There is good clinical data to suggest that moderate consumption of wine can reduce the risk of diabetes. Animal studies are suggestive that the polyphenol in wine, resveratrol, may be helpful in preventing and treating some metabolic diseases, including diabetes.
Salas-Salvadó J review in 2011 "The role of diet in the prevention of type 2 diabetes" stated that "The conclusion is that there is no universal dietary strategy to prevent diabetes or delay its onset. Together with the maintenance of ideal body weight, the promotion of the so-called prudent diet (characterized by a higher intake of food groups that are generally recommended for health promotion, particularly plant-based foods, and a lower intake of red meat, meat products, sweets, high-fat dairy and refined grains) or a Mediterranean dietary pattern rich in olive oil, fruits and vegetables, including whole grains, pulses and nuts, low-fat dairy, and moderate alcohol consumption (mainly red wine) appears as the best strategy to decrease diabetes risk, especially if dietary recommendations take into account individual preferences, thus enabling long-time adherence."
In the 2011 review by Tomasz Szkudelski and Katarzyna Szkudelska "Anti-diabetic effects of resveratrol" (*Note that resveratrol is present in wine) they stated that "In the last few years, rodent studies and experiments in vitro provided evidence that resveratrol (3,5,4′-trihydroxystilbene)—a naturally occurring phytoalexin present in numerous plant species—exerts beneficial effects in the organism and may be helpful in preventing and treating some metabolic diseases, including diabetes. In general, the management of diabetes involves three main aspects: reduction of blood glucose, preservation of β cells, and, in the case of type 2 diabetes, improvement in insulin action. Data from the literature indicate that the beneficial effects of resveratrol in relation to diabetes comprise all these aspects".
In a 2014 review by Khemayanto H "Role of Mediterranean diet in prevention and management of type 2 diabetes" where the authors identified 451 articles with the key words: “Mediterranean diet” and “diabetes” up to 14 April 2014 the authors summarised:
"Daily moderate intake of alcohol (usually after a meal) in the form of red wine is one of the characteristic of Mediterranean diet. Moderate alcohol drinking is associated with 30% reduction of the risk of type 2 diabetes in both genders. The strongest inverse association was observed at 22–25 g/day. However, heavy consumption in both men and women (above 50 g/day for women and 60 g/day for men) were no longer provided protective effect but actually increased the risk for diabetes. Moderate alcohol consumption (40 g/day) for 17 days enhanced insulin sensitivity and plasma adiponectin levels, without any changes in the plasma tumor necrosis factor α (TNFα). Adiponectin stimulated glucose utilization and fatty acid oxidation. Adherence to the Mediterranean diet was associated with higher levels of adiponectin because of moderate consumption of red wine, which is inversely related to diabetes."
"Numerous studies on diabetic rats revealed the anti-hyperglycemic action of resveratrol. Among different beneficial effects of resveratrol found in diabetes, the ability of this compound to reduce hyperglycemia seems to be the best documented. The anti-hyperglycemic action of resveratrol was demonstrated in obese rodents and in two animal models of diabetes: in rats with streptozotocin- induced diabetes or with streptozotocin- nicotinamide-induced diabetes. Some studies also revealed that administration of resveratrol to diabetic rats resulted in diminished levels of glycosylated hemoglobin (HbA1C), which reflects the prolonged reduction of glycemia."
"The anti-hyperglycemic effect of resveratrol observed in diabetic animals is thought to result from its stimulatory action on intracellular glucose transport. Increased glucose uptake by different cells isolated from diabetic rats was found in the presence of resveratrol. Interestingly, in experiments on isolated cells, resveratrol was able to stimulate glucose uptake in the absence of insulin. The stimulation of glucose uptake induced by resveratrol seems to be due to increased action of glucose transporter in the plasma membrane. Studies on rats with experimentally induced diabetes demonstrated increased expression of the insulin-dependent glucose transporter, GLUT4, as a result of resveratrol ingestion, compared with diabetic animals not given resveratrol. It should be mentioned, however, that in some experiments on rats with streptozotocin-induced diabetes, resveratrol appeared to be ineffective and failed to decrease blood glucose."