Inability to understand the calories in routine meals puts multitude at risk of grave illnesses like cancer, heart disease and diabetes.
A survey commissioned for World Cancer Research Fund found that two-thirds of UK adults underestimated the level of calories in foods such as houmous and so-called "light" mayonnaise.
Just 32 per cent correctly said houmous was high in calories and only 29 per cent that low-fat mayo was also high in calories, the Daily Express reported.
"Despite decades of increasing awareness about calories and healthy eating, it seems a lot of people are still confused about the calorie content of everyday foods," Maya Monteiro, senior education manager at WCRF, said.
"This troubling lack of understanding is perhaps not helped by labels such as 'light' and 'reduced fat' when applied to foods which still have a high calorie content."
"The study also highlights the importance of having a system of food labelling that is both easy to understand and widely used."
Both houmous and "light" mayonnaise are in fact high-calorie foods with houmous containing an average of 332 calories per 100g and "light" or "reduced-fat" mayonnaise containing an average of 259 calories.
A fifth (20 per cent) of the 2,128 adults questioned for the research believed that bananas were high in calories even though the fruit contains just 95 calories per 100g on average.
"Many people make New Year's resolutions to lose weight but it is important that they understand how to determine whether a food is high in calories. Reduced fat doesn't necessarily mean low fat. It is important for -people to be able to make informed choices about food," Monteiro added.