According to the Health Food Manufacturers' Association (HFMA), some 38m adults mistakenly believe potatoes count as one of their "five-a-day" portions of fruit and vegetables.

The shocking statistics open up further potential for the use of supplements to help plug the nutritional blackhole.

HFMA nutritionist, Dr Marilyn Glenville said: "With only 15 per cent of women and 13 per cent of men eating the recommended five-a-day fruit and vegetables, it is important that people are trying to keep themselves in good health by using supplements on a daily basis."

Indeed, according to the survey of 3,300 people, the HFMA estimated that some 32m adults already take supplements, with multivitamins proving he most popular.

HFMA Director, David Adams, added: "With more than 18m adults regularly taking vitamin and mineral supplements, we know that as a nation, we are increasingly taking charge of our health through enhanced nutrition.

"But while it is heartening to see that high numbers of people are boosting health and wellbeing with supplements, it is vital that the public has access to straightforward, responsible information about how essential vitamins and minerals work. Taking supplements 'whenever they remember' isn't the most effective way of benefiting from them."

Industry

The HFMA is the trade association for the UK's natural health industry. A not-for-profit organisation, it represents more than 120 manufacturers and suppliers of quality natural health products.

The group said that the fruit most people preferred were bananas, and carrots came in as top vegetable.

Not taking the right amount of nutrition in your diet can lead to malnutrition.

According to a report published by the British Association for Parenteral and Enteral Nutrition (Bapen), treating this undernourishment in hospitals, care facilities, GP's clinics and in the community cost the UK more than £7.3 billion each year, more than double the estimated £3.5bn cost of tackling obesity.

Malnourished individuals stay in hospital longer, succumb to infection more often, visit their GP on more occasions and require longer, more intensive, care than individuals who are adequately nourished.

Indeed, HFMA's survey is not the first to reveal the shocking state of the nation's diet.

In November, Bapen found some 25 per cent of patients admitted to hospitals and care homes were at risk from malnutrition.