The invention is based on a correlation observed between visceral fat and gut flora. The invention relates to a product increasing the relative proportion of bifidobacteria in the intestines and to be used for preventing formation of visceral fat or for reducing the amount thereof in the body. In particular, the product increases the ratio of bifidobacteria to Clostridia. The invention also relates to determining visceral fat in the body by determining the relative proportion of bifidobacteria or Clostridia or their ratio to each other in the intestines. The invention further relates to a method for estimating, in the same manner, the health risk associated with obesity.
