It’s been called “deadly,” “toxic,” and “poison”. Today there’s no shortage of books, news articles, and journal articles singling out the sweet substance as the scapegoat for all of society’s ills. These include obesity, metabolic syndrome factors such as high blood pressure, non-alcoholic fatty liver disease (NAFLD), type-2 diabetes, and cardiovascular disease.
Providing the most recent fodder for anti-sugar headlines in several media channels was the World Health Organization (WHO) recommendation to halve intake of sugar in draft guidelines released on March 5 for public consultation (now closed). It provided strong recommendations to reduce intake of free sugars and to limit intake of free sugars to less than 10 percent of calories per day, as well as a conditional recommendation to further reduce free sugars to below 5 percent of calories for additional benefits for body weight and dental caries.
But what does the evidence really say about sugar’s impact on health to warrant such low doses? How does it really compare with other sources of carbohydrates and calories in foods and beverages? And, is the focus on fructose as a monosaccharide warranted in finding a real answer to improving public health? Challenging the WHO and others for spreading fears about sugar unfairly were scientists in a symposium on Saturday, April 26. The event, supported and sponsored by the Corn Refiners Association, took place during the American Society for Nutrition 2014 Scientific Sessions and Annual Meeting at Experimental Biology in San Diego.
Dr. John Sievenpiper, of St. Michael’s Hospital in Toronto, compared all the attention surrounding sugar to that of fat consumption in the 1950s. Like with fat in those earlier years, he said it’s difficult to separate out how fructose-containing sugars contribute to obesity and cardiometabolic disease. A lot of the reason is due to small effects and lack of demonstrated harm of sucrose, high-fructose corn syrup, or fructose over other sources of excess calories in the diet.
“There are many pathways to overconsumption leading to weight gain,” Dr. Sievenpiper said. “Attention needs to remain focused on reducing overconsumption. We need to get away from a single nutrient approach and focus on total diet and dietary patterns to improve health.”
When interpreting results of trial designs relating to sugar, Dr. Sievenpiper said, it’s important to “follow the energy.” For example: Isocaloric or “substitution” trials are those where energy from sugars are substituted for other sources of energy in the diet; hypercaloric or “addition trials” are where energy from sugars are added to the diet; while hypocaloric or “substraction” trials are where energy from sugars are substracted from the diet.
It shouldn’t be surprising that the addition of excess energy from sugars in hypercaloric trials would lead to increased weight gain. There is consistent evidence, Sievenpiper said, that hypercaloric feeding of sugar and fructose promotes weight gain, fasting and postprandial dyslipidemia, raised uric acid levels, and NAFLD. But these effects all are attributable to the excess energy rather than the fructose itself.
The WHO draft recommendations, Dr. Sievenpiper pointed out, were based mainly on evidence that addition of excess energy from sugars increased body weight, which reinforced their current recommendation of 10 percent (Morenga et al 2013). But the recommendation to reduce sugar intake to less than 10 percent and, further, to 5 percent was solely based evidence in reduction of dental caries (Moynihan and Kelly 2012).
On the other hand, Dr. Sievenpiper cited the work of Sigrid Gibson and colleagues showing that a moderate dietary sucrose intake at levels up to 25 percent of energy appear to have no significant adverse effects on metabolism when substituted for starch, at least in the medium term.In addition, reviews published by Dr. Sievenpiper’s lab using controlled feeding trials with fructose at low to moderate doses (in doses normally found in fruit) does not harm body weight, serum fasting or postprandial lipids, uric acid, and NAFLD. At these levels in humans, he said, the evidence even suggests a benefit to blood pressure and glycemic control.
Fructose-Fatty Liver Hypothesis
One of the major sources of controversy surrounding fructose is that because, unlike glucose and other sugars, it’s metabolized primarily by the liver. This fact along with evidence from animal trials has led to concerns that fructose may have a greater likelihood of being converted into fat through de novo lipogenesis. However, Luc Tappy and Kim-Anne Le previously demonstrated that generally less than 3 percent of fructose ends up being converted to fat in typical diets, while the rest ends up burned up as energy or stored as liver glycogen in humans.
But this evidence hasn’t kept the belief that fructose is uniquely harmful from reaching the mainstream, largely because of perpetuation by Dr. Robert Lustig (and his famous YouTube video), as well as others, who have championed the idea and have even likened fructose to ethanol and suggested it contributes to NAFLD. These misguided views are “becoming doctrine,” Dr. Sievenpiper said. And it can lead to confusion about whether or not fruits, which contain varying levels of fructose, should be avoided.
Through a systematic review of published literature, Mei Chung, Ph.D., a research assistant professor at Tufts University School of Medicine, sought to evaluate the effects of different levels and forms of dietary fructose on the incidence or prevalence of NAFLD and on indices of liver health in humans.
Chung provided a summary of the evidence that included five observational studies and 19 interventional studies that investigated a variety of clinical outcomes. The study found that both hypercaloric fructose and glucose diets (excess energy) had similar effects on liver fat and liver enzymes in healthy adults. She said there was “insufficient evidence to draw a conclusion” on liver de novo lipogenesis from the limited amount of intervention studies.
“Based on the indirect comparisons across study findings, the apparent association between indices of liver health and fructose or sucrose intake appear to be confounded by excessive energy intake,” Chung said. She expects the full findings to be published in a peer-reviewed journal soon.
Roger Clemens, DrPh, chief science officer of E.T. Horn, discussed matters of policy surrounding sugar intake. He highlighted that there were global efforts to reduce prevalence of obesity through approaches in dietary guidelines, taxation on sugar-sweetened beverages, and restricted access to these products. Approximately 60 countries now recommend limiting intake of added sugar and sugar-sweetened beverages in diverse ways, he said. But these efforts have inconsistent results relative to changes to body weight in targeted populations.
Clemens also warned that what’s driving the policy is epidemiological evidence that can’t establish causation, while the evidence from randomized controlled trials is largely being ignored, although they show that when sugars are isoenergetically exchanged with other carbohydrates they are not associated with weight change. “What evidence do you want to accept?” he charged.
Criticizing the proposed changes to nutrition facts panels by the U.S. Food and Drug Administration, Clemens also said listing “added sugars” was wrong-headed. “It’s silly and impractical,” he said considering that there are no analytical methods for added sugars, so food producers would have to provide information and maintain records for two years.
There are really no signs that suspicions about sugar are abating among the public. The belief that sugar is “addictive” (similar to illicit drugs) is now becoming pervasive. The major challenge for the scientific community, Clemens said, is how to get the word out about evaluating topics like sugar through the lens of evidence. Through social media, the public has been largely sold that sugar is uniquely harmful, he said. “How can we compete?”
Part of the reason why sugar remains in the spotlight is that “it’s a low hanging fruit,” Dr. Sievenpiper said after the event. He also hedged that by no means does he advice against limiting amounts of sugar or sugar-sweetened beverages in a person’s diet, so long as it’s part of a total dietary pattern designed to yield results in terms of reducing overall energy intake.
It’s advice reminiscent of the old adage of “losing sight of the forest from the trees”—demonizing one nutrient distracts from the overall dietary pattern (with many contributing factors) that deserve attention.