Dietary fat type influences total milk fat content in lean women.

Trans fatty acids (TFA) are found naturally in some foods (e.g., dairy products) as well as many processed foods made with partially hydrogenated vegetable oils (PHVO). Data from a growing literature suggest that some TFA decrease milk fat in lactating animals. Because the physiologic effects of TFA in lactating women are unknown, this study was designed to investigate the effects of TFA consumption on human milk fat. A randomized, crossover design (n = 12) was used to study the effect of 3 dietary treatments: high PHVO (regular margarine), low PHVO (low TFA margarine), or low PHVO but high in naturally occurring TFA (butter) on milk fat. Treatments were administered for 5 d, with 7-d washout periods. Maternal adiposity was estimated by dual-energy X-ray absorptiometry. Milk and blood were collected on d 5 of each intervention period. In general, milk and serum fatty acid concentrations mirrored those of the dietary treatments. There were significant interactions between treatment and maternal adiposity on milk fat and infant milk consumption, as well as on serum glucose and nonesterified fatty acid (NEFA) concentrations. Consumption of regular margarine, compared with low TFA margarine, resulted in lower milk fat in leaner, but not in more obese women. Consumption of either regular or low TFA margarine, compared with butter, elevated serum NEFA concentrations in the more obese women. In summary, consumption of regular margarine, compared with low TFA margarine, decreased milk fat in lean women. Further studies are required to determine whether infant milk consumption might compensate for this potentially important change in milk composition.