A study has estimated that the annual cost arising from people who are overweight or obese in the Republic of Ireland is more than €1bn.
The figure for Northern Ireland is put at more than €500m.
The research, which was conducted by University College Cork, identified the costs in healthcare and in reduced or lost productivity and absenteeism.
According to the study, almost €400m of the total spend relates directly to healthcare costs.
It also found that 65% of the total (€730m) was as a result of lost productivity and absenteeism.
Cardiac disease, Type-2 Diabetes and colorectal cancer were found to be among the main drivers of healthcare costs of 18 weight-related diseases studied.
Researchers said the figures are conservative and do not reflect the human and societal costs.
The safefood-funded research found that overweight and obesity combined accounted for an estimated 2.7% of total healthcare expenditure in the State.
Safefood's Director of Human Health and Nutrition Dr Cliodhna Foley-Nolan said education about healthy eating needs to begin very early in a child's life.
She said: "We should be going into families. By the time children even reach primary school, many of them have an established pattern of poor energy balance, in other words, they're eating too much generally and too much of the wrong food, and also they're not as active as they should.
"So while schools are an important vehicle, home really, and parental recognition, that is the big issue.
"We can now say that this costs roughly 3% of the health budget; that the major contributors are heart disease and cancers, in terms of healthcare costs and in terms of absenteeism.
"Perhaps surprisingly, the biggest single cause of the problem is low back pain and heart disease, once again, in terms of premature mortality, so this gives us an economic basis on which to work."