Just 4% of young people in Northern Ireland are eating enough fruit and vegetables, a report said.
Adults and older children are falling well behind the rest of the UK when it comes to eating the recommended amount, according to a report from the Food Standards Agency in Northern Ireland and the Department of Health.
The study found that 96% of children aged 11-18 did not eat five a day, and neither did 82% of adults aged between 19 and 64, nor 77% of those aged 65 and over.
Ruth Balmer, senior scientific adviser at the FSA in Northern Ireland said: "These figures are alarming and everyone needs to be aware that poor eating habits increase our risk of developing diet-related diseases and health problems.
"It is startling that so few of our young people and teenagers - just 4% - are eating the recommended amount of fruit and vegetables and it shows us just how much work we need to do with young people and teenagers."
The report said people were eating too much saturated fat and not enough oily fish while men and boys were having too much red and processed meat.
Marian Faughnan, chief specialist in nutrition with the safefood health authority, said: "It's clear that changes are needed.
"Consumers tell us they want practical advice to help them make changes to their diet, for example, cutting down on sugary and fatty treat foods or replacing sugary drinks with water.
"These small changes are easier to sustain in the long run and can have a big impact on our health, especially among our children and teenagers."
Other findings of the National Diet and Nutrition Survey revealed:
:: The amount of fibre consumed was significantly less than the rest of the UK
:: A third of adults aged 19 to 64 years in Northern Ireland had low blood levels of vitamin D, which can lead to conditions like rickets, a higher proportion than in the UK as a whole
:: The lowest income group had lower fruit and vegetable consumption than those with the most money. They also had lower intakes of starch and some vitamins and minerals
Analysis of food consumption and nutrient intake was based on 470 adults and 512 children between 2008 and 2012.
Health minister Jim Wells said 62% of adults were overweight or obese.
Consumption of sugary, fizzy drinks and squashes, and chips and fried foods and meat products, with the exception of confectionery, tended to be higher in the lowest income/most deprived groups, and higher in Northern Ireland compared with the rest of the UK.
Salt intake was higher than the maximum recommended level for young people aged 11 to 18 and adults from 19 to 64 years.