Researchers found that while most low-fat supermarket products contain a third fewer calories than their regular-fat versions, 10 per cent actually contain more or the same calories, mainly due to added sugars.
Asda natural low-fat yoghurt had more calories than Asda natural yoghurt; Birdseye light and crunchy breaded chicken had more calories that Birdseye crispy chicken; and Sainsbury’s low-fat custard had the same calories as Sainsbury’s custard.
WeightWatchers wholemeal thick-slice bread had more calories than any own-label wholemeal thick-slice bread, while WeightWatchers sliced cheese had more calories than any own-brand sliced cheese.
The one example where the low-fat version had more fat than the normal version was Asda own-brand low-fat Italian dressing.
The research by Dr Matthew Capehorn, of the Rotherham Institute for Obesity, and other colleagues, set out to establish whether low-fat versions of products were nutritionally healthier, mainly in terms of sugar and overall calories.
Of the ten most popular UK supermarkets, four provided online nutritional information sufficient to complete the study – Sainsbury’s, Asda, Waitrose and Tesco. At the end of November last year, their websites were analysed.
Fat, sugar and calorie content were recorded for any low-fat food that had a directly comparable regular-fat product made by the same brand.
Of 62 products that matched these criteria found in the four supermarkets, 56 low-fat products had fewer calories and, on average, the low-fat products had 31 per cent fewer calories overall. Dr Capehorn said: “Low-fat foods do appear on average to help reduce calorie intake and therefore may be encouraged as part of a weight-loss strategy.
“However, appropriate food choices may still require reading nutritional information on the food labels as 10 per cent of low-fat foods still have more calories, and 40 per cent have more sugar, than their regular fat counterparts.”
A Birdseye spokesman said: “Our light and crunchy breaded chicken is not marketed as a low-fat or low-calorie alternative to crispy chicken.
“The use of ‘light’ in the name refers to its taste and texture.”
Weightwatchers said it was redeveloping its wholemeal thick-sliced bread in light of the research. But WeightWatchers rebutted suggestions its sliced cheese had more calories than any own-brand equivalent. A spokesman said: “We believe the nutritional values quoted for cheese are incorrect.”