The Collaborative International Dictionary of English v.0.48:

Macrobiotics \Mac`ro*bi*ot"ics\, n.
   1. (Physiol.) The art of prolonging life.
      [1913 Webster]

   2. Specifically: A philosophy or attitude that health and
      long life are promoted by adhering to a diet consisting
      mostly of whole grains, with some vegetables, beans,
      fruit, and moderate amounts of seafood. However, the
      absence of essential nutrients such as fat makes such a
      diet of questionable value if strictly adhered to.
      [PJC] macrocephalic

WordNet (r) 3.0 (2006):

macrobiotics
    n 1: the theory of promoting health and longevity by means of
         diet (especially whole beans and grains)