Women eat more when they dine with men because they do not want to give the impression that they constantly count calories.
Research from Safefood on portion sizes also found that men see eating as a test of manhood, and this stops them from going for smaller portions.
Women increase their portion sizes if they are eating with a man because they do not want to appear to be mean with food.
The report also found that consumers only regard portion sizes as being relevant to those dieting, more important to women and not an issue for men or younger adults.
The research, led by the University of Ulster, found that occasions such as eating with friends or eating out presented a challenge when trying to control portion sizes.
The report found that food products with health or nutrition claims like 'low fat' or 'reduced fat' may also be contributing to weight gain, as many people assume these products are lower in calories than they really are and consume larger portions.
Commenting on the findings, Dr Cliodhna Foley-Nolan from Safefood said: "Traditionally, we've been brought up to finish everything on our plate and we tend to equate bigger portions with generosity and value. But with two in three adults overweight or obese, the issue of portion size is relevant to all of us and we need to cut down on the portions we're eating of most foods".
The research also revealed tips identified by consumers which they have found helpful in cutting down on their portion sizes: these included eating until satisfied (rather than full), filling up with water, vegetables or fruit and eating more slowly.
Meanwhile, another study found that pregnant women who are overweight can cause health problems for their children in later life.
A major European obesity study found youngsters were more likely to suffer conditions including mood disorders, cardiovascular disease, and type 2 diabetes.
The most recent figures show obesity affects one in six adults in the EU - up from one in eight a decade ago.
Lunchtime took to the streets today to find out if people agree that this happens.
They also spoke with Safefood’s Dr Foley-Nolan about the issue.
