A new study which claims that fructose may play a unique role in the development of obesity and diabetes is limited by several study flaws, including contradicting research, exaggerated consumption levels, small sample size and reliance on animal research.
In the 21-person study “Fructose ingestion acutely stimulates circulating FGF21 levels in humans”, research subjects — some healthy and some with metabolic syndrome — participated in three trials in which they consumed one of three beverages made up of either fructose, glucose or a combination. After consumption, blood samples were taken with researchers looking for impact on the fibroblast growth factor 21 (FGF21), a recently discovered hormone produced in the liver and in fat tissue. Previous research has hypothesized that FGF21 may play a role in glucose and fat homeostasis in rodents and researchers in this study tested this hypothesis in humans. (More about thestudy located here.) Researchers concluded that FGF21 may be involved in fructose metabolism and that fructose may be associated with metabolic disorders such as diabetes.
However, the study suffered from several limitations that hamper the generalizability of the findings, including:
- The study sample only included 21 participants. The small sample size in this study makes it unlikely that results will be applicable to the majority of populations. Further, as noted by the researchers, there was significant variability between participants, which could also impact the generalizability of the findings.
- The hypothesis for the study was based on rodent research. The hypothesis from which this study was based came from results of research in rodents. Rodents have biologic and metabolic pathways that are different from humans.
- Fructose intake was more than typical for single consumption. Participants in the study consumed up to 75 grams of fructose at one time. In 2013, a study by Carden & Carr found that the average daily intake of fructose had declined since 1999 and was 62.4 grams in 2009 based on data from the U.S. Department of Agriculture (USDA). They further concluded that the rise in obesity rates in the U.S. was more likely due to an overall increase in daily caloric intake.
- The results are contradictory to recent research.Recent research by Kaverna et al. (2014) and reviews by Chiu et al. (2014) and Chung et al. (2014) found that fructose was not associated with risk of nonalcoholic fatty liver disease (NAFLD). Another small study conducted by Heden et al. (2014) found that high fructose intake was not associated with poor metabolic health in adolescents, the highest consumers of fructose. Finally, a recent review by van Buul et al. (2014) concluded that fructose is not associated with obesity, noting that there are a number of contributing factors.
- The findings are preliminary. As this is the first study conducted in humans to look at this biological process, additional research needs to be done in order to show whether or not there may be an association.