New York has recently banned trans fats in food and many other places are thinking of following suit. So fat is yet again a political issue. But is the trans fats scare just another example of hysteria fanned by attention-seekers?
It is easy to see why the medical profession is generally critical of dietary trans fats. The medical gurus are nearly as critical of trans fats as they once were of dietary cholesterol. If you give people a heap of trans fats to eat in some form and then check their blood chemistry a couple of hours later, the changes observed are indeed in the direction associated with heart disease. For many in the medical profession, that is all the evidence you need to condemn trans fats in the diet. Old hands however are aware that there is no end of medical studies based on short term observations of some factor in isolation (also usually associated with atypically high doses of something) which generate either panics or enthusiasms but which later find no support when one looks at long term or overall effects in epidemiology or in better conducted studies.
And intellectual fashions have an alarming tendency to be self-reinforcing. The only kind of study which could settle the question of long term overall ill-effects from trans fats is of course a double-blind prospective study -- where normal, average healthy people are divided into two groups and over a long period fed diets that differ only in trans fat content. You then see how many die in each group in the given period. Drug evaluation research routinely uses such studies but in the case of trans fats, such research has recently been declared "unethical" (See D. Mozaffarian, M. B. Katan, A. Ascherio, M. J. Stampfer, and W. C. Willett. "Trans Fatty Acids and Cardiovascular Disease" N.Engl.J.Med., 2006, 354:1601-1613) and nobody seems to be doing it. It must be comforting to rule out in advance research that could prove you wrong. It is at least dogmatic and arrogant (though parading as compassionate, of course).
It is perhaps because of the lack of proper prospective studies and the need for the prevailing religion to be reinforced that the medical literature is replete with review articles that stress the evils of trans fats. And each new review quotes a lot from previous reviews. The image it all calls to my mind is of one turtle clinging to the back of another turtle who is clinging to the back of another turtle who is clinging to the back of another turtle. One can only hope that the bottom turtles (research reports) are standing on something solid. Knowing how often medical journal articles overlook important confounding variables like social class I doubt it of course. As a humble retired psychologist who comes to this field out of an interest in the sociology of knowledge, I have neither the time nor the ease of access to look at the multitude of bottom turtles concerned but I do notice something about the reviews: It is notable that the most recent reviews are the most definite and mention fewer "non-conforming" research results.
I thought it might be interesting therefore to reproduce the epidemiology section of an older (1999) review so that readers can see that there are many studies which do not show ill effects of such fats and which mention many doubts about those studies which do show ill effects (Quote: "Interpretation of comparisons among populations with widely different lifestyles is hazardous"). The authors still come to the conclusion that theory and short-term observations would suggest but it is of course the long-term and overall effect of trans fat ingestion that is the issue -- hence the interest of epidemiological studies.
It is easy to see why the medical profession is generally critical of dietary trans fats. The medical gurus are nearly as critical of trans fats as they once were of dietary cholesterol. If you give people a heap of trans fats to eat in some form and then check their blood chemistry a couple of hours later, the changes observed are indeed in the direction associated with heart disease. For many in the medical profession, that is all the evidence you need to condemn trans fats in the diet. Old hands however are aware that there is no end of medical studies based on short term observations of some factor in isolation (also usually associated with atypically high doses of something) which generate either panics or enthusiasms but which later find no support when one looks at long term or overall effects in epidemiology or in better conducted studies.
And intellectual fashions have an alarming tendency to be self-reinforcing. The only kind of study which could settle the question of long term overall ill-effects from trans fats is of course a double-blind prospective study -- where normal, average healthy people are divided into two groups and over a long period fed diets that differ only in trans fat content. You then see how many die in each group in the given period. Drug evaluation research routinely uses such studies but in the case of trans fats, such research has recently been declared "unethical" (See D. Mozaffarian, M. B. Katan, A. Ascherio, M. J. Stampfer, and W. C. Willett. "Trans Fatty Acids and Cardiovascular Disease" N.Engl.J.Med., 2006, 354:1601-1613) and nobody seems to be doing it. It must be comforting to rule out in advance research that could prove you wrong. It is at least dogmatic and arrogant (though parading as compassionate, of course).
It is perhaps because of the lack of proper prospective studies and the need for the prevailing religion to be reinforced that the medical literature is replete with review articles that stress the evils of trans fats. And each new review quotes a lot from previous reviews. The image it all calls to my mind is of one turtle clinging to the back of another turtle who is clinging to the back of another turtle who is clinging to the back of another turtle. One can only hope that the bottom turtles (research reports) are standing on something solid. Knowing how often medical journal articles overlook important confounding variables like social class I doubt it of course. As a humble retired psychologist who comes to this field out of an interest in the sociology of knowledge, I have neither the time nor the ease of access to look at the multitude of bottom turtles concerned but I do notice something about the reviews: It is notable that the most recent reviews are the most definite and mention fewer "non-conforming" research results.
I thought it might be interesting therefore to reproduce the epidemiology section of an older (1999) review so that readers can see that there are many studies which do not show ill effects of such fats and which mention many doubts about those studies which do show ill effects (Quote: "Interpretation of comparisons among populations with widely different lifestyles is hazardous"). The authors still come to the conclusion that theory and short-term observations would suggest but it is of course the long-term and overall effect of trans fat ingestion that is the issue -- hence the interest of epidemiological studies.
See the excerpt fron the study here - (a post of Dec. 19).
No comments:
Post a Comment