432 



CELLS, TISSUES, AND ORGANISMS 



nomenon of aging, then we conclude that the process tends to proceed 

 at a fixed (logarithmic) rate but the general level is determined largely 

 by the cholesterol concentration. So the next step is to ask, what de- 

 termines the serum-cholesterol concentration? 



In part, this too is a function of age, as indicated by the rising 

 curves in Figure 4. But in Japanese men in the fifties the serum- 

 cholesterol level is far below the level of Minnesota men in the twen- 

 ties. The difference, we believe, is to be found in the diet. Though we 

 may argue about what precisely controls the development of athero- 

 sclerosis, there is no longer any doubt about the major importance of 

 the diet in the control of the serum-cholesterol level. 



Instead of talking about aging, it would be much easier to discuss 

 the influence of the various constituents of the diet on the serum- 

 cholesterol concentration. Many controlled experiments on man show 

 that the dietary fats are the dominant factor, and that the average 

 serum-cholesterol response of man to given changes in the amount and 

 kind of the fatty acids in the diet is predictable ( Keys, Anderson, and 

 Grande, 1959). On a constant diet, however, all men of the same age 

 do not have the same serum-cholesterol level. 



Some men are characterized by high levels, some by low, and 

 there is a strong tendency for individuals to maintain their relative 

 places in the distribution of cholesterol level in the population. Figure 

 8 shows our findings on the typical distribution of serum-cholesterol 

 values among physically healthy, middle-aged men controlled in a 

 closed institution on a rigidly constant diet and a fixed program of rest 

 and exercise. Repeated blood samples were drawn from each man, and 

 the means of the individual were used to compute the distribution, 

 which was then smoothed slightly to fit the normal curve. 



100 



Figure 7. Graph of 

 the Log (probit athe- 

 rosclerosis) equation 

 ( equation 2 ) for 

 serum-cholesterol 

 values of 100, 150, 

 200, 250, and 300 

 mg. per 100 ml. 



