Dietary factors in the aetiology of diabetes

Quite different nutrition-related environmental factors influence the development of type 1 insulin-dependent diabetes (IDDM) and type 2 non-insulin-dependent diabetes (NIDDM). IDDM is characterized by progressive beta-cell destruction which leads to complete insulin deficiency; at the time of diagnosis 80-90% of beta cells have been destroyed. In children there is epidemiological evidence that high intake of nitrites and N-nitroso compounds, early introduction of cow's milk to the diet and short duration or absence of breastfeeding increase the risk of IDDM. Studies in experimental animals suggest that cow's milk and soy proteins may be diabetogenic. There is current interest in the effects of free radical scavengers, particularly niacin and natural and synthetic antioxidants on the incidence of IDDM. These findings from ecological, animal, and human case-control studies remain to be evaluated in prospective cohort studies covering infancy and childhood and finally in human intervention trials. NIDDM is characterized by insulin resistance which is complicated by impaired insulin secretion at the time of appearance of hyperglycaemia and clinical diabetes. Its preclinical development is insidious and poorly defined, and there is little direct evidence that the same factors which influence metabolic control in clinical diabetes also affect the preclinical development of the disorder. Obesity, particularly of the abdominal type, is common in people who develop NIDDM, and weight control by appropriate diet and physical activity is probably the most important measure for preventing NIDDM. High (saturated) fat intake seems to be associated with insulin resistance, obesity and increased risk of NIDDM, and diets high in carbohydrate seem to protect from glucose intolerance and diabetes, mainly owing to their high fibre content.