Cutting out added sugar from one's diet can result in weight loss, reduced blood pressure and improved insulin sensitivity, according to a new study by researchers at University of California, San Francisco, and Touro University.
The fascinating experiment, which swapped out added sugar in children’s diets for starchy foods -- in effect, swapping fructose for glucose -- hammers another nail into the coffin of the phrase, “a calorie is a calorie,” the researchers claim. Instead, it suggests that added sugars are exacting a unique toll on people’s bodies by making them prone to hypertension, diabetes and obesity, and that simply switching added sugars for starchy foods of equal caloric value results in better health.
“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 principal researcher Robert Lustig, a pediatric endocrinologist researcher at UCSF, in a statement.
However, critics of the study say that the sugar-free diet worked so well that the children lost too much weight, muddling any conclusions about why their health took a turn for the better. Was it really the lack of sugar that did it, or was it the weight loss?
How the kids cut sugar out
To see whether added sugar played a role in health, the researchers recruited 43 obese black and Latino children who also showed signs of an impending chronic illness, such high blood pressure or hyperinsulinemia, which is linked to Type 2 diabetes. Then they asked the children questions about their normal diets at home to figure out what things they were eating, how many calories they consumed, and how much protein, fat and carbohydrates they were ingesting.
Then, for nine days, the children ate a catered version of their diets created by the researchers. These catered meals and snacks matched their normal home diets calorie for calorie, and included the same proportion of protein, fat and carbohydrates. The only difference was that added sugars in the meals were replaced with starches. Practically, this meant swaps like bagels for pastries, baked potato chips for yogurt, and turkey hot dogs for chicken teriyaki. However, the children were allowed to continue eating whole fruit, which is another -- albeit much healthier -- source of fructose.
These food swaps lowered added sugar from 28 percent of the children's daily calories to 10 percent, the level recommended by the World Health Organization. And to make sure that the children didn’t lose weight -- the researchers wanted to test the effect of the food swap, not any resulting weight loss -- they were also instructed to weigh themselves every day and to eat more food if necessary.
The kids took to the diet very well, Lustig told The Huffington Post. All but one of the children thought the new diet was yummy (the clinical word was “highly palatable”), and, despite the children’s efforts to keep their weight steady, they couldn’t eat enough to prevent weight loss. Over the nine-day experiment, they lost an average of two pounds even though most of the children said they were too full to eat more food.
Jean-Marc Schwarz of Touro University California hypothesized that the lack of sugar helped the children recognize when they were full and hungry.
"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,” Schwarz said in a statement. "Some said we were overwhelming them with food."
Improved health all around
In addition to improved satiety cues and weight loss, the kids’ blood pressure dropped an average of five points along with their fasting glucose -- the levels that indicate whether a person has normal blood sugar, pre-diabetes or diabetes. Their liver function improved, their triglycerides levels dropped 33 points, and the LDL levels, or bad cholesterol, dropped by 10 points. Their insulin levels decreased one-third.
"In sum, virtually all aspects of their metabolic health improved,” wrote Lustig. "These indicate that these children improved their metabolic status in just 10 days, even while eating processed food, by just removing the added sugar and substituting starch."
Previous studies on the health effects of sugar have added more of it to people’s diets to see if it make them sicker (it does). Other researchers, approaching the issue like a chicken vs. egg debate, have speculated that it’s a person’s obesity, not their diet, that puts them at higher risk of chronic disease. Lustig wanted to see if removing added sugar from the diet actually made people healthier. But Susan Roberts, a nutrition professor at the USDA Nutrition Center at Tufts University, says the fact that the children lost an average of two pounds in nine days confounds the results so much that it’s possible, and perhaps likely, that their improved health markers were the result of weight loss — not the lack of fructose.
“Confounded nutrition studies are ten a penny, and we should not bamboozled by inflammatory claims build on confounded data.”
"We know that a healthy diet and weight loss cause good metabolic changes, and although this study tries to attribute its effects to low fructose, in fact it is impossible to do that because of the study design,” Roberts told HuffPost. "Confounded nutrition studies are ten a penny, and we should not bamboozled by inflammatory claims build on confounded data."
Roberts said there were serious flaws in its methodology. Besides the fact that the children lost weight, their catered experimental diet was based on the children’s self-report of what they eat. Self-reporting one’s own diet is notoriously inaccurate, she pointed out, and past research shows overweight children tend to underestimate what they eat. In this case, Roberts said, who’s to say that the children weren’t simply eating less overall calories than they normally did?
"I really don’t think you can say much from this study except that weight loss with a healthy diet is healthy,” Roberts concluded.
Lustig said he anticipated this criticism, which is why he set out to do an “isocaloric” study in the first place. But because the children couldn’t keep their weight on, Lustig and the other researchers took pains to measure one more thing: their body composition, before and after. The results showed that most of the children’s weight loss was due not to fat loss, which would have produced such metabolic improvements, but water or muscle weight, which should have made their metabolic health worse.
Finally, in what’s called a “sensitivity analysis,” the researchers also isolated a subgroup of ten children who did not lose any weight at all, and showed that their health markers improved as well.
“The sensitivity analysis shows that even those who gained weight still improved their metabolic markers,” Lustig wrote to HuffPost. “That means that the improvement in their metabolic health was not due to any weight loss."
As for the catered diet, Lustig pointed out that baseline levels of self-reported sugar don’t need to be accurate, because the interventions all had the same goal: to bring added sugar levels down to about 10 percent of their daily calories.
Easy food swaps, dramatic health changes
While researchers obviously don’t agree on what caused the children’s metabolic health to improve, it is intriguing that a simple, relatively easy ingredient swap seemed to produce weight loss and improved metabolic health in children -- all while keeping them full and happy.
After all, how hard is it to swap in a bagel for your usual morning pastry? Food for thought!
The study was published online Tuesday in the journal Obesity.
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