Seminal fluid can have wide-ranging effects on reproductive fitness – from affecting sperm fertilisation capacity and female reproductive physiology, to influencing offspring viability and health. Seminal fluid can also change in response to environmental conditions including diet, which of itself is known to affect reproductive traits and fitness outcomes. However, an understanding of how paternal diet alters seminal fluid composition and how these effects relate to foetal development remains elusive. Here, we applied the Geometric Framework for Nutrition to systematically manipulate dietary macronutrient balance in male mice and determine dietary effects on the seminal vesicle fluid (SVF) proteome and related differences to aspects of foetal development in offspring sired by these males. We 1) identify and determine the largest number of proteins in the mouse SVF proteome to date, 2) identify a set of proteins that are significantly affected by dietary macronutrient balance, 3) show that differences in a protein related to lipid mobilisation and metabolism (APOA4) are correlated with foetal development, and 4) detect dietary effects on aspects of foetal development that were unrelated to SVF protein abundance. This study provides a comprehensive characterisation of the male SVF proteome across nutritional space and highlights potential functional ways in which male diet and the seminal fluid may mediate fitness.