People eat fewer snacks when portion sizes are clearly marked on packaging.
The ESRI’s Behavioural Research Unit carried out two studies into people's eating habits and found if the portion sizes are clearly marked then people will eat less.
However, the effects differed on gender, with men eating fewer crisps served at a venue and women having fewer biscuits at home.
With people snacking more during lockdown and with Christmas approaching dietician Orla Walsh has these tips for people who are concerned about their eating habits:
"I encourage people to eat really slowly, use all five senses and really enjoy your chocolate or your crisps."
Ms Wash says traffic light systems or grams aren't a good indicator.
"When you give specific amounts to people they know instantly how much per person it is."
"We don't always have our weighing scales or our glasses to read the small font with us," she said.
The Department of Health cites portion size control as one method to help reduce levels of obesity.