Food manufacturers have been accused of making misleading claims about how their products can improve health.
The Consumer's Association wants clearer labels
According to the Consumers' Association, many claims are based on scant evidence or are just wrong.
It follows a review of a number of popular foods by three nutritionists for the association's Which? magazine.
They looked at products claiming to count towards the recommended five portions of fruit and veg a day and others claiming to boost the heart.
According to Which?, some products which make these claims fail to live up to their promises.
In some cases, this is because they contain other ingredients that are not good for health.
For instance, Heinz spaghetti in tomato sauce claims to contain the equivalent of one portion of fruit and vegetables per can. The tomato puree in the spaghetti counts as one portion.
But according to Which? the product would not meet government criteria because it contains too much salt.
A spokesman for Heinz said it stood by its claims: "Our five-a-day scheme was drawn up with the British Dietetic Association. We completely stand by the claims."
The supermarket chain Sainsbury's came in for similar criticism. It claims its five fruit smoothie contains the equivalent of two portions of fruit and vegetables.
But according to the Department of Health juices and smoothies can only count as one portion per day.
A spokeswoman for Sainsbury's said the claims were based on the size of the smoothies.
"We use the 80g measure as a portion size. Unlike fruit juice where 150ml is one portion, all Sainsbury's 300ml 'Way to 5' smoothies contain fibre from fruit juice, puree and pulp equivalent to 160g of fruit which constitutes two portions as indicated on the label," she said.
Other products make claims for which there is no evidence, according to the Which? report.
It highlighted a vitamin drink called Optio Tone, which claims to help maintain healthy skin, saying they have no scientific basis.
Patrick Holford, of the Institute for Optimum Nutrition, who helped to develop the drink dismissed the claims.
"They haven't looked at studies. The levels of nutrients in Optio Tone are based on scientific studies based on optimum skin health," he said.
Helen Parker, editor of Which?, said clearer rules are needed.
"We'd like to see mandatory labelling of nutrients on all pre-packaged foods. The government and the Food Standards Agency need to provide clearer nutrition advice to help us work out the truth behind the labels."
The Food and Drink Federation said manufacturers make claims to help customers and do not mislead.
"UK food and drink manufacturers rely on the trust and loyalty of their customers and in no way set out to mislead," said a spokeswoman.
"In fact, the 1990 Food Safety Act already protects consumers by stating that 'marketing claims and labelling should be truthful, accurate and not misleading'.
"FDF and individual manufacturers promote the five a day message to inform consumers that they can achieve this goal through a variety of raw and processed foods."