A large body of evidence from animal studies and observational and clinical trials in humans suggests that eating processed foods with added sweeteners is contributing to the growing incidence of type 2 diabetes, a new review, published online January 29 in the Mayo Clinic Proceedings, concludes.
This "is the first comprehensive literature review showing that even when keeping calories the same (ie, isocaloric exchange of starch for sugar), sugar is worse at promoting diabetes and the associated morbidity (neuropathy, nephropathy, retinopathy) and premature mortality," lead author Dr James J DiNicolantonio (Saint Luke's Mid America Heart Institute, Kansas City, Missouri) told Medscape Medical News.
Thus, "by limiting sugar to 5% to 10% of total caloric intake, the harmful effects of sugar, particularly fructose, on insulin resistance could be minimized," he and his colleagues conclude. This in turn "may protect against diabetes and its complications, including early mortality from cardiovascular causes."
Other experts agree that Americans should cut back on their consumption of added sugar in processed foods to improve health.
Last year, in another literature review published in Open Heart, Dr DiNicolantonio concluded that consuming added sugar in the diet contributes to hypertension (Open Heart. 2014;1:e000167), so guidelines should shift focus from salt to sugar.
What is less clear is whether the fructose component of added sugar is driving type 2 diabetes, as Dr DiNicolantonio and colleagues now report.
Does Added Sugar Affect Diabetes Prevalence?
About three-quarters of all packaged foods and beverages in the US contain added sugar, and it is estimated that Americans eat up to 22 to 47 teaspoons of sugar a day, including hidden sugar in processed foods, Dr DiNicolantonio said.
But there is often confusion about what added "sugar" really is and how it is metabolized in the body. Sugar (or sucrose), which comes from cane sugar or beets, is composed of 50% glucose and 50% fructose.
High-fructose corn syrup, which is derived from corn and is typically used in sugar-sweetened beverages, also contains glucose and fructose in similar amounts. However, in sucrose, but not in high-fructose corn syrup, the glucose and fructose are linked by chemical bonds, although these are rapidly broken down by stomach acid and gut enzymes once eaten.
As Dr Marion Nestle, a professor of nutrition, food studies, and public health at New York University, told Medscape Medical News: "Pity the poor public. It takes a degree in carbohydrate biochemistry to sort all this out."
Both sucrose and high-fructose corn syrup affect insulin similarly, "but whether they are exactly equivalent is under debate," she added. "Some evidence suggests that [high-fructose corn syrup], which is supposed to be 45% glucose and 55% fructose, actually has more fructose than that. Fructose metabolism is different from glucose metabolism. Some people think the differences matter a lot, others don't. The point is that both sucrose and [high-fructose corn syrup] contain both glucose and fructose and can be considered metabolically equivalent, for the most part."
In the current review, Dr DiNicolantonio and colleagues examined added sugar and type 2 diabetes.
They report that in one study, the risk for diabetes was 11-fold higher for each 150-kcal per person per day increase in sugar vs a similar increase in total calories (PLoS One. 2013;8:e57873).
Another suggested that a diet with 5% rather than 18% or 33% sucrose may normalize fasting insulin levels (Am J Clin Nutr. 1981;34:2477-2483; Am J Clin Nutr. 2009;89:438-440; JAMA. 2004;292:927-934; Nutrients. 2014;6:2088-2103; Am J Public Health. 2013;103:2071-2077).
Another study found that participants who received isolated fructose had a 25% decrease in insulin sensitivity compared with participants who received isolated glucose (Am J Clin Nutr. 1980;33:273-278).
The net result of excess consumption of added fructose is derangement of both overall metabolism and global insulin resistance, say Dr DiNicolantonio and colleagues.
"The totality of the evidence is compelling to suggest that added sugar and especially added fructose (usually in the form of [high-fructose corn syrup] and table sugar), are a serious and growing public-health problem," they note.
Thus, the take-away message is "to switch from processed foods to whole foods," which could potentially lead to lower rates of diabetes-related morbidity and premature mortality, Dr DiNicolantonio said.
Most Experts Agree on Need to Reduce Added Sugar Intake
Asked to comment by Medscape Medical News, Dr Rachel Johnson (University of Vermont, Burlington), 2014–2016 past chair of the American Heart Association (AHA) Nutrition Committee, agreed that "high intakes of added sugars, especially in the form of sugar-sweetened beverages, are associated with an increased risk of type 2 diabetes."
However, at the same time, "people should not be concerned about limiting fructose found in whole foods such as fruits and vegetables," she noted.
The AHA recommends limiting added sugars to no more than 6 tsp (24 g), or 100 calories, per day for women, and 9 tsp (36 g), or 150 calories, per day, for men and cutting sugar-sweetened beverage consumption to no more than 36 ounces, or 450 calories, per week.
"This is good, actionable advice for clinicians and patients," she said.
Dr Nestle added that "sugars of any type add calories and are devoid of nutrients, but small amounts add 'deliciousness' to foods and are unlikely to be harmful if the rest of the diet is reasonably healthy and balanced in calories."
However, practically everyone would be healthier eating less added sugar of any type, she agreed.
Guidelines recommend that added sugars should be no more than 10% of calories; that is, a person who typically eats 2000 calories per day should consume no more than 200 calories, or 12 tsp (50 g), of added sugar—the amount in one 16-ounce soda, Dr Nestle explained. But most people are consuming twice as much.
She reiterated that most fructose is consumed along with equal amounts of glucose, so it's hard to distinguish the effects of one from the other, she pointed out. But "while waiting for researchers to sort all this out, cutting down on sugars is a really good idea."
Meanwhile, David Knowles, spokesperson for the Corn Refiners Association (Washington, DC), takes issue with the review's distinction between fructose and sugar.
"Calories from added fructose at normal consumption levels do not pose a unique risk for diabetes," he asserted in an email to Medscape Medical News.
And like Dr Nestle, he noted that "fructose…is typically consumed in combination with glucose." In addition, the researchers' claim comes largely from in vitro and animal studies and human trials where people consumed unrealistic amounts of pure fructose, he said.
A spokesperson from the nutrition committee of the American Diabetes Association (ADA) told Medscape Medical News that the organization's guidelines, like others, recommend that people should minimize their intake of added sugar in foods and limit or avoid intake of sugar-sweetened beverages.
Moreover, "with the proposed changes to the food label to include the grams of added sugars, Americans will be able to make more informed decisions on food and beverage choices to minimize added sugars."
The authors report no relevant financial relationships. Dr Nestle reports she has no relevant financial relationships.
Mayo Clin Proc. 2015. Published online January 29, 2015. Abstract
Medscape Medical News © 2015 WebMD, LLC
Send comments and news tips to firstname.lastname@example.org.
Cite this: Added Sweeteners in Processed Foods Tied to Diabetes - Medscape - Jan 29, 2015.