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Dietary guidelines relating to sugar -- all of which recommend significant reductions in sugar intake -- are based on weak evidence and are not trustworthy, according to a systematic review published in Annals of Internal Medicine.
But an accompanying editorial points out that the systematic review is itself not trustworthy, since it was funded by an organization supported by the food and beverage industry.
The review authors, led by Bradley C. Johnston, PhD, of the Hospital for Sick Children Research Institute in Toronto, identified and scrutinized nine guidelines, including those from the U.S. Department of Agriculture and the World Health Organization. The conclusion: methodologies used to develop the guidelines had "major limitations" and that their recommendations, including reducing sugar intake, were supported by evidence of "low to very low" quality.
"All of the reviewed guidelines suggested a decrease in consumption of nonintrinsic sugars," the authors wrote. "Although the overall direction was consistent, the rationale and evidence used to make each recommendation were inconsistent. This lack of evidentiary consistency, with various health concerns cited, creates confusion for practitioners and the public about the role that sugar plays in health."
Johnston and colleagues emphasized that they were not saying sugar is harmless. "Sugar added to products adds considerable calories without any nutritional benefits and may take the place of other nutrient-dense foods in the diet," they wrote, noting that reducing consumption "at a population level may result in a reduction in caloric intake and a subsequent decrease in the rate of overweight and obesity."
Rather, they argued that the evidence base remains too spotty and tainted by interest groups. What is needed, they said, was more rigor, more transparency, and more specificity in the dietary recommendations. "At present, there seems to be no reliable evidence indicating that any of the recommended daily caloric thresholds for sugar intake are strongly associated with negative health effects," they argued.
But the organization that funded the study, the North American branch of the International Life Sciences Institute (ILSI), is itself funded by Coca-Cola and other soda and candy manufacturers.
"In essence, this study suggests that placing limits on 'junk food' is based on 'junk science'," wrote Dean Schillinger, MD, and Cristin Kearns, DDS, MBA, of the University of California San Francisco in an accompanying editorial.
"Similar claims were made by the tobacco industry in its attempt to discredit evidence on the harms of tobacco," they observed.
In response to the claim that the different guidelines are inconsistent, they noted that the guidelines were produced over more than 20 years, and that the more recent guidelines "show remarkable consistency." They called the Annals review "an example of the 'politicization of science'" citing other ILSI activities in defense of the interests of food and beverage companies. They recommend that journals should "refrain from publishing studies on health effects of added sugars funded by entities with commercial interests in the outcome."
Dietary guidelines have been the subject of considerable controversy. The latest update of the USDA guideline came under fire in a BMJ investigation by journalist Nina Teicholz, a well-known advocate of low-carb diets. Her claim that the USDA guideline was biased against saturated fats itself became the subject of intense criticism from the nutritional mainstream supporting the USDA.
Teicholz and the Annals authors are on opposite sides of the sugar debate, but Teicholz said she agrees with the Annals authors that dietary guidelines "are not based on systematic, comprehensive reviews of the most rigorous science." She said that guidelines should "be based on strong science; otherwise, they're open to bias and group think -- as we've seen with the recommendations on fat and cholesterol, which then had to be reversed. The historical evidence certainly points to sugar as a prime suspect in causing nutrition-related diseases, but if the government is going to make a policy on this issue, then it should to do the rigorous clinical trials needed to provide the necessary evidence."