Shekelle-Blackburn on Origins of “Low-Fat”
E-mail notes on Dietary Fat issues between Shekelle-Blackburn @2010
RS: Well, here we go, and thanks. But I don’t think saturation is the same as iodine # and ancel was only focused on saturation and chain length.
One application of the iodine number is measuring the unsaturation of fatty acids. The higher the iodine number, the more unsaturated fatty acid bonds are present in a fat.
HB: I RECALL THAT, BUT DIDN’T SEE YOUR CONNECTION. NOW I DO.
RS: One of the hypotheses floating around circa 1950 (and I cannot remember who was proposing it) was that the degree of saturation (as measured by the iodine number) determined the effect of a fat on serum cholesterol concentration. Results by Keys et al and confirmed by Hegsted et al disproved this hypothesis and showed that only three of the fatty acids normally found in food — lauric, myristic, and palmitic acids — affected serum cholesterol concentration. Am I wrong on this?
RS: Normally such evidence — together with results of the Seven Countries Study — would have led to advice to decrease consumption of foods rich in these fatty acids but, despite evidence to the contrary, some persons rather successfully sold the idea that the key to good health was a low-fat diet. (Didn’t the Seven Countries Study find no ecological correlation between CHD incidence and total dietary fat?) I vaguely remember two reasons given for focusing dietary recommendations on total fat. First, the general population was too ignorant to understand dietary advice based on the composition of the fat but they could understand the simple precept — avoid fat. (I don’t remember any evidence offered in support of that idea.) Second, some people thought that dietary fat increased the risk of some cancers and obesity, and that a low-fat diet would have broader benefits than just on CHD. (Wasn’t the evidence in support of those ideas rather weak at the time and hasn’t subsequent work pretty much rendered them obsolete?)
HB: YES AND I THINK STAMLER WAS I THINK IMPORTANTLY RESPONSIBLE FOR THE SIMPLE MESSAGE THAT WAS TRANSLATED INTO THE LOW-FAT MESSAGE THAT PLAGUES US TODAY (TAUBES ET AL.). BUT WE ARE FINDING AMPLE EVIDENCE, IN NEWS ARTICLES, THAT ANCEL, TOO, WENT FOR THAT MESSAGE WHEN HIS WORK SAID OTHERWISE.
RS: With regard to the Greenland Eskimos, I had thought that some consideration was going to be given to the results of studying unusual populations, e.g., Tarahumara Indians, Trappist monks, Bantu, and 7th Day Adventists. Did anything useful come from those studies?
HB: MUCH WAS LEARNED, BUT IT IS NOT WIDELY CITED NOWADAYS. WE WILL HAVE A SEGMENT ON THOSE, BUT QUESTIONS REMAIN ABOUT THE TOKELAU AND THE EAST AFRICAN CHOLESTEROL LEVELS ON APPARENTLY HI-FAT DIETS. CAN YOU SHED INSIGHT ON THE DEPARTURE FROM KEYS PREDICTION ON COCONUT INTAKES AT 60 % CALORIES IN THE TOKELAUANS? THESE WERE EXPLAINED AWAY AS GENETIC DAPTATIONS OF SMALL CULTURAL ISOLATES, AND THE FACT THEIR YEAR-ROUND DIETS WERE INSUFFICIENTLY STUDIED.
RS: Returning to the essay on George Mann’s editorial and the failure to find any association in the Framingham Study with 24-hour diet recalls, wasn’t it the case that most investigators at the time did not understand the effect of unreliability on measures of association? One of Ancel’s contributions was showing that persons within a population could not be reliably distinguished one from the other based on 24-hour diet recalls or diaries or whatever.
HB: INDEED, AND JACOBS AND I DID AN EDITORIAL PIECE ON ZERO CORRELATIONS NOT NECESSARILY EXCLUDING A TRUE RELATIONSHIP.
Jacobs DR, Anderson JT, Blackburn H. Diet and serum cholesterol. Do zero correlations negate the relationship? Amer. J. Epidemiol. 110:77-87, 1979.
RS: Well, enough of my carping. You’re doing the hard work of writing this all down and trying to make sense of it. Best wishes for your success. Rick
HB: YOUR KNOWLEDGE AND COMMENTS WILL BE MOST USEFUL. IT IS SO HARD TO SEPARATE REVIEWING THE SCIENCE (WHICH I SHOULDN’T ATTEMPT AT THIS STAGE) AND THE HISTORY OF THE SCIENCE, BUT YOU POSE SEVERAL ISSUES THAT WERE CRUCIAL IN THE HISTORY.