Restaurants and supermarkets are being urged to reduce their portion sizes to tackle obesity in the UK following research that suggests people eat and drink more when offered bigger portions.

The study conducted by the University of Cambridge suggests eliminating larger portion sizes after finding people have a tendency to consume more food and drink non-alcoholic drinks when using larger tableware.

The review claims to contain the most conclusive evidence to date that suggests people’s tendency to overeat – which is linked to heart disease, diabetes, and many cancers – might be attributed to ‘overserving’ of bigger portions.

By reducing these portions, the study suggests that UK adults could reduce their calorie intake by up to 16% and up to 29% in the US.

The extent to which overconsumption might be attributed to big portions has never been known; now the Behaviour and Health Research Unit has combined results from 61 studies, capturing data from 6,711 participants, to investigate the influence of portion, package and tableware size on food consumption.

The results, published in the Cochrane Database of Systematic Reviews, show people consistently consume more when offered larger portions, packages or tableware.

It suggests that if exposure to these could be reduced in all aspects of people’s diet it could reduce average daily energy consumed from food by 12% to 16% among adults in the UK.

There was no differentiation between men and women or people’s body mass index (BMI), susceptibility to hunger, or tendency to consciously control their eating behaviour.

Dr Gareth Hollands who co-led the review, said: “It may seem obvious that the larger the portion size, the more people eat, but until this systematic review the evidence for this effect has been fragmented, so the overall picture has, until now, been unclear. There has also been a tendency to portray personal characteristics like being overweight or a lack of self-control as the main reason people overeat.

“In fact, the situation is far more complex. Our findings highlight the important role of environmental influences on food consumption. Helping people to avoid ‘overserving’ themselves or others with larger portions of food or drink by reducing their size, availability and appeal in shops, restaurants and in the home, is likely to be a good way of helping lots of people to reduce their risk of overeating.”

Large reductions would be needed to achieve the changes in food consumption suggested by the results.

The researchers highlight a range of potential actions that could be taken to reduce the size, availability or appeal of larger-sized portions, packages and tableware, including: upper-limits on serving sizes of energy-dense foods and drinks (for example, fatty foods, desserts and sugary drinks), or on the sizes of crockery, cutlery and glasses provided for use in their consumption; placing larger portion sizes further away from purchasers to make them less accessible; and demarcating single portion sizes in packaging through wrapping or a visual cue.

Hollands said: “With the notable exception of directly controlling the sizes of the foods people consume, reliable evidence as to the effectiveness of specific actions to reduce the size, availability or appeal of larger-sized food portions is currently lacking and urgently needed.”

The researchers suggest that some of the highlighted actions to limit portion size are likely to require regulation or legislation, helped by active demand from the public for changes to the food environment. “At the moment, it is all too easy – and often better value for money – for us to eat or drink too much,” said Ian Shemilt, who co-led the review. “The evidence is compelling now that actions that reduce the size, availability and appeal of large servings can make a difference to the amounts people eat and drink, and we hope that our findings will provide fresh impetus for discussions on how this can be achieved in a range of public sector and commercial settings.”