Trendy low-carb diets received a drubbing yesterday from health officials, who said carbohydrates should form the backbone of a healthy diet.

Meals that are low in carbohydrates do not provide vital nutrition because they lack the fibre crucial for digestion, Public Health England said.

It updated its healthy eating advice to urge Britons to consume more potatoes, pasta, bread and other starchy carbohydrates to increase fibre intake by more than half - from 19g a day to 30g a day.

So, in addition to five portions of fruit and veg a day, people need the equivalent of two wholemeal breakfast cereal biscuits, two thick slices of wholemeal bread and a large jacket potato with its skin. But the experts said it was important to choose wholegrain options to get the most nutrition from carbohydrates.

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The Eatwell Guide increases the amount of starchy carbohydrates from 33 to 37 per cent of recommended daily intake.

Officials also warned that people should no longer rely on supposedly healthy "juicing" diets for their nutrition. Fruit juices and smoothies should be limited to a single 150ml glass a day because they are packed with sugar and rarely include much fibre.

A spokesman said: "There seems to be a juicing trend, and low-carb diets are popular, but the scientific evidence is telling us otherwise."

Fibre helps the body digest food, as well as keeping people feeling fuller for longer. It is also known to protect against certain cancers, heart disease and diabetes. One in nine cases of bowel cancer is linked to eating too little fibre.

Sian Porter, of the British Dietetic Association, said: "You still need to watch your portion size, but starchy carbohydrates should form the basis of any diet."

The guide also urges Britons to eat less cake, biscuits and sweets, red and processed meat, and dairy. However, Terry Jones, of the Provision Trade Federation, told Farmers Weekly this was a "kick in the teeth" for hard-pressed dairy farmers.

He added: "I find it staggering that, at a time when ministers are expressing support for the sector, an agency of government should not only encourage consumers to reduce consumption of dairy products, but also seemingly ignore the positive role they can play in public health."