Kids who cut processed sugar from their diets for just nine days had lower blood pressure, cholesterol and blood sugar — a finding that supports the idea that sugar itself is a major culprit in heart disease and diabetes, researchers said Tuesday.
And it suggests that it doesn't take long to reverse the harmful effects of consuming too much sugar.
The study's not meant to be the last word on the health effects of sugar, but it joins a growing body of evidence that suggests processed sugar itself can have a cascade of effects on the body.
While other researchers were critical of how the study was done, they said it does open some important questions about how sugar affects metabolism.
"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," said Robert Lustig of the University of California San Francisco, who led the study.
Lustig and Jean-Marc Schwarz of the College of Osteopathic Medicine at Touro University California ran their experiment on 43 obese Latino and black children aged 9 to 18 who also had high blood pressure, unhealthy cholesterol levels or signs of too much fat in their livers.
These are all symptoms of the metabolic syndrome, a cluster of measurements that show people are at high risk of heart disease, stroke and diabetes because of unhealthy weight, poor eating habits or a lack of exercise.
The kids were put on a restricted diet that kept in the junk food — they got bagels, pasta and pizza — but took out the added sugar from sodas, sweets and other foods. The team was careful to feed the children about the same number of calories as they usually ate in a day.
Each child got a supply of food that closely approximated what he or she normally ate, Schwarz said.
"This 'child-friendly' study diet included various no- or low-sugar added processed foods including turkey hot dogs, pizza, bean burritos, baked potato chips, and popcorn that were purchased at local supermarkets," they wrote in their report, published in the journal Obesity.
They reduced sugar in the diet from 28 percent of total calories to about 10 percent.
"We took away only the processed sugar," Schwarz said.
The effects were startling, they reported.
After nine days, blood pressure went down by an average of five points, the triglyceride measurement of cholesterol fell by 33 points, low-density lipoprotein (LDL or "bad" cholesterol) fell by 10 points, and blood sugar and insulin levels both fell, also.
"Despite intensive efforts to maintain each participant's body weight at baseline levels, weight decreased by (about two pounds) over the 10 days of intervention," the researchers wrote.
Plus, the kids said they felt less hungry. A third of them said they could not eat enough food to stop losing weight.
"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," Schwarz said.
"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."
Health officials routinely advise Americans to eat less processed sugar.
Losing even a little weight can quickly improve blood pressure, cholesterol and blood sugar levels, but even the kids who did not lose any weight had improved measurements, the team said.
"It was surprising to see that nine or 10 days of sugar restriction was so powerful to reduce some of those risk factors for diabetes and lipids," Schwarz told NBC News.
There are lots of reasons sugar can have a direct effect on weight and metabolism.
"There was no sugar rush," Schwarz said. "It's what I like to call the tsunami effect." All that sugar overwhelms the liver, which turns it directly into fat.
Studies suggest that it can cause the body to absorb extra sodium, perhaps causing it to retain water and raise blood pressure. Schwarz believe the small amount of weight that the kids lost may well have been water loss.
The researchers agree there are big holes in their study. There was no so-called control group - a group of similar kids whose diets were not changed. It was a short study and 43 people is a very small number.
But most experts say American kids — and adults — eat far too much sugar.
A study published last year showed that nearly a third of kids screened at pediatric clinics in Houston had unhealthy cholesterol levels by age 9 to 11.