The FSA also discourage 'supersize' chocolate bars
Manufacturers are being asked to cut the size of chocolate bars, confectionery and cans of fizzy drink to tackle rising rates of obesity.
By 2012, the Food Standards Agency wants chocolate-based snacks such as Mars bars to be no bigger than 50g compared with the current 58g size.
Bars of chocolate should be no larger than 40g, a draft consultation warns.
Industry representatives said they were disappointed by continued moves to set "arbitrary targets".
The voluntary proposals also call for manufacturers to reduce the amount of saturated fat and added sugar in biscuits, cakes, pastries, chocolate confectionery and soft drinks.
A report from the FSA said there had been some progress - such as moves by United Biscuits to cut saturated fat in Digestives, Hob Nobs and Rich Tea biscuits by 50%.
Tesco was also highlighted for removing 110 tonnes of saturated fat from its cakes by the end of 2008.
But when it comes to chocolate bars, EU rules restrict sugar and fat reductions, making reformulation difficult, the FSA said.
Reductions are however possible through cutting portion sizes, it added.
Chocolate bars, such as Dairy Milk and Yorkie, including those with added fruit and nuts, should weigh no more than 40g, the FSA said.
And chocolate products with "fillings" such as Mars bars, Twix and Snickers, should weigh no more than 50g and their saturated fat content be cut by at least 10%.
HAVE YOUR SAY
How does the size of the bar matter - folks will buy two if they don't get the kick they want
Cans of fizzy drinks should be cut from 330ml to 250ml by 2015, the FSA recommended.
And single portions of sugar-containing still and juice drinks should also be no more than 250ml.
On current trends around 60% of Britons will be obese by 2050.
Health problems associated with obesity already cost the NHS £4.2bn a year, a figure that is set to double by 2050.
Almost nine out of 10 children aged seven to 14 drink fizzy drinks and 34% of 11-16 year-olds consume chocolate at least once a day, figures show.
CURRENT CHOCOLATE SIZES
Mars bar 58g
Kit Kat Chunky 50g
Dairy Milk 49g
Gill Fine, director of consumer choice and dietary health at the FSA, said they recognised the achievements already made by some manufacturers.
"But to make even greater progress it's important that everybody gets behind our recommendations on saturated fat, added sugar and portion sizes.
"What we are not doing is telling people what to eat.
"What we want to do is to make it easier for people to make healthier choices - to choose foods with reduced saturated fat and sugar - or smaller portion sizes."
Julian Hunt, director of communications at the Food and Drink Federation, said manufacturers had been working on cutting sugar and fat in their products for a number of years but there were significant technical, financial and consumer challenges that companies have to overcome.
"Policy makers need to be realistic about the pace at which our members can be expected to keep delivering new innovations - particularly in the current recession," he said.
He added that they were committed to working with the FSA but reformulation was just one option.
"We are disappointed that it appears to remain committed to setting arbitrary targets for specific nutrients in certain foods, rather than focusing on the need for everyone to achieve a balanced diet and lifestyle."