Diet and the Blood Lipids

There is in general a fair agreement between workers as regards the lipid levels of the blood, but there are occasional groups of “normal” values for the lipids, both of whole blood and plasma, which are out of line, and even in a single series occasional widely discrepant values may be found. Inadequacy of methods, while undoubtedly responsible for some of the differences, does not account for all, and even with the improvement of methods, discrepancies continue to appear. Cholesterol has in general been found to be more frequently and widely variable than other lipid constituents of blood, partly because more attention has been given to it, but mainly because there seems no question that it does vary greatly. Thus in a recent paper (1) the total fatty acid values for normal human subjects were practically the same as those given by me 15 years ago, determined by a method entirely different in principle, while the cholesterol values were much lower although the method was essentially the same. Another example of an unexplained difference in lipid level may be noted in the phospholipid content of the plasma of the dogs used about 4 years ago for work on diabetes in this laboratory with that of the dogs used in the present work. Both groups were normal healthy dogs but the former had an average phospholipid content of 400 mg. per cent; the latter averaged 70 mg. per cent. Also, as may be seen from Table I, the phospholipid value for the plasma of the dog reported more than doubled in a few months. An investigation of the factors which affect the lipid content of the blood was desirable. It has been emphasized recently for other blood constituents (2) that the distribution of constituents between the corpuscles