Abstract: The Life Ahead formula relating serum or blood cholesterol to dietary factors as dietary fats, cholesterol, and fiber was based on Global analyses of results on diets of up to several hundred different populations. Saturated fats usually are a most important factor increasing serum cholesterol, with dietary cholesterol and transfat contributing further. Polyunsaturated fats and fiber can reduce serum cholesterol substantially and most mono-unsaturated fat will reduce serum cholesterol slightly. The specific content of fiber and each type of fat in a food produces complex and interdependent effects on the serum cholesterol of a diet to which it is added or subtracted. Thus any analysis of diet should recognize the summed effects on health of all nutrients included in all foods and dietary supplements present.
Background: The relationship between dietary fats and serum cholesterol and heart disease competes with cigarette smoking as a most studied of all subjects of health during the last half century. A Medline search brings up more than 38,000 involved research studies. Extensive study was devoted to the Life Ahead Global Model of this subject that follows in this and other discussions of Life Ahead. First was the obtaining of a relationship of fats to cholesterol, and second is an answer to the question “Does this cholesterol relationship explain how dietary fats produce differences in heart disease?” The discussion following here addresses the first of these questions. For the second question, see Dietary Fats and Heart Disease.
Total Fat does not measure Health Value: Dietary fat has been much heralded as a “Terrible Negative” to health. This is not always true. Today we know that saturated fats are ‘bad’ but polyunsaturated fats are ‘good' and that most unsaturated fats are modestly beneficial. Thus we must know the specific composition of fats to value their effect on health. And each time we change the amount of one fat, the amounts of two or three other fats are also changed. No food includes just one kind of fat. Thus a valuation of how dietary fats change cholesterol becomes quite complex. A second problem is that usual margin of error of individual measurements of fats on cholesterol are very high relative to the accuracy of answers needed. Thus we need to obtain averaged results from many different comparisons to obtain useful values.
Fortunately, we now do have two useful Global level analyses of how various fats produce cholesterol. A first was that of Hegsted (Am J Clin Nutr 57:875) and a second by Mensink (Arteriosclerosis and Thrombosis 12:911). Hegsted put together a summary analysis from 420 dietary measurements on 141 different populations. Mensink included results of 65 comparisons for 27 trials. The results from these extensive analyses were used in designing the relationship adopted for Life Ahead.
The Life Ahead Formula: The present formula estimates - as is done for all other factors in Life Ahead - differences in total serum cholesterol from that of an average US population. The basic model of risk from cardiovascular diseases uses total serum cholesterol and HDL concentration in this total as bases to forecast progression of disease. The average levels of dietary factors used in the average population file are 13% saturated fat, 16% monounsaturated fat, 8.5% polyunsaturated fat, 1.2% of transfat, 160 mg/day of dietary cholesterol, and 18 daily grams of fiber. The values for transfats used here as discussed elsewhere probably are lower than actual, but are consistent with transfat values in the Life Ahead diet library. Average total cholesterol in mg/dl at age 50 is taken as 213 for men and 218 for women for the base population file. Differences in estimated total serum or blood cholesterol in mg/dl from these average values are computed from % values of fats and fiber and mg of dietary cholesterol in diets as:
Diff Total Cholesterol, mg/dl = 1.4 * (% sat fat - 13) - 0.3 * (% monounsatfat - 16)
- 0.8 * (% polyfat - 8.5) + 1.5 * (% transfat – 1.2)
+ 0.06 * (dietary cholesterol, mg - 160) - 1.2 * (% Fiber - 18)
The formula produces a zero difference in cholesterol from the above population values at the average basis values of all included factors. It includes a small negative (desirable) credit to cholesterol for added unsaturated fats in agreement with Mensink. The additional of effects on cholesterol for dietary cholesterol and fiber are based on Life Ahead analyses of these factors, each of which can significantly affect serum cholesterol levels.
The most important usual determinant of serum cholesterol is saturated fat. The above formulas values are in agreement with values from the classic research of Keys (Am J Clin Nutr 19:175). The above formula under-predicts the Keys formula values somewhat for saturated fat per se. But when including the usual added amounts of dietary cholesterol that accompany increases in saturated fat, this formula produces results in good agreement with the Keys study. Dietary fiber also can have a very important effect on serum cholesterol that today is not usually recognized. A maximum total serum cholesterol from diet is now set arbitrarily at 250 because of inadequate data at higher serum cholesterol values.
