It’s not just what you are eating that causes obesity, but how much, say researchers

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Researchers at the University of Cambridge say they have the “most conclusive evidence to date” that portion control, or rather a lack of it, is contributing to the obesity crisis.

While a diet high in fat and sugar is widely understood to contribute to obesity and type 2 diabetes, the concept of quantity control, including which proportions of each food group should be included in a balanced meal, can lead to confusion say researchers. If regularly eaten to excess, even relatively ‘healthy’ foods can lead to weight gain.

The researchers at the Behaviour and Health Research Unit at Cambridge analysed 61 studies involving 6,711 people and say that their findings indicate that simple portion control could help people cut their calorie intake by around 16%, which over time could result in weight loss. They also found that people have what is perhaps an acquired tendency to eat whatever is put in front of them, often regardless of how full they are feeling.

In addition, the researchers, who published their analysis in the Cochrane Database of Systematic Reviews, say that portion sizes of many everyday foods, such as pies, ready meal lasagne and pasta dishes have been steadily increasing in the UK since 1993, as published in the government report Food Portion Sizes. They believe that the government should do more to encourage manufacturers to provide smaller quantities when packaging high-calorie foods, discouraging overconsumption, which may also help people on a budget to reduce their food bill.

Dr Gareth Hollands from the Behaviour and Health Research Unit, who co-led the review, says: “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.”

Impact on health

In addition to short term issues including bloating, tiredness and digestion problems, overeating can lead to weight gain and a host of health problems related to obesity, including increased cancer risk, cardiovascular disease and diabetes.

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The British Heart Foundation (BHF) has been calling for consistency in portion sizes since 2013, when it published its report Portion Distortion. The BHF report found what was described as “huge variations” in portion sizes for similar meals according to manufacturer or brand and that, while portion sizes for some foods, including individual ice creams and oven chips, had decreased, portion sizes for some convenience foods had increased dramatically compared to 1993, including ready meals such as shepherd’s pie and chicken curry, which were found to have increased in size by as much as 98%.

Professor Brian Ratcliffe, Emeritus Professor of Nutrition at Robert Gordon University, says of the review: “It provides evidence to support what might seem to be a self-evident truth that serving larger portions leads to greater levels of consumption, and the effect seems to be more pronounced in adults than children.

“Presumably related to a lack of effective self-restraint, people seem to be reluctant to leave or waste food and so consume what they are served or find larger portions more attractive. The authors conclude that the effects are modest, nevertheless, changing portion sizes or offering a range of them could help people to control their food intakes and reduce the risks of becoming overweight or obese.”

The way forward

Professor Ratcliffe says that restaurants and other food outlets could do more to offer a range of portion sizes, with reduced pricing, which would help people make healthier choices. He adds that this approach could “be a way forward to help people to avoid overconsumption”.

“At the moment, it is all too easy – and often better value for money – for us to eat or drink too much,” says Ian Shemilt, who co-led the review alongside Dr Holland. “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.”

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Tips on reducing your portion size

If you believe you may be eating more than you should at mealtimes there are a number of things you can do to cut down and get back on track. If you’re the sort of person who dislikes food waste and feel the need to clear your plate regardless of how full you are feeling, try switching your serving plates to smaller ones.

Check on the back of your food packaging to see what a ‘portion’ actually is. You might be surprised to find that one serving of your favourite dessert is actually one sixth of that cheesecake instead of the quarter that you normally have. If you don’t follow the portion guidelines, you will need to recalculate the recommended daily intake references when it comes to fat, salt and sugars and many people get into the habit of overeating because they regularly overestimate portion size.


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About the author

Georgie Fenn, writes most of our news articles and social media posts.