Eating large food portions can significantly increase our weight even during short periods – researchers at the University of Ulster have discovered in the first ever study of its kind. 

Many people are feeling the pinch in their clothes at this time of year after overindulging at Christmas but instead of cutting back on certain foods, eating smaller portions could be the answer.  

A team of nutritionist researchers, led by Professor Barbara Livingstone and Dr Mary Kelly from Ulster’s Biomedical Sciences Research Institute, has carried out the first study in controlled conditions, of how eating different portion sizes impacts on energy intake and body weight. 

And the results were dramatic - in just four days men eating three large meals a day piled on an extra kilo, while women weighed an extra half a kilo on the scales.   

The study was carried out at a residential facility in the University’s Coleraine campus where 43 adults – 21 men and 22 women – a mix of normal weight and overweight volunteers, lived for four consecutive days. 

The subjects were randomly split into two groups where they ate either standard or large portions over two four-day periods which were spread three weeks apart. 

Professor Livingstone outlined the reasons behind carrying out this investigation. 

“In the past few decades several key environmental and cultural factors have converged to increase the probability of over-eating in the face of reduced energy needs,” she said. 

“One environmental factor which has become the focus of attention is that of food portion size, which has been increasing steadily over the past two decades in parallel with the rise in overweight and obesity. 

“Studies have demonstrated that portions of food sold in supermarkets, fast food establishments and restaurants have steadily increased since the mid 1980s – a trend that has been most apparent and best documented in the USA. 

“Therefore it is thought that increasing portion sizes of food may be undermining normal appetite control and inciting over-eating.  

“One possible reason for over-eating is that consumers tend to eat what they are served even if it is an inappropriate amount for their energy needs and consequently may not compensate for this over-consumption at subsequent eating occasions.  

“However, despite pervasive commercial trends towards large food portions, there was surprisingly little hard evidence that these are casually linked to excess energy intake or indeed obesity. 

“Therefore while the proposition that large portion sizes promote over-consumption is intuitively logical, to date studies have been specific to the US context, and while supportive, have been conducted under semi-controlled conditions. Therefore, the extent to which these findings would be relevant to the UK population was unknown.” 

Dr Kelly explained the importance of the University of Ulster study. 

“The data from this study provides evidence to support the general consensus that larger food portions may be a contributing factor to the obesity epidemic,” she said. 

“Our subjects stayed overnight in the Human Intervention Studies Unit at the University and all food eaten over a four day period was weighed, leftovers were also weighed, so we knew the exact amount of food being consumed. 

“One of the issues today is that people don’t know anymore what a standard portion size is - we are all eating larger portions. It may be the case that consumers have become so accustomed to larger food portions that are now the ‘norm’ in many of our eating environments that standard portions are no longer perceived as being adequate. 

“One of the most surprising results from this study was that the subjects didn’t feel any fuller after eating the larger portions.”  

Dr Kelly and Professor Livingstone recently published a report on the study in the British Journal of Nutrition. In that paper they recommended that health promotion agencies focus on education in the area of portion control.  

“A possible approach could be to attempt to alert individuals to the importance of recognising and responding to the physiological cues of appetite and satiety, as well as an increased awareness of the environmental factors, such as food portion size that can influence increased food consumption,” said Dr Kelly.  

“However, the onus for the ‘downsizing’ of large portion sizes to help bring food portions  back in line with energy requirements cannot rest with consumers alone and will need to be facilitated by appropriate measures on the part of the food  industry.”