Over half of adults in Northern Ireland eat no more than three portions of fruit and vegetables a day - well below the recommended five portions.
And 62% won't eat any fruit at least three days a week, a survey has found.
Researchers discovered seven in 10 don't know what constitutes a recommended portion of vegetables, and 75% weren't able to identify a portion of fruit - both are 80 grammes.
The details emerged in a survey by Diabetes UK for Diabetes Week, which runs until Saturday.
Jillian Patchett, national director for Diabetes UK Northern Ireland, said: "These survey results are a huge cause for concern when you recognise the fact that in the UK, 3.6 million people have been diagnosed with diabetes and 11.9 million people are at increased risk of developing Type 2 diabetes."
Over 100,000 people in Northern Ireland are living with diabetes, with an estimated 90% of those living with Type 2 diabetes.
The research also revealed that:
• Eight in 10 people don't know that a tin of baked beans could contain up to five teaspoons of sugar;
• 78% have no idea how much sugar is in salad cream, and 66% don't know how much sugar is in ketchup;
• Almost half (49%) add salt to food before even tasting it;
• Six in ten (60%) wanted to eat more vegetables but 31% thought they were too expensive.
Ms Patchett added: "Simple lifestyle changes such as eating a balanced diet, eating more fruit and vegetables and getting more exercise are an important part of managing all types of diabetes. And it can reduce the risk of serious or long term complications such as blindness, amputations and even early death.
"A healthy lifestyle can also massively reduce your risk of developing Type 2 diabetes.
"We know that obesity is one of the biggest risk factors for Type 2 diabetes, with two in three people in the UK being overweight or obese, but three in five cases of Type 2 diabetes can be prevented or delayed by maintaining a healthy weight, eating well and being active."
• Add two portions of different fruits to your porridge or muesli: raisins, dried apricots, sliced banana, blueberries or strawberries all work well.
• Having a well-stocked fruit bowl adds colour to your home and replaces biscuits or cake.
• Make vegetable crisps from beetroot, sweet potato and parsnip.
• Stew is a fantastic way to pack in extra vegetables, such as carrots, butternut squash and parsnips.
• Pack out stir fries with vegetables. Add chopped onion, garlic, peppers and mushrooms when browning your chicken or lean beef, and then broccoli, carrots, sweetcorn and peas.