Many of us worry about our drinking and want to cut down, but finding the motivation and willpower to stick to it is hard. But what if we could change our environment so drinking less became the default? Making small changes to the environment to nudge people to behave a certain way (sometimes called choice architecture) can be effective, because a lot of our behaviour happens without conscious deliberations. In our research, we found that reducing the standard serving size of alcohol could do exactly that.

Portion sizes of food and alcohol glass sizes have increased over time and these increases have been linked with increased consumption at the population level. Experimental research shows that people eat more if they are served a larger portion of food and do not fully compensate for this by eating less later on. Conversely, reducing the portion size of food decreases how much people eat and people also don’t fully compensate for that. Based on this, we set out to experimentally test the effect of serving size on alcohol consumption. We expected that reducing the serving size of alcoholic drinks would reduce alcohol consumption.

We tested this prediction in two studies. In the first study, we invited participants to a lab that was made to look like a living room, to measure alcohol consumption in an environment where participants would feel comfortable consuming alcohol. We served half of the participants standard serving sizes of lager, cider or wine containing 2.1 units (roughly a can of beer/cider or a medium wine) and the other half were served serving sizes that were reduced by 25%. Participants could order as many drinks as they wanted whilst watching a hour-long TV programme. This enabled us to examine whether people who were served the small servings would order more drinks to compensate for the serving size reduction. Our results showed that participants who were served the reduced serving sizes of alcohol drank 20.7-22.3% less than participants who received the standard servings during the study.

It looked like reducing the serving size decreased alcohol consumption in the lab, but would this hold “in the wild”? We took our experiment to a local pub and ran four pub quiz nights during which we controlled the serving size of the drinks that attendees could buy. On two of the nights, the pub only sold standard servings of alcohol (pints, 175ml wine glasses) and on the other nights the pub only sold smaller servings (2/3 pints and 125ml wine glasses). There was no limit on the number of alcoholic drinks an individual could buy and prices were adjusted to ensure that value for money was the same on all nights. A team of experimenters posed as participants and unobtrusively recorded how much every attendee drank during the night. We found the same pattern of results as in the laboratory study: On nights that we served smaller servings, people drank 32.4-39.6% less than when we served standard servings. The next day, we asked attendees how much alcohol they drank after the quiz and found no differences in how much alcohol people drank later in the night after being serving standard or reduced servings.

“Of course people drink less if you give them less,” I hear you say. But we didn’t look at alcohol consumption from a single drink – we looked over the course of the entire drinking occasion. People were free to drink as many drinks as they wanted and had the opportunity to drink the same total amount in both conditions. In the pub quiz study, participants would have had to drink three smaller drinks to consume the same amount as two standard drinks. But people did not order more drinks to compensate for the reduced serving sizes, and as a result they drank less overall.

And there could be substantial health benefits too. We used our results in combination with the Sheffield Alcohol Policy Model to estimate that reducing the standard serving size of beer, wine and cider in bars and restaurants by a quarter would lead to 1,400 fewer deaths and 73,000 fewer hospital admissions every year.

There are many possible reasons why people might not compensate for reduced servings. It could be that people have a set expectation of the number of drinks they will have, rather than a total volume they aim for in a drinking session. Or maybe they could not be bothered to make more trips to the bar. It is also possible that consuming smaller drinks reduces the amount that seems normal to drink.

It is important to find out why people do not seem to compensate, but this does not undermine the importance of the basic effect: if you want people to drink a bit less over a single drinking occasion without restricting the amount that they are allowed to consume, then reduce the serving size. The standard serving size of beer in UK is larger than in many other countries; perhaps it is time to offer UK drinkers more options when it comes to buying smaller servings.

Dr Inge Kersbergen is a esearch associate in psychology at the University of Liverpool. Her research investigates how small changes to our immediate environment could be used to encourage healthier behaviour. She can be found on Twitter: @Inge_Kersbergen