The findings, published in the journal Obesity, suggest that reducing consumption of added sugar, even without reducing calories or losing weight, has the power to reverse a cluster of chronic metabolic diseases including high cholesterol and blood pressure in children in as little as 10 days.
Led by Professor Robert Lustig from the University of California and Benioff Children's Hospital San Francisco, the study reports that after just 9 days on a sugar-restricted diet, virtually every aspect of the 43 participants' metabolic health improved, without change in weight.
"I have never seen results as striking or significant in our human studies; after only nine days of fructose restriction, the results are dramatic and consistent from subject to subject,” said the paper’s senior author Dr Jean-Marc Schwarz from Touro University California.
"This study definitively shows that sugar is metabolically harmful not because of its calories or its effects on weight; rather sugar is metabolically harmful because it's sugar," added lead author Lustig. "This internally controlled intervention study is a solid indication that sugar contributes to metabolic syndrome, and is the strongest evidence to date that the negative effects of sugar are not because of calories or obesity."
A note of caution?
Reacting to the study, Professor Tom Sanders of King’s College London warned that the fact that the trial was uncontrolled means that the claims need to be viewed with caution.
“As the study lacked a control group who remained on a high sugar diet, the claim that that sugar is more fattening than starch was actually not tested for,” noted Sanders. “Instead the comparisons were made with reports of ‘usual intake’. But it is well known that obese children underestimate and under-report food intake, particularly of soft drinks and snack foods.”
He added that in this case, a restriction in food energy intake would be expected to lower blood pressure, “and a restriction of carbohydrate intake would have favourable effects on insulin secretion and insulin sensitivity.”
Tracy Parker of the British Heart Foundation added that while the study is interesting, more research is needed to confirm the findings, while Professor Naveed Sattar at University of Glasgow said that even very modest weight loss such as that seen in the trial can lead to metabolic changes that can seem larger than they actually are.
Digging deeper in to the study
Lustig and his colleagues identified and recruited 43 children aged between 9 and 18, who were obese and had at least one other chronic metabolic disorder, through the Weight Assessment for Teen and Child Health Clinic (WATCH) at UCSF Benioff Children's Hospital San Francisco.
They noted that recruitment was limited to Latino and African-American youth because of their higher risk for certain conditions associated with metabolic syndrome, such as high blood pressure and type 2 diabetes.
In the study, the participants were given nine days of food, including all snacks and beverages. The study menu restricted added sugar (while allowing fruit), but substituted it by adding other carbohydrates such as bagels, cereal and pasta so that the children still consumed the same number of calories from carbohydrate as before, but total dietary sugar was reduced from 28% to 10%, and fructose from 12% to 4% of total calories, respectively.
The team noted that children were given a scale and told to weigh themselves every day, with the goal of weight stability, not weight loss – adding that when weight loss did occur (a decrease of an average of 1% over the 10-day period but without change in body fat), they were given more of the low-sugar foods.
"When we took the sugar out, the kids started responding to their satiety cues," commented Schwarz. "They told us it felt like so much more food, even though they were consuming the same number of calories as before, just with significantly less sugar.”
“Some said we were overwhelming them with food."
After nine days on the sugar-restricted diet, virtually every aspect of the participants' metabolic health improved, without significant change in weight or body fat, said the team.
On average, diastolic blood pressure decreased by 5mm, triglycerides by 33 points, LDL-cholesterol by 10 points, and liver function tests improved, said the team – who noted that fasting blood glucose went down by 5 points, and insulin levels were cut by one-third.
"All of the surrogate measures of metabolic health got better, just by substituting starch for sugar in their processed food -- all without changing calories or weight or exercise," said Lustig – who added that the findings demonstrate that 'a calorie is not a calorie.'
“This has enormous implications for the food industry, chronic disease, and health care costs,” he said.
The team concluded by noting that further studies are now needed to determine whether sugar restriction alone can impact metabolic syndrome in adults, and whether such effects are short-lived or long-term.
Published online ahead of print, doi: 10.1002/oby.21371
“Isocaloric fructose restriction and metabolic improvement in children with obesity and metabolic syndrome”
Authors: Robert H. Lustig, et al