US Guidelines for Consumption of Sugar May Be Too High

Steven Fox and Jacqueline A. Hart, MD

July 29, 2011

July 29, 2011 — Results from a new study show that adults who consumed 25% of their daily calories as fructose or high-fructose corn syrup beverages (a percentage within current government guidelines) for 2 weeks experienced increases in serum levels of cholesterol and triglycerides.

The authors of the study, recently accepted for publication in the Endocrine Society’s Journal of Clinical Endocrinology & Metabolism and slated to be published in the October 2011 print issue, say the results should spur the government to reevaluate the guidelines.

Senior author Kimber Stanhope, PhD, from the departments of nutrition and molecular biosciences, University of California, Davis, and colleagues say the study was conducted to help sort out a discrepancy in 2 prominent sets of recommendations: The Dietary Guidelines for Americans, jointly published by the US Department of Health and Human Services and the US Department of Agriculture, recommend that people consume a maximum of 25% of their daily calories as added sugars. In contrast, the American Heart Association recommends an upper limit of 5%.

"While there is evidence that people who consume sugar are more likely to have heart disease or diabetes, it is controversial as to whether high sugar diets may actually promote these diseases, and dietary guidelines are conflicting," remarked Dr. Stanhope in a press release.

To shed light on the effects of the higher government-recommended threshold, the researchers had 48 overweight and normal-weight adults (age, 18-40 years; body mass index, 18-35 kg/m2) consume beverages that contained fructose, high-fructose corn syrup, or glucose at the 25% upper limit for calorie intake for 2 weeks.

During the first 3.5 days of the trial, the participants stayed at an inpatient facility for baseline testing while consuming a balanced diet consisting of 55% complex carbohydrates. The following 12 days were at home on an ad libitum diet with the addition of 3 daily drinks of glucose-, fructose-, or high-fructose corn syrup-sweetened beverages (n = 16/group) that provided 25% of their energy requirements. The last 3.5 days were spent back at the inpatient facility for repeated testing while the participants were consuming energy-balanced diets containing 25% sugar-sweetened beverages and 30% complex carbohydrate.

At the end of the study period, participants who consumed fructose or high-fructose corn syrup in their drinks exhibited elevated blood levels of low-density lipoprotein (LDL) cholesterol, triglycerides, and apolipoprotein B (apo B).

Participants who consumed glucose in their beverages exhibited no such changes. More specifically, the 24-hour triglyceride area under the curve (AUC) increased compared with baseline during consumption of fructose (increase, 4.7 ± 1.2 mmol/L x 24 hours; P = .0032) and high-fructose corn syrup (increase, 1.8 ± 1.4 mmol/L x 24 hours; P = .035), but not glucose (decrease, 1.9 ± 0.9 mmol/L x 24 hours; P = .14). Similarly, fasting LDL and apoB concentrations were increased during consumption of fructose (LDL increase, 0.29 ± 0.082 mmol/L; P = .0023; apoB increase, 0.093 ± 0.022 g/L; P = .0005) and high-fructose corn syrup (LDL increase, 0.42 ± 0.11 mmol/L; P < .0001; apoB, 0.12 ± 0.031 g/L; P < .0001), but not glucose (LDL increase, 0.012 ± 0.071 mmol/L, P = .86; apoB increase, 0.0097 ± 0.019 g/L; P = .91).

One limitation is the lack of inclusion of sucrose in the study.

"There is growing evidence linking increases of postprandial triglyceride concentrations with proatherogenic conditions," Dr. Stanhope and her colleagues explain. Their results add to this existing evidence, even in young adults. "It is [also] important to note," write the authors, "that for both the current and [a] previous study [by our research group], the differential effects of fructose and [high-fructose corn syrup] compared to complex carbohydrate on the 24-h [triglyceride] profile were most marked in the late evening, approximately 4 and 6 hours after dinner. Studies investigating the relationship between this late-evening peak and proatherogenic changes would be of interest, as would investigations into the sources of the [triglycerides] that contributes to these peaks," such as diet or fatty acids derived from adipose lipolysis.

According to the researchers, survey data suggest that 13% of the US population consumes 25% or more of their calories from added sugar. The current data provide evidence that this level of sugar consumption in young, healthy, normal, and overweight adults contributes to dyslipidemia after only 2 weeks and contradicts conclusions from recent reviews suggesting that "sugar intakes as high as 25-50% of energy have no adverse long-term effects" in terms of the metabolic syndrome, and "that fructose consumption up to 140 grams/day does not result in a biologically relevant increase of fasting or postprandial [triglycerides] in healthy, normal weight or overweight or obese" individuals.

Furthermore, the researchers conclude, their findings indicate the need for the government to reconsider its recommendations that include a maximal upper limit of 25% of total energy requirements from added sugar.

The study was supported by the National Heart, Lung and Blood Institute and by the National Center for Research Resources, both of the National Institutes of Health. One author has consulted for Denka Seiken Company and for Otsuka Pharmaceutical Company, Ltd, both in Tokyo, Japan. Another author is currently employed by Denka Seiken Co., and a third was formerly employed by this same company. Dr. Stanhope and the remaining 8 authors have disclosed no relevant financial relationships.

J Clin Endocrinol Metab. Expected print publication October 2011.


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