Soft Drinks Cause Metabolic Syndrome: But What About Fruit Juice?

Evidence suggests that the increasing consumption of soft drinks is a major cause of the obesity epidemic in Western nations. Sugar sweetened soft drink are detrimental to health because they oversupply the liver with fructose, which has been shown in animal and human experiments to cause non-alcoholic fatty liver disease, insulin resistance and metabolic syndrome. High fructose consumption may be the cause of the abdominal obesity that accompanies metabolic syndrome, something that increases the risk of mortality significantly. Fructose may cause abdominal obesity because unlike glucose it can only be processed by the liver. Small quantities can be converted to liver glycogen, but high intakes overburden the liver and result in fatty acid production, some of which are stored in the liver and skeletal muscle. It is these accumulated fatty acids in the liver and skeletal muscle that cause the insulin resistance characteristic of metabolic syndrome.

Soft drinks are artificially sweetened in Europe and the United States by sucrose or high fructose corn syrup. However, fruit juice contains natural sucrose and so can be a source of fructose. Researchers are therefore interested in the comparative metabolic effects of the fructose in artificially sweetened soft drinks and fruit juices. Using a meta-analysis design study, researchers1 have investigated the effects of homemade fruit juice, commercially available fruit juice, instant fruit drink (squash) and a regular sucrose sweetened soft drink on the risk of metabolic syndrome in Costa Rican subjects. Consumption of the commercially available instant fruit drink and sucrose sweetened soft drink were significantly associated with waist circumference and fasting triglyceride levels [as represented by the very low density lipoprotein (VLDL) subfraction]. However, increasing intakes of homemade fruit juices were associated with increasing high density lipoprotein.

Therefore commercially available soft drinks sweetened artificially with sucrose are associated with detrimental lipid changes and increase abdominal obesity (as measured by waist circumference). In contrast homemade fruit juices are associated with relative benign blood lipid changes. The researchers calculated that consuming one or more sucrose sweetened soft drink or instant fruit drink per day was associated with a significantly increase prevalence ratio (1.42) compared to the absence of consumption. Substituting one serving of instant fruit drink with one serving of homemade fruit juice was associated with a 29 % reduction in odds ratio of metabolic syndrome and substituting one serving of regular soda with one serving of homemade fruit juice was associated with a 30 % reduction in odds ratio of metabolic syndrome. Consumption of the commercially available fruit drink was associated with lower blood glucose levels but this was not significant following adjustment.

The authors reported that it was younger participants who consumed the most sucrose sweetened soft drinks. Sucrose sweetened soft drinks are marketed generally at the younger generation and it is not surprising that they had the highest intakes. That homemade fruit juice contains fructose but consumption is not associated with metabolic syndrome or detrimental lipid changes suggests that their might be a protective factor contained within the fruit. This may relate to the fibre, some of which may appears in the drinks as particulate matter. In addition, fruit contains relatively low levels of fructose and so may not overload the liver to the same extent as sucrose sweetened soft drinks. Finally, fruit contains polyphenols, which may function as antioxidants in humans. These antioxidants can protect the liver because they may provide reducing power to peroxisomes which prevents cellular damage to liver cells, and may allow oxidation of fatty acids.

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1Mattei, J., Malik, V., Hu, F. B. and Campos, H. 2012. Substituting homemade fruit juice for sugar-sweetened beverages is associated with lower odds ratio of metabolic syndrome amongst Hispanic adults. Journal of Nutrition. 142: 1081-1087

About Robert Barrington

Robert Barrington is a writer, nutritionist, lecturer and philosopher.
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