Variations in nutritional intake during pregnancy have measurable effects on the circulating levels of maternal nutrients, maternal weight gain, and birth weight of the offspring. A growing body of evidence indicates that alterations in maternal metabolism can also have long-term consequences in the offspring in relation to adult adiposity, glucose tolerance, and perhaps intellectual development. Therefore, recommendations for diet during pregnancy must be made with great care, and with as much scientific understanding as possible. Nutritional advice traditionally given to all pregnant women, including those with gestational diabetes mellitus (GDM) or noninsulin-dependent diabetes, does not allow for individual differences in caloric needs as a function of the degree of maternal obesity and thus, may encourage excessive weight gain. Evidence reviewed below suggests that adjusting caloric intake to meet new guidelines for weight gain during pregnancy may be advantageous in reducing maternal blood sugar and insulin levels, without producing abnormalities in other metabolic variables. Modest caloric reduction which limits excessive weight gain in the mother may also be associated with a small reduction of fetal weight. However, more stringent dietary manipulations in obese gravida should be discouraged as a routine measure until more knowledge is available from large-scale clinical trials about their effects on the entire panoply of maternal nutrients and their impact on the offspring.