulin and various gut hormones that help release insulin and signal that we’re full.”
The study suggests that a one-off indulgent meal is not as damaging as people might expect. However, Hengist cautions that the findings cannot be applied to everyone, as the study involved only young, healthy men.
When overeating lasts longer
While one large festive meal may not be harmful, research indicates that extended periods of overeating can begin to disrupt metabolism and put strain on the body, with potential consequences for the brain.
A 2021 study known as “The tailgate study” examined the effects of prolonged feasting, inspired by the American tradition of eating and drinking heavily before sports events.
In the study, 18 overweight but otherwise healthy men were given alcoholic drinks and high-fat, high-sugar foods, including burgers, chips and cake, over the course of an afternoon. On average, they consumed 5,087 calories over five hours.
Blood tests and liver scans revealed that most participants experienced an increase in liver fat following the feast.
Research has shown that non-alcoholic fatty liver disease — often linked to long-term high-fat, high-sugar diets — can reduce oxygen supply to the brain and increase inflammation in brain tissue, raising the risk of neurological conditions over time.
“The ‘tailgate’ study shows the men had metabolic dysregulation,” Hengist explains. “When passively consuming food and alcohol over multiple hours, it’s too much strain for their bodies to deal with.”
Why one big meal may not affect us
Evolution may help explain why the human body can tolerate occasional overeating.
When people are hungry, multiple biological mechanisms work together to drive food-seeking behaviour. Hunger can also affect mood, making people more irritable and more likely to crave energy-dense foods.
“It’s unclear exactly what drives ‘hanger’,” Goldstone says. “But ongoing research shows that hunger is quite an aversive state, and maybe people are eating to get rid of this state.”
Animal studies suggest that appetite-related circuits in the brain quieten when food is seen or smelled — even before it is eaten.
“The hunger made them seek food, and once they found it, that behaviour doesn’t need to continue,” Goldstone explains, adding that much of this process occurs subconsciously.
Humans have evolved to cope with periods of food scarcity, as starvation posed an immediate threat to survival. Excess food intake, on the other hand, is a more recent phenomenon with longer-term consequences rather than immediate danger.
Does the type of food matter?
Several studies in rats and mice suggest that long-term high-calorie diets can negatively affect memory and learning. Human research is more limited, but growing evidence indicates that diets high in sugar and fat can affect how the brain responds to insulin.
Stephanie Kullmann, group leader and head of the metabolic neuroimaging division at the University of Tübingen in Germany, points to a study examining brain changes after short-term overeating.
In the study, 18 healthy men consumed a high-calorie diet for five days, eating ultra-processed snacks high in fat and sugar in addition to their normal meals. On average, they consumed an extra 1,200 calories per day. A control group of 11 participants maintained their usual diet.
Brain scans showed that the high-calorie diet altered insulin responses in areas of the brain involved in appetite regulation and memory. Importantly, these changes occurred before any weight gain.
“A key finding was that the brain changes before the body,” Kullmann says. “The participants still weighed the same, but their brains looked much more similar to those of people who had been overweight or obese for years.”
One week after returning to their normal diets, participants still showed reduced responsiveness in brain regions linked to memory and cognition.
So is it OK to indulge at Christmas?
While prolonged periods of overeating- especially foods high in sugar and saturated fats- are known to be harmful to brain health, evidence suggests that a single festive feast is unlikely to cause lasting damage.
“Our study shows that one-off indulgence is not as damaging as you might expect, so enjoy your Christmas dinner,” Hengist says.
However, he warns that repeated excess over several days may place strain on the body and have longer-lasting effects on the brain- meaning moderation over the festive period still matters.
Source: BBC
Also read: Day 4: Festive menu and wine recommendations by Chef Yiannakou
For more videos and updates, check out our YouTube channel