The adequacy and accuracy of this formula in forecasting the risk of Dietary Fats on coronary heart disease is discussed further in Dietary Fats and Heart Disease.
Diet and HDL Cholesterol: Hegsted concluded that a useful effect of dietary fat on HDL could not be obtained. Mensink did produce formulas for fats from both HDL per se and HDL/LDL ratios. But use of his formulas failed to produce consistent values for different diets. Also use of these HDL formulas in forecasting effects of fats on heart disease produced unsatisfactory and variable results. A problem is that small computed differences in HDL vs. LDL or total cholesterol values from diets can produce large differences in forecast risk of heart disease that are widely inconsistent with their known effects on disease. A study of effects of diet on HDL suggested that dietary factors other than alcohol probably do not change the percentage of HDL in total Cholesterol very much. The data found relating dietary fat to serum HDL cholesterol were not adequate either to refute this or to supply a useful alternative. Life Ahead now assumes that there is no effect of usual dietary foods or supplements on the HDL concentration in total cholesterol. Note that use of statistical ratios such as HDL/LDL or Total Cholesterol/HDL can produce inconsistent values that may not relate well to the more probably valid biochemical basis of HDL concentration in total cholesterol used in Life Ahead.
The effect of unsaturated fat on serum cholesterol probably could be refined in the future because individual C12, C14, and C18 fats can have quite differing effects on serum cholesterol. The present formula also is an approximation that does not recognize that dietary differences probably will produce a larger effect on cholesterol at high cholesterol levels than at low cholesterol levels. No basis for quantifying an effect for this logical factor was found. But the present formula appears to forecast well the health risks on various foods as is shown herein in other discussions. If some other dietary factor can be shown with adequate accuracy to change the HDL concentration in cholesterol, this can contribute further and will be recognized in Life Ahead.
Life Ahead produces an estimate of a user's serum cholesterol from the above formula with entered diet at present age. This value is displayed in the output analysis shown for a diet entry. When first estimating this result for a program user that has entered an actual serum cholesterol value, the program asks if the entered diet is that usual for the user when the serum cholesterol was obtained. If this question is answered Yes, the program will compute a cholesterol genetic factor that recognizes a difference between computed and actual cholesterol level for this user. This genetic factor is then recorded and used to adjust the user's estimated serum cholesterol from diet to a more likely actual level. For example, if a person has a genetic factor below 1.0, or has a more favorable actual cholesterol than that computed from the above formula, all values for estimated serum cholesterol of this user will be adjusted downward by the genetic factor. The demo program in Life Ahead assumes that the user has an average population serum cholesterol at age, and thus provides directly results using the above formula values.
Diet Valuations Require Consideration of ALL Nutrients: Most recommended diets in diet books favor one selected key factor, as for example, low fat, or low carbohydrate, high protein, etc. An analysis of such diets for long range health and Well-Days reveals that most are seriously flawed. For example, an example of a very low fat diet recommended by Pritikin was found to include seriously inadequate amounts of both fiber and antioxidants. (Daily Diet #1 in the Life Ahead Demo). The net health value and estimated cholesterol of this diet computed little better than that of a population average diet. An example diet of Atkins (Daily Diet #4 in the Demo) produced a very high amount of saturated fat and forecast serum cholesterol. Yet despite this, this proposed diet although still seriously deficient in potential Well-Days near equaled that of the Pritikin low fat example because it included more adequate fiber and antioxidants. See the Life Ahead Well-Days valuation of 11 quite different proposed diets.
Life Ahead shows repeatedly the importance of including ALL NUTRIENTS possible in any analysis of a diet. Focusing only on a presumed value of just one nutrient can bring in unexpected offsetting deficiencies of other nutrients that thwart the overall health objective desired. Further, Life Ahead reveals further how diets can be modified to accomplish a much more healthful outcome by including optimum values of up to 20 included nutrients.