Are all sugars created equal, or are some more likely to cause obesity and related diseases, including type 2 diabetes?
A study published in the American Journal of Clinical Nutrition in 2004 proposed that the growing use of high-fructose corn syrup as a sweetener in processed foods could be linked to ballooning rates of obesity. It launched a long, contentious scientific debate.
A recently published paper in the Mayo Clinic Proceedings won’t settle the issue, but it does pose a significant new challenge to those who believe that a sugar is a sugar is a sugar. The comprehensive literature review claims to show for the first time that, calorie for calorie, added sugars — especially fructose — are more damaging to the body’s metabolic systems than other carbohydrates and are more likely to lead to type 2 diabetes and obesity.
Forty percent of all American adults have “some sort of insulin resistance,” said James DiNicolantonio, PharmD, an associate editor at BMJ Open Heart, who co-authored the paper with Dr. Sean Lucan of the Albert Einstein College of Medicine.
The paper argues that the most current guidelines for how much added sugar is safe to eat are grossly exaggerated. It suggests that just 5 to 10 percent of our total caloric intake should come from added sugar. That comes out to about 22 grams of sugar — about half as much as a single can of soda.
How Is Fructose Different?
Why fructose, and why added sugar? All carbohydrates contain glucose. Some foods, notably fruits, also contain fructose. Fructose is sweeter than glucose, so it’s most often used as an added sugar in processed foods, whether in the form of high-fructose corn syrup or just plain old sugar.
Scientists call plain old sugar sucrose, and it’s a 50-50 mix of fructose and glucose. High-fructose corn syrup is cornstarch — glucose — with enzymes added to convert some of the glucose into fructose. The sweetener contains around 55 percent fructose.
The new study — drawing on clinical trials, basic science, and animal studies — concludes that fructose is more damaging to health than glucose.
Lucan and DiNicolantonio lay out a series of findings that show the digestive tract doesn’t absorb fructose as well as other sugars. More fructose then goes into the liver. Too much fructose in the liver eventually creates a cascade of metabolic problems that includes fatty liver disease, systemic inflammation, type 2 diabetes, and obesity.
This issue has been hotly debated, since many say that metabolic problems including diabetes, prediabetes, and obesity stem from eating too many calories, period, or too many calories from sugar regardless of the type.
Fred Brouns, Ph.D., a nutrition professor at the Maastricht University in the Netherlands, has published studies on fructose metabolism. He doesn’t think the evidence supports a claim that the fructose found in a typical American diet deserves to be singled out. It’s never eaten in isolation, for starters.
“Fructose can be detrimental, correct, but only in excessive amounts that are not consumed by the majority of the population. It is unrealistic to put the finger to sugars alone and certainly not to fructose in isolation,” he said in an email.
Michael Goran, Ph.D., a professor of preventive medicine and physiology at the University of Southern California, who has also published papers on fructose, does see fructose as especially harmful, but he admitted that sugar is a “contentious field.”
“If you called 10 people, five people will agree and five will say it’s just about calories,” he said.
The findings will almost certainly bring a heated rebuttal from the food industry. The Corn Refiners Industry pointed Healthline to Dr. James M. Rippe, who is funded in part by ConAgra Foods. Rippe called the paper “more of a diatribe than a research article.”
A Hierarchy of Sugars
Fructose is a hot topic, but scientifically and practically speaking, the study’s bigger finding is that all added sugar is more damaging than sugar naturally found in foods. That includes cane sugar and even the honey and maple syrup that some health-conscious shoppers prefer over corn syrup.
“Our review is one of the first to comprehensively say absolutely sugar is worse than other types of carbohydrates,” said DiNicolantonio.
How can the body tell the difference? In addition to the presence of fructose in added sugars, there’s the absence of fiber to slow digestion and phytochemicals to protect the body from the damage high glucose levels can do, DiNicolantonio explained.
“There’s a hierarchy: starch, sucrose, which is half fructose, and then fructose,” Goran said.
Here’s why. A soda has about as much sugar as three or four oranges. If the soda is, like most, sweetened with high-fructose corn syrup, about 10 percent more of that sugar is fructose, which is harder on the body. And unlike the soda, oranges include fiber, which slows down the rate at which the sugars are digested, and phytochemicals that counteract inflammation.
It would also take quite a bit longer to eat four oranges, and the speed of ingestion can help overwhelm the body’s ability to process sugars.
So where does that leave juice? It’s not much better than soda, according to Goran.
“Fruit juice would be an example of something that the population wouldn’t think of as a sugary drink and might even have some positive valence in terms of health messaging, but it’s actually just as high in sugar,” he said.
Negotiating Nutrition Labels
Other than steering consumers away from fruit juice, the dietary advice the study offers is not much different from what we’ve been hearing. Control calories and eat less sugar.
But how can consumers tell the difference between added sugar and naturally occurring sugar based on a nutritional label?
“That’s tricky,” said DiNicolantonio. “One way is to look at the list of ingredients.”
Ultimately, eating better, all agree, means eating fewer processed foods.
DiNicolantonio said the takeaway is first to ensure that we’re within recommended caloric limits, then to avoid added sugar and eventually to reduce how much processed food we eat.
“My advice for patients is to go for something that doesn’t have any [added] sugar, and you can add a little bit of honey or syrup. At least then you’re balancing sugar with good taste. Nobody’s drinking a bottle of honey or a bottle of maple syrup,” Goran said.
Brouns’ bottom line is hardly different.
“Consumers should eat more fresh foods and increase the amounts of fruits, vegetables, legumes, and whole grains,” he said.
Goran agreed. “Really the message is to avoid processed foods,” he said.