The composition of the human body can be looked at from the point of view of either mass composition or atomic composition. To illustrate both views, the adult male human body is approximately 57% water, and water is 11% hydrogen by mass but 67% by count of atoms (i.e. 67 atomic percent). Thus, most of the mass of the human body is oxygen, but most of the atoms in the human body are hydrogen atoms. Both mass-composition and atomic composition figures are given below (see pie graphs and table).
Body composition may also be analyzed in terms of molecular type (e.g., water, protein, connective tissue, fats (or lipids) Hydroxylapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, muscle, bone, etc. In terms of cell type, the body contains hundreds of different types of cells, but notably, the largest number of cells contained in a human body (though not the largest mass of cells) are not human cells, but consist of bacteria (bacterial cells) residing in the normal human gastrointestinal tract.
