Fried Foods, Gut Microbiota, and Glucose Metabolism

Hot oil–based frying is a popular cooking method that makes food more appealing in texture and aromatic, thus improving palatability. Fried foods are considered unhealthy because frying may increase the energy density of foods and therefore energy intakes as well as deteriorate oils through the process of oxidation and hydrogenation, leading to a loss of unsaturated fatty acids such as linoleic and linolenic acids but increase in trans fatty acids, oil degradation, and advanced glycation end products (1,2). In epidemiological studies, high intakes of fried foods have been associated with a variety of adverse health outcomes including type 2 diabetes (T2D), although the results are not entirely consistent (3–6). The conflicting findings are partly due to the diverse types of oil used in frying foods. For instance, null associations between fried foods and T2D risk were reported in populations with fried foods prepared using mainly olive oil, which is more resistant to oxidation than other common oils used for frying such as corn oil (4). In addition, the varying compositions of the foods being fried and frying conditions (temperature, duration) may also trigger the heterogeneous results. An extra layer of complexity in the inconsistent observations is introduced by various confounding factors such as weight gain, high blood pressure, and lipidemia, which are correlated with both fried food consumption and T2D risk (1,7). The causality of fried foods in glucose dysregulation and the development of T2D could only be detected in investigations in which the cofounding was rigorously controlled, such as randomized clinical trials. In addition, the potential mechanisms underlying the observed adverse associations between fried foods …