"Alcohol switches the brain into starvation mode, increasing hunger and appetite, scientists have discovered," BBC News reports.
Research in mice found alcohol increased activity in a set of brain cells used to regulate appetite.
Scientists have long been puzzled about why people often eat more when they've been drinking alcohol, despite the high number of calories in alcoholic drinks. Alcohol is second only to fat in its calorie density.
The body's regulatory system should register calories arriving in the body, so that the person would not feel hungry. But with alcohol the opposite happens – people feel hungry and eat more.
Researchers found that mice ate more when given alcohol. They saw spikes in electrical activity in Agouti-related peptide cells (AGRP cells) from the mice brains when they were exposed to alcohol. AGRP cells are specialised brain cells the body uses to regulate appetite. While hunger may hit you in your stomach, the entire process of "hunger, eat, reward" is controlled by your brain.
When the mice's AGRP cells were chemically blocked, they no longer ate more when given alcohol.
Research in animals doesn't always translate to humans, so we don't know for sure if this means the same thing happens in human brains. However, it is plausible.
It's also a reminder that if you're trying to watch your weight – alcohol will set you back in more ways than one; it is chock full of calories in its own right, and it may well make you eat more on top.
Where did the story come from?
The study was carried out by researchers from the Francis Crick Institute and University College London and was funded by the Francis Crick Institute, which itself is funded by Cancer Research UK, the UK Medical Research Council, and the Wellcome Trust.
The BBC summarised the results reasonably accurately, saying that while the research was in mice, the researchers "believe the same is probably true in humans".
But the Daily Mail barely mentioned that the research was carried out in mice, and that animal research does not necessarily translate into humans.
What kind of research was this?
This was experimental animal research, carried out in a laboratory on mice bred for experimental purposes. While animal research can give us clues to what may be happening in human bodies, there are plenty of differences between mice and humans. This means we can't rely on the results being true for humans.
What did the research involve?
Scientists carried out a series of experiments on laboratory mice, to see what effect ethanol (pure alcohol) had on their eating behaviour and brain cells. They examined tissue from mice brains, to see how certain brain cells responded to ethanol, and looked to see what happened when they blocked receptors for those cells.
The first experiments included giving 10 mice the mouse equivalent of 18 human units of alcohol a day (about a standard bottle and a half of wine) for three days. The alcohol was given by injection into the body, to ensure all mice got the same amount and that their appetites weren't affected by the taste. Researchers weighed how much food the mice ate each day. This was compared to food eaten on the days before and after the alcohol dose.
They then took brain samples from genetically modified mice and looked to see what effect ethanol had on AGRP nerve cells from the hypothalamus of the brain. They used calcium activity markers (a technique that helps brain activity to show up on brain scans) and measured electrical activity. They also blocked AGRP cells using chemicals, and looked to see what effect that had on brain cells and on mice eating habits, with and without alcohol.
What were the basic results?
The mice ate between 10% and 25% more food on the days when they'd been given ethanol. This dropped back down to previous levels after the alcohol was stopped.
Experiments on brain tissue showed that AGRP cells were activated and had spikes in electrical activity when exposed to alcohol.
When the researchers blocked the mice's AGRP cells with an inert drug, alcohol no longer had an effect on how much the mice ate. Blocking the cells, without alcohol, made less difference to how much they ate, suggesting that the interplay of AGRP and alcohol was what affected the mice's eating most strongly.
How did the researchers interpret the results?
The researchers suggest that the alcohol-associated activity of the AGRP brain cells "is the critical step in alcohol-induced overeating".
They say their findings "provide an explanation for how a commonly consumed nutrient [alcohol] may generate a positive feedback on energy intake," and that this may help doctors better understand over-eating leading to ill-health in humans.
Alcohol is no friend of people trying to lose weight, or stick to a healthy weight. Not only is it high in calories (the second most energy-dense nutrient after fat), but it tends to be linked to a desire to eat more.
Scientists have suggested various theories to explain this. One theory is that alcohol erodes willpower, meaning people are likely to eat more than they intended after a drink. That could also explain why people often pick less healthy options, such as crisps or kebabs, if they've been drinking.
This new research suggests an alternative explanation – that the specific effect of alcohol on brain cells could trigger "an attack of the munchies".
But while the results seem reasonably convincing for mice, we still don't know if they hold true for humans. Also, rather than drinking it, the mice were given injections of alcohol, which might have a different effect.
Even so, the research is a reminder that alcohol and overeating can go hand in hand. If you're planning on shifting a few pounds in 2017, cutting back on alcohol, or avoiding it entirely, could be a positive first step.
In the UK, the government recommends that men and women drink no more than 14 units of alcohol a week. That is:
- nine small glasses of average strength wine
- seven pints of average strength beer or lager
- 14 single measures of spirits
The advice is to spread those units over three or more days, and to have several alcohol-free days each week.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 11 January 2017
BBC News, 10 January 2017
Links to the science
Nature Communications. Published online January 10 2017