amino acids may also have critical roles. Rats fed an isocaloric low protein diet have offspring whose pancreatic islet cells have impaired insulin release. However, supplementation of the maternal low protein diet with taurine alone restored the insulin secretion of the fetal islets. 84 It seems likely that other specific amino acids are important in particular phases of organ development in different tissues, but this has not yet been explored in detail. Glycine, for example, appears to be a conditionally essential amino acid for a number of important metabolic compounds including nucleic acids, collagen, haeme and keratin. 85 Marginal glycine insufficiency appears to be common even in pregnant women with otherwise adequate diets, so that in some pregnancies the ability of the mother to provide glycine for herself and the developing fetus is marginal or inadequate. 86 This marginal insufficiency can be exacerbated if the dietary methionine content is increased, apparently because glycine is consumed in detoxification of the excess of methionine. 87 From these examples it is possible to see that the balance of protein and carbohydrate in the diet, and the balance of different amino acids, can have critical effects on fetal growth and thus may be important nutritional programming influences which have yet to be explored in detail. Fluctuations in nutrient supply to the fetus may also have important effects on fetal growth and the programming of later disease risk. Maternal diabetes in pregnancy is a relatively common cause of altered fetal nutrient supply, with increased glucose