Could fructose be the cause of your weight gain?

What do you think is listed as the second ingredient in a can of Coke-a-Cola?  As many of you probably already know or can guess, it is high-fructose corn syrup. Of all the ingredients, why is high-fructose corn syrup important? A few years ago, someone in my family loved Coke-a-Cola, and drank numerous cans a week. When that family member chose to live a healthier lifestyle, she decided to cut soda out of her diet. As a result, she lost ten pounds! Now, how can something this simple show such significant results?

  Fructose has the same molecular weight and chemical formula as glucose, but is chemically distinct (3). As we have learned in class, high blood glucose levels trigger insulin release from the beta cells in the pancreas, inducing glucose uptake via the glucose transporter GLUT4. The glucose can then undergo glycolysis or it can be stored as glycogen. However, a recent study by Lanaspa et al. found that glucose metabolism can also generate fructose in mice, resulting in negative consequences (1).

Lanaspa et al. fed wild type and knockout mice a diet of 10% glucose/regular food for 14 weeks (l). The knockout mice could not convert glucose to fructose or degrade fructose within the liver. As a result of this diet, the wild type mice had increased body weight, obesity, and insulin levels, and a fatty liver due to increased energy absorption. These symptoms suggested metabolic syndrome. Contrastingly, the knockout mice did not produce any symptoms. The researchers explain that high glucose levels in the wild type mice triggered induction of the polyol pathway, converting glucose to sorbitol, which was then converted to fructose, resulting in higher fructose and sorbitol levels within the wild type mice livers. The knockout mice were protected form this pathway, and therefore did not show metabolic syndrome symptoms (1). These findings are important, because they suggest that fructose, having a low glycemic index, does contribute to the problem of metabolic syndrome.

While these findings were shown within mice models, Lanaspa et al. suggest that this study could provide context for human subjects, since excess sugary soft drink consumption results in similar symptoms: increased visceral and hepatic fat and triglycerides (1). Further studies also found that a low- or moderate-fructose diet in humans increased weight loss and reduced blood pressure (2). These studies highlight fructose’s importance in metabolic syndrome through increased weight gain and fat storage. So, next time you reach for a sugary drink, look out for fructose!

References:

1. Lanaspa MA, Ishimoto T, Li N, Cicerchi C, Orlicky DJ, Ruzicky P, Rivard C, Inaba S, Roncal-Jimenez CA, Bales ES, Diggle CP, Asipu A, Petrash JM, Kosugi T, Maruyama S, Sanchez-Lozada LG, McManaman JL, Bonthron DT, Sautin YY, Johnson RJ. Endogenous fructose production and metabolism in the liver contributes to the development of metabolic syndrome. Nature Communications 4: 2434, 2013.

2. Madero M, Arriaga JC, Jalal D, Rivard C, McFann K, Perez-Mendez O, Vazquez A, Ruiz A, Lanaspa MA, Jimenez CR, Johnson RJ, Lozada LGS. The effect of two energy-restricted diets, a low-fructose diet versus a moderate natural fructose diet, on weight loss and metabolic syndrome parameters: a randomized controlled trial. Metabolism Clinical and Experimental 60: 1551-1559, 2011.

3. Samuel VT. Fructose induced lipogenesis: from sugar to fat to insulin resistance. Trends in Endocrinology and Metabolism 22(2): 60-65, 2011.