Slimmers struggling to control their junk food cravings may be able to enjoy a few more fatty or sugary treats without guilt, as the calorie counts used as the basis for diets and healthy-eating guidance for the past 18 years could be wrong.

A draft report by the Scientific Advisory Committee on Nutrition (SACN), which advises the government, recommends that adults' recommended daily calorie intake – currently 2,000 for woman and 2,500 for men – could be increased by up to 16%.

This means men could safely consume an extra 400 calories a day, equivalent to an average-sized cheeseburger or two bags of ready salted crisps.

The revised guidance [pdf] comes after researchers found a more accurate assessment of how fat can be burned off through exercise. But the committee, which includes some of Britain's top nutritional experts, said people should only eat more if they exercise more, given rising levels of obesity.

Health campaigners and consumer experts fear the revised figures could send out the wrong message to people who are overweight.

Ministers are already considering the introduction of new food-labelling schemes to highlight the calorie content of foods relative to guideline daily amounts (GDAs).

Existing guidelines on daily calorie intake for good health have formed the basis of food labelling and dietary advice from doctors and nutritionists since 1991. If the committee's proposals are accepted, some foods would be upgraded to a healthier rating.

A third of all British adults, or 13 million people, will be obese by 2012 if current trends continue. The committee's suggestions are subject to a 14-week consultation before final recommendations are made.