Recent observational studies suggest that mean birth weight and body fat growth in the first year of life have increased continuously over the last decades. Both elevated birth weight and early fat mass are potential risk factors for childhood obesity. Experimental and limited clinical data suggest that the dietary ratio of n-6 to n-3 fatty acids (FAs) during pregnancy is critical for early adipose tissue growth. The aim of this randomized controlled study is to examine the effect of the supplementation with n-3 long-chain polyunsaturated FAs and reduction in the n-6/n-3 ratio in the diet of pregnant women/breast-feeding mothers on adipose tissue growth in their newborns using various methods for the assessment of body fat mass. Measurement of skinfold thickness in the newborn is the primary outcome parameter. Two hundred and four pregnant women will be recruited before the 15th week of gestation and randomly assigned to either active intervention or an isocaloric control diet. This upcoming study will explore the potential of this dietary approach to limit early adipose tissue growth and may contribute to the development of a new strategy for the primary prevention of childhood obesity.