Effect of citrus fruit and juice consumption on risk of developing type 2 diabetes: Evidence on polyphenols from epidemiological and intervention studies

Citrus fruits are commonly consumed worldwide in both fresh and processed forms, especially as juices. While fruit consumption is perceived as beneficial for long-term health, the effects of fruit juices are more controversial, linked to high intrinsic sugar content. On the other hand, citrus juices, like the fruits, are rich in many nutrients including vitamin C, and also contain various bioactive components such as (poly)phenols. This review examines the effect of citrus fruits, juices and constituent (poly)phenols on the risk of type 2 diabetes through a critical evaluation of the literature, considering data from epidemiological and human intervention studies, both acutely and chronically. Epidemiological studies show some protection from consuming citrus fruits against developing type 2 diabetes, but the outcomes for citrus juices are conflicting. The direct acute effect of citrus (poly)phenols on postprandial glycaemic response, a risk factor for type 2 diabetes, is relatively small. Improved fasting glucose, fasting insulin and insulin resistance were observed after longer periods of citrus juice consumption. High inter-individual variation in flavanone bioavailability is possibly one of the main factors affecting the physiological responses in humans, as well as changes in gut microbiota. To further understand the effect of citrus consumption on type 2 diabetes risk and to shed light on the interconnection between the gut microbiome, bioavailability and bioefficacy, future acute and chronic studies linking these factors with clinical outcomes are recommended. •Citrus fruits are rich in bioactive (poly)phenolic flavonoids and vitamin C.•Longer-term citrus consumption favourably modulates the markers of type 2 diabetes.•Data from epidemiological studies are mostly inconclusive.•Direct acute effect of citrus on postprandial glycaemic response is relatively small.•Clinical response depends on gut microbiota and flavanone bioavailability.