Increased dietary consumption of sugar has been implicated in a number of clinical pathologies, including obesity and other metabolic diseases. High fructose corn syrup, a sugar mixture of about 40% glucose and 60% fructose, is a ubiquitous sweetening additive in a number of drinks and food. In this study, we have investigated the metabolism of these two types of sugar in SfXL glioblastoma and HuH7 hepatocarcinoma cell lines. 13C NMR spectroscopy was used in this study due to high specificity courtesy of the wide chemical shift dispersion of carbon-13. The goal of this study was to investigate the metabolism of fructose and glucose in brain and liver cancer, given the ubiquity of these two sugars in Western diet and the high sugar addiction of these cancers. The main finding of this preliminary work is that, despite the same caloric content of these two sugars, fructose and glucose metabolized quite differently in brain and liver cancer cells. In the absence of glucose in the media, there was no indication of metabolism of [U-13C6]fructose in SfXL cells. In the presence of unlabeled glucose in DMEM, we have observed metabolism of [1-13C]fructose into [3-13C]lactate. However, lactic acid production rate from [1-13C]fructose is found to relatively slower compared to lactic acid production from [U-13C6]glucose. On the other hand, substantial lactic acid production from [U-13C6]fructose was observed in HuH7 liver cancer cells due to the presence of specialized hepatic enzymes that can metabolize fructose. Metabolic kinetics of these two sugars as well as the NMR results of co-administered 13C-fructose and 13C-glucose will be presented.