Limit sugar intake to six teaspoons per day, study suggests

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Scientists have found more evidence to support a recommendation made by the World Health Organization (WHO) in 2015 that added sugar intake should be limited to six teaspoons per day.

In a study published in the medical journal The BMJ on Wednesday, researchers from China and the U.S. shared a laundry list of negative outcomes strongly linked with sugar consumption, including asthma, diabetes, obesity, heart disease, depression, some cancers and death.

"Our umbrella review showed harmful associations between dietary sugar consumption and a range of cardiometabolic diseases," the study's authors wrote, "especially weight gain, ectopic fat accumulation, obesity, and cardiovascular disease, which can largely be attributed to excessive consumption of fructose-containing sugars."

Doctors and scientists have known for decades that eating too much sugar can harm your health in a variety of ways.

That knowledge led the World Health Organization to recommend reducing free sugar intake to less than 10 per cent of total daily energy intake for the first time in 1989. In 2015, the organization updated the guidelines again to recommend a further reduction to around five per cent, which is equivalent to about six teaspoons of sugar per day.

Free sugars, also known as added sugars, include glucose, fructose, sucrose or table sugar added to foods and drinks by the manufacturer, cook or consumer, as well as sugars naturally found in honey, syrups, fruit juices and juice concentrates. These sugars are also often "hidden" in processed foods that might not seem like an obvious source, such as ketchup, a tablespoon of which can contain a teaspoon of added sugar.

When the WHO made its six-teaspoon recommendation in 2015, evidence to support the recommendation was limited and much of it came from studies that hadn't been closely scrutinized for quality, accuracy and consistency. So the organization made the recommendation "conditional."

Now, thanks to the researchers behind the latest BMJ study, experts have the data they need to make a firm recommendation.

The team reviewed 73 meta-analyses – including 67 of meta-analyses observational studies and six of randomized controlled trials – from 8,601 articles covering 83 health outcomes in adults and children. A meta-analysis is a statistical analysis that combines the results of multiple scientific studies to look for large-scale trends.

They found "significant harmful associations" between added sugar and glandular and metabolic outcomes including diabetes, gout and obesity; cardiovascular outcomes including high blood pressure, heart attack and stroke; and cancer outcomes including breast, prostate and pancreatic cancer.

"Finally, harmful associations existed between dietary sugar consumption and all-cause mortality, asthma in children, attention-deficit/hyperactivity disorder, bone mineral density, dental decay and erosion, depression (and) non-alcoholic fatty liver disease," the authors wrote.

They also found that sugary drinks, such as soda, juice and sports and energy drinks, are the largest source of added sugars in many people's diets, and recommended limiting sugary drinks to less than one serving per week.

Because their findings were mostly informed by data from observational and low-quality studies, the authors said scientists will need to conduct more randomized, controlled trials to better understand the connections between sugar and specific diseases. But the overall message is clear.

"High dietary sugar consumption is generally more harmful than beneficial for health, especially in cardiometabolic disease," they wrote.

"Evidence of the association between dietary sugar consumption and cancer remains limited but warrants further research."