* Draft guideline suggests adult limit of 6 teaspoons a day
* Poor diets linked to obesity, tooth decay, chronic disease
* WHO expert "more intense action" needed on sugary drinks (Adds quotes, details from press briefing)
By Kate Kelland, Health and Science Correspondent
LONDON, March 5 (Reuters) - Adults should eat less than the equivalent of 6 teaspoons of sugar a day if they are to avoid health risks such as weight gain and tooth decay linked to sugary diets, the World Health Organisation said on Wednesday.
Issuing draft guidelines calling for a new sugar limit of less than 5.0 percent of daily energy intake, the United Nations health agency said its recommendations were based on "the totality of evidence regarding the relationship between free sugars intake and body weight and dental caries".
"Obesity now affects half a billion people in the world, and it is on the rise in all age groups and particularly in low- and middle-income countries," said Francesco Branca, the WHO's director of nutrition for health and development, adding that free sugars were a key culprit in that epidemic.
Free sugars include monosaccharides and disaccharides that are added to foods by manufacturers, cooks or consumers, and sugars naturally present in honey, syrups, fruit juices and fruit concentrates.
Five percent of total energy intake is equivalent to around 25 grams - or around 6 teaspoons - of sugar a day for a normal weight adult.
"WHO recommends reduced intake of free sugars throughout the life-course," the agency said in a statement.
It said the 5.0 percent level should be a target for people to aim for - calling it a "conditional recommendation" - but also reiterated a "strong recommendation" that sugar should account for no more that 10 percent of total energy intake.
"There is increasing concern that consumption of free sugars - particularly in the form of sugar-sweetened beverages - increases overall energy intake and may reduce the intake of foods containing more nutritionally adequate calories," it said.
This can lead "to an unhealthy diet, weight gain and increased risk of non-communicable diseases (such as heart disease, diabetes and cancer)."
Non-communicable, or chronic, diseases are the world's leading causes of ill health and death, killing more than 36 million a year with more than 90 percent of these premature deaths in poorer countries.
Asked whether he would characterise sugar as "the new tobacco" in terms of its threat to public health if consumption levels are not reduced, Branca said sugar was one key risk factor which, combined with others like fat, salt and lack of exercise, could be compared to smoking.
Research published last month in the journal JAMA Internal Medicine suggested the risk of dying of heart disease is higher among people who eat a larger percentage of their calories from added sugars. And the risk was also higher for people who had seven or more sweetened drinks a day.
"The consumption of sugar-sweetened beverages has to be done with great care - particularly in children," Branca said. "This is an area where more intense action needs to be taken."
Branca acknowledged the new guidelines "may not be popular amongst sugar producers" but said the WHO would resist any unjustified pressure or lobbying from the food and sugar industries to change them.
"If pressure comes on the organisation we are very well equipped to deal with (it)," he said. "I don't anticipate any problem in that regard." (Reporting by Kate Kelland, editing by Ralph Boulton)