AbstractObjective:The insulin-like growth factor (IGF) system has been implicated in the aetiopathogenesis of cancer, cardiovascular disease and diabetes. Since dietary factors and ethnicity are considered contributory to the development of these diseases, we examined the IGF system in relation to nutritional intake by ethnic group.Design, subjects and setting:Dietary intake in 257 subjects of White European, African-Caribbean and Pakistani ethnic origin living in Manchester, UK was assessed using ethnic-group-specific food-frequency questionnaires to assess habitual nutrient intake over the previous 12 months. Fasting IGF-I, IGF-II and IGF-binding protein-1 (IGFBP-1) concentrations were determined and their relationship to specific dietary constituents was analysed.Results:Analysis by quintiles of nutrient intake showed a significant increase in circulating IGF-I concentration with increasing dietary fat intake (F for trend = 3.9, P < 0.01), saturated fat intake (F = 3.3, P = 0.01) and for protein intake (F = 4.2, P < 0.01). There was also a significant increase in IGF-II by quintiles of dietary protein intake (F = 2.7, P < 0.05). There was a trend for increasing IGF-I with increasing energy intake. The relationships between circulating concentration of IGFBP-1, an acute regulator of IGF action, and fat/protein intake were opposite to those for IGF-I and IGF-II. Multiple linear regression modelling showed that people of Pakistani origin and older subjects had lower levels of IGF-I (Pakistani origin vs. others, P < 0.001) (age, P < 0.001 for both). There was an independent inverse relationship between IGF-I and dietary carbohydrate intake (P = 0.036).Conclusions:This study provides evidence for a dietary contribution to regulation of the IGF system, although the effects of ethnicity on circulating IGF levels remain dominant. We propose that the IGF system's influences on cancer risk in specific ethnic groups are potentially modifiable by dietary intervention.