Poor development in utero may favor the development of obesity in adulthood. Animal studies showed that embryo manipulation in vitro or nutritional insults during the embryonic and fetal stages of development may lead to obesity in adult life. We studied the in vitro proliferation and differentiation of adipocytes to investigate whether early protein restriction may program cell growth and development. In a series of experiments, 2 different low-protein diet protocols were compared. In both cases, pregnant rats were fed a diet with a high (18-20%) or low (8-9%) protein content during gestation and/or lactation. Preadipocytes were isolated from the fetuses, neonates, and weanling offspring. Moderate protein restriction, imposed during either gestation and/or lactation, did not affect the capacity of preadipose cells to divide or store fat. Because previous studies showed that early protein restriction alters the metabolism of sulfur amino acids, we also investigated the effects of methionine, taurine, and homocysteine on proliferation and differentiation of preadipocytes. The supplementation of the diet with methionine or the addition of homocysteine and taurine to the culture media did not influence the development of preadipocytes. We obtained no evidence for the direct reprogramming of the precursor or stem cells and suggest that the subsequent alteration in fat accretion may therefore reflect a change in the neuroendocrine environment.