Formerly dietary standards took no account of the ash constituents because it was assumed that dietaries furnishing sufficient energy and protein would always be adequate as regards the "inorganic" elements. As explained in previous chapters this assumption is not safe in the case of calcium, phosphorus, or iron. In the light of present knowledge adequate dietary standards must provide for these elements. The experimental evidence regarding the minimum requirements of the body for each of these elements has been reviewed in earlier chapters and there has been but brief discussion of the relation between minimum and optimum amounts.

The evidence thus far available indicates an average minimum requirement for equilibrium, per man per day, of 0.45 gram calcium (0.63 gram CaO), 0.96 gram phosphorus (2.20 grams P2O5), and about 0.010 gram (10 milligrams) of iron.

To allow only these quantities in the daily food would correspond to an allowance of only 50 grams per man per day of protein.

If the standard allowance be set 50 per cent above the indicated average minimum corresponding to an allowance of 75 grams of protein we obtain Calcium, 0.68 gram (equivalent to 0.95 gram of calcium oxide, CaO). Phosphorus, 1.44 grams (equivalent to 3.30 grams of P2O5). Iron, 0.015 gram (15 milligrams).

If these be taken as proper allowances per man of 70 kilograms whose energy requirement averages 3000 Calories per day, then the corresponding allowances for other adults or for families containing children could also be stated as follows:

If it be desired to provide as liberal a margin of safety here as in the case of a protein allowance of 100 grams per man per day, then the above figures must obviously be increased by one third.