Quantifying Dietary Fat Effects on Serum Cholesterol in Controlled Diets
A 1965 study by D. M. Hegsted, R. B. McGandy, M. L. Myers and F. J. Stare examined how changes in dietary fatty-acid composition and cholesterol intake related to serum cholesterol in men during repeated controlled diet periods.
What the study did and found
The 1965 paper “Quantitative effects of dietary fat on serum cholesterol in man” investigated how individual components of dietary fat were associated with changes in serum cholesterol. The study involved 20 men aged 38–57, divided into groups of nine and eleven. Each group completed 18 dietary periods lasting four weeks, allowing repeated comparisons while the amount and composition of dietary fat were systematically changed.
The investigators varied particular fatty acids while keeping other dietary factors as consistent as possible. Fat supplied either about 22% or 37–40% of total energy, while protein supplied approximately 15–16%. Dietary cholesterol was generally controlled within each period and deliberately altered during selected periods. Blood lipid measurements were collected repeatedly, and multiple regression was used to examine relationships between fatty-acid intake, dietary cholesterol and serum cholesterol.
Changes in myristic acid, palmitic acid, polyunsaturated fatty acids and dietary cholesterol together explained 91% of the variance in serum cholesterol observed during the experiment. Myristic acid had the strongest positive association, while palmitic acid had a smaller positive effect. Higher polyunsaturated fatty-acid intake was associated with lower serum cholesterol. An additional 100 mg of dietary cholesterol corresponded to an increase of about 5 mg% in serum cholesterol under the conditions studied.
Why it is cited
Hegsted and colleagues quantified the effects of individual fatty acids rather than treating dietary fat as a single nutritional variable. Controlled diets and regression analysis allowed myristic acid, palmitic acid, polyunsaturated fatty acids and dietary cholesterol to be examined separately.
Repeated dietary periods in the same participants also allowed fatty-acid composition to be compared with total fat intake. Serum cholesterol varied more closely with the composition and proportions of dietary fatty acids than with the total amount of fat consumed during the experiment.
The study included 20 men aged 38–57 from a single institutional setting, and most participants had chronic schizophrenia. Dietary periods lasted four weeks, and the regression equation was derived from measurements collected under these controlled conditions. Its results cannot be assumed to apply equally to other populations or dietary settings. The reported 91% value refers to variation in serum cholesterol explained within this experiment. It does not indicate that the four dietary variables explain 91% of serum-cholesterol variation in the general population. The increase of approximately 5 mg% associated with an additional 100 mg of dietary cholesterol was also an average observed under the experimental conditions rather than a fixed response for every individual. |
The topic today
The 1965 experiment contributed to a more detailed understanding of dietary fats by separating the effects of individual fatty acids from total fat intake. This approach helped establish the importance of fatty-acid composition when examining changes in blood lipids.
The experiment measured relatively short-term serum-lipid responses in a small group of men and did not assess long-term cardiovascular outcomes. Its quantitative analysis remains historically significant, while the limited sample, controlled setting and short dietary periods restrict how broadly its numerical estimates can be applied.