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."