Why does binge drinking give you the munchies?

If you were to describe your typical night out binge drinking experience, 9 times out of 10 it will conclude with the grand finalé: the unashamedly wild and predatory ambushing of the chosen fast food joint. Whether it be a big mac with nugs, a greasy kebab or a killer dominoes pizza, the avid determination to devour something as salty, greasy and carb heavy as possible is overwhelming and often inevitable after a night on the lash. It just tastes so good. In a recent survey on YouGov, people reported consuming an additional 6300 extra calories on top of what they would normally consume after a heavy night out. A recent meta analysis showed that the average fresher gains 3.4 kg during freshers year1, probably the most boozy year of their lives. But why is this? 

So that end-of-night feast has become more than a routine, it’s now an ingrained ritual. You and your mates have made it a habit. Societal norms like this can have drastic impacts on our decisions and people give in to peer pressure more easily when intoxicated. It is a well-known concept that alcohol consumption causes people to loose their inhibitions. It’s why you can make that crude joke you’d have never made sober, why you may dance with your boss at a work night out or go in for a kiss with the person you’ve had the hots for for ages. But the combination of societal norms, peer pressure, loss of self-control and increase in impulsive behaviour is not all that contributes to the over-eating phenomenon. It’s recently been shown that alcohol is able to cleverly manipulate the brain into “starvation mode”. This causes the undeniable cravings, the cravings which, physiologically, do not make sense. After a night of heavy drinking it is virtually impossible to be in a calorie deficit; alcohol is nearly as calorie dense as fat per gram. 

fMRI scans showing that alcohol induces overactivity in brain regions involved in the olfactory response to food aromas

This is not just a subjective phenomenon, it has been documented in many a scientific study. For example, a study in 35 non-obese women, which injected either alcohol or salt water directly into the blood stream, showed that those given alcohol ate significantly more calories at a buffet meal afterwards, regardless of the food choices they made. To understand how alcohol has this effect, we need to look at the mechanisms controlling hunger and food intake, a process which is normally balanced by a region of the brain called the hypothalamus. Within the hypothalamus, a group of neurones, AgrP neurones, sit which, when activated signal a ravenous hunger. When they imaged the brains of these women using fMRI scanning, they showed that this area of the brain was significantly more overactive when they were exposed to delicious food odours compared to when they were exposed to odours of non-food items2

The hypothalamus plays an important role in regulating appetite

Mice also shown this alcohol-induced overeating pattern, suggesting this is an evolutionary conserved biological phenomenon. Brain slices can be taken from these mice, and these can be used to study the complex mechanisms at play. These brain slices retain the architecture of the neurones as they would be naturally in the mouse brain, and so it is possible to inject substances into the ArgP neurones specifically. Very sensitive dyes, that only are fluorescent when a neurone is activated, have been used to show that ethanol causes hyper-activity of these neurones. This group of scientists then decided to use advanced genetic engineering techniques to completely abolish the neuronal activity of these AgrP neurones in live mice models. In these mice, alcohol no longer produced its over-eating effect3

Fluorescently labelled AgrP neurones in brain slices taken from genetically modified mice

There is also evidence to suggest that alcohol has an effect on peripheral signals determining hunger cues. Adipose tissue is actually one of the largest endocrine organs in the body- secreting hormones in the bloodstream. One of these hormones is leptin, the blood concentrations of which are directly proportional to the mass of adipose tissue on the body. Leptin acts to signal to the brain that there is plenty of energy stored as fat. As leptin levels begin to fall, the body interprets this as the body loosing its fatty energy supplies. It enters into a starvation mode to try and replenish these lost stores, stimulating hunger cues and promoting appetite. Studies have shown that alcohol consumption effectively stops leptin secretion from adipose tissue, causing it to accumulate in the adipose tissue and decreasing the levels in the blood4. Another factor contributing to the ravenous hunger.  

Leptin deficient mice get morbidly obese: they have no leptin so the body acts as though it is starving even when it’s got plenty of adipose tissue stores

So is there anything you can do to try to prevent the maccies trip? Alcohol can also cause you to become hypoglycaemic (low blood sugar), especially if you haven’t eaten anything before a binge-drinking episode. This is due to a decreased ability of the liver to break down glycogen into glucose and regulate blood sugar and also because of a hyper-responsiveness to insulin. Drops in blood sugar are detected and this is reported back to the hypothalamus, also increasing appetite. So, if you eat a balanced meal before the big night out you’ll be less likely to pig out after. But, who says you shouldn’t treat yourself to the post-booze burger? It’s not like you do it every night, right? 

(1) Vadeboncoeur, Claudia, Nicholas Townsend, and Charlie Foster. “A meta-analysis of weight gain in first year university students: is freshman 15 a myth?.” BMC obesity 2.1 (2015): 22.

(2) Eiler, William JA, et al. “The aperitif effect: alcohol’s effects on the brain’s response to food aromas in women.” Obesity 23.7 (2015): 1386-1393.

(3) Cains, S. et al. Agrp neuron activity is required for alcohol-induced overeating. Nat. Commun. 8, 14014 doi: 10.1038/ncomms14014 (2017).

(4) Otaka, Michiro, et al. “Effect of alcohol consumption on leptin level in serum, adipose tissue, and gastric mucosa.” Digestive diseases and sciences 52.11 (2007): 3066-3069.

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