A complex combination of adult health-related disorders can originate from developmental events that occur in utero. The periconceptional period may also be programmable. We report on the effects of restricting the supply of specific B vitamins (i.e., B12 and folate) and methionine, within normal physiological ranges, from the periconceptional diet of mature female sheep. We hypothesized this would lead to epigenetic modifications to DNA methylation in the preovulatory oocyte and/or preimplantation embryo, with long-term health implications for offspring. DNA methylation is a key epigenetic contributor to maintenance of gene silencing that relies on a dietary supply of methyl groups. We observed no effects on pregnancy establishment or birth weight, but this modest early dietary intervention led to adult offspring that were both heavier and fatter, elicited altered immune responses to antigenic challenge, were insulin-resistant, and had elevated blood pressure-effects that were most obvious in males. The altered methylation status of 4% of 1,400 CpG islands examined by restriction landmark genome scanning in the fetal liver revealed compelling evidence of a widespread epigenetic mechanism associated with this nutritionally programmed effect. Intriguingly, more than half of the affected loci were specific to males. The data provide the first evidence that clinically relevant reductions in specific dietary inputs to the methionine/folate cycles during the periconceptional period can lead to widespread epigenetic alterations to DNA methylation in offspring, and modify adult healthrelated phenotypes. E vidence from both epidemiological studies in humans and direct intervention studies in animals indicates that altering key developmental processes in utero can predispose offspring to many late-onset diseases such as dyslipidemia, type II diabetes, and heart disease (1, 2). In this regard, the effects of gross nutrient or protein deficiencies in maternal diet during pregnancy are well documented (3), although little is known about the effects of specific nutrients or the timing and mechanistic basis of nutrient programming (4). Here we investigated the effects of restricting the supply of specific B group vitamins (i.e., vitamin B 12 and folate) and sulfur amino acids (in particular, methionine) from the diet of adult female sheep from 8 weeks preceding until 6 days after conception, within physiological ranges encountered in both sheep (5) and humans (i.e., within the 5th and 95th percentiles) (6, 7). These micronutrients are important intermediates and/or have specific regulatory functions in the linked methionine-folate cycles (5, 7). In rodents, maternal supraphysiological methyl group supply and a low-protein diet (50% control) offered throughout pregnancy altered DNA methylation of candidate genes (agouti, glucocorticoid receptor, and peroxisomal proliferator-activated receptor-␣) (8, 9), but the extent of methylation change in these or more clinically relevant diets is not known. Gametes and preimplantation emb...