Removing largest wine glass lowers alcohol consumption

Now, more and more people are knocking alcohol on the head in January in a bid to give their bodies a welcome break following a period of boozy excess over Christmas. One other - and some argue better - approach is to just drink less alcohol in the first place and behavioural scientists think they may have found a way to do exactly that. Eleni Mantzari is a lecturer at City University of London…

Eleni - If you go into a pub and you ask for a glass of wine and you're asked whether you want a small one or a large one, and you might say large, it's usually a 250 millilitre portion. It's a third of a standard bottle of wine. So we wanted to see whether not offering that and capping the size that you can get to 175ml, which is what pubs call the medium size, whether that would affect how much people would drink.

Chris - How did you actually do this and do it meaningfully so that it wasn't just a lab experiment. Because we know that when we try to do lab experiments on people, we always end up wondering whether or not we've biassed people because they know they're in a study.

Eleni - This had been done in the lab before and we wanted to see what happens when you go out into the real world. So we asked 21 pubs, bars and restaurants in England to take away their largest serving size so that the largest they offered was 175ml. The pubs took part in a 12 week study. So the first four weeks they just went about their business as usual, they offered all the serving sizes of wine, we didn't make any changes and they just shared their sales reports. And then for the next four weeks we asked them to remove that large size of wine by the glass. And again, they shared their sales reports and we could see the amount of wine that they sold during those four weeks. And then the final four weeks of the study, we asked them to reintroduce the large glass of wine. And again, they shared their sales report and we could see how much wine they sold. We took into account various things because we know that the weather influences how much people drink, the time of year and other major events, so people might drink more on a bank holiday, for example. So we took these factors into consideration, into our analysis.

Chris - Do they order differently if you take that top one away?

Eleni - Yes. So what we found was that when you take the large glass away, on average each venue sold around 420 millimetres less wine per day. So that's about 7.6% less. And just to illustrate, that's one and a half large glasses of wine. So not tremendous amounts, but it was an effect that we would call significant. So it did make a difference.

Chris - When you look at the point of sale data - because you're lucky you got the till receipts, effectively, from these venues so you can tell really what the behaviour may have switched to, not an individual, but you can tell what the volumes are doing - could you see that people were compensating? If you give them less of the big ones, do they just drink more of the small ones to compensate?

Eleni - The interesting thing that we found is that when you do not offer that large glass, which is usually the 250ml, we thought that people would just switch to the immediately smaller one, which is the 175ml. But actually, what we found is, people were switching more to the 124ml, which is the smallest one you can get.

Chris - And they weren't switching to other beverages like beer that are not wine. And so you're not missing cases because someone went and had a pint of lager rather than a big glass of wine.

Eleni - Yeah, that's a really good point. So we looked at beer and cider and we didn't find that this had any effect on those drinks. What we weren't able to look at is other things such as cocktails and spirits. But we know that beer, cider and wine is what most people order and, from the drinks that most people order, we didn't really find any switching around going on.

Chris - What do you think the public health implications of this are? Is this something that policymakers should now be actively thinking about deploying? Because we know that alcohol is a top five killer, isn't it? If you look at the World Health Organization figures, alcohol causes more disease and more loss of life than many other things that we regard as major threats.

Eleni - This is just one study. For policy makers to make a decision, they would probably want to see more research on the topic. But this study does suggest that there could potentially be some regulation about the larger sizes and maybe capping it. There are many things to consider, such as the acceptability of this by the public and the hospitality industry and the alcohol industry as well.

Chris - Is it me or have glasses of wine got larger in recent years, though? I'm sure, when I was in my student days - wasn't that long ago - you didn't see people walking around with what looks like a bucket full of wine and now you can get a half a bottle of wine in some of these wine glasses that you're routinely seeing for sale.

Eleni - So there have been two things that have happened. The actual wine glasses have gone up, their size. So we did some research within our group at Cambridge and we measured wine glasses over time and we saw that they have increased, especially since the nineties, almost 400% in some cases. And there is research that shows that if you have larger wine glasses, you tend to pour more in them. But also the portion sizes that are being offered has increased. When I was at uni, I don't think you could ever get a 250 millilitre glass as the standard glass. The standard used to be the 125ml. It's shifted what's considered normal towards the bigger end.