The Melting of the Lipid Hypothesis
Nutritionism is good for the food business. But is it good for us? You might think that a national fixation on nutrients would lead to measuable improvements in public health. For that to happen, however, the underlying nutritional science and the policy recommendations (not to mention the journalism) based on that science would both have to be sound. This has seldom been the case.
The most important such nutrition campaign has been the thirty-year effort to reform the food supply and our eating habits in light of the lipid hypothesis - the idea that dietary fat is responsible for chronic disease. At the behest of government panels, nutrition scientists, and public health officials, we have dramatically changed the way we eat and the way we think about food, in what stands as the biggest expriment in applied nutritionism in history. Thirty years later, we have good reason to believe that putting the nutritionists in charge of the menu and the kitchen has not only ruined an untold number of meals, but also has done little for our health, except very possibly to make it worse.
These are strong words, I know. Here are a couple more: What the Soviet Union was to the ideology of Marxism, the Low-Fat Campaign is to the ideology of nutritionism - its supreme test and, as nw is coming clear, it's most abject failure. You can argue, as some diehards will do, that th eproblem was one of faulty execultion or you can accept that the underlying tenets of the ideology contained the seeds of the eventual disaster.
At this point you're probably saying to yourself, Hold on just a minute. Are you really saying the whole low-fat deal was bogus? But my supermarket is still packed with low-fat this and no-cholesterol that! My doctor is still on me about my cholesterol and telling me to switch to low-fat everything. I was flabbergasted at the news too, because no one in charge - not in the government, not in the public health community - has dared to come out and announce: Um, you know everything we've been telling you for the last thirty years about the links between dietary fat and heart disease? And fat and cancer? And fat and fat? Well, this just in: It now appears that none of it was true. We sincerely regret the error.
No, the admissions of error have been muffled, and the mea culpas impossible to find. But read around in the recent scientifid literature and you will find a great many scientists beating a quiet retreat from the main tenets of the lipid hypothesis. Let me offer just one example, an article from a group of prominent nutrition scientists at the Harvard School of Public Health. In a recent review of the relevant research called "Types of Dietary Fat and Risk of Coronary Heart Disease: A Critical Review,"* the authors proceed to calmly remove, one by one, just about every strut supporting the theory that dietary fat causes heart disease.
*Frank B. Hu, et al., Journal of the American College of Nutrition, Vol. 20, 1, 5-19 (2001)
Hu and his colleagues begin with a brief, uninflected summary of the lipophobic era that is noteworthy mostly for casting the episode in the historical past:
During the past several decades, reduction in fat
intake has been the main focus of national
dietary recommendations. In the public's mind, the
words "dietary fat" have become synonymous with
obesity and heart disease, whereas the words
"low-fat" and "fat-free" have been symonymous
with heart health.
We can only wonder how in the world such crazy ideas ever found their way into the "public's mind". Surely not from anyone associated with the Harvard School of Public Health, I would hope. Well, as it turns out, the selfsame group, formerly in thrall to the lipid hypothesis, was recommending until the early 1990s, when the evidence about the dangers of trans fats could no longer be ignored, that people reduce their saturated fat intake by switching from butter to margarine. (Though red flags about trans fats can be spooted as far back as 1956, when Ancel Keyes, the father of the lipid hypothesis, suggested that rising consumption fo hydrogenated vegetable oils might be responsible for the twentieth-century rise in coronary heart disease.)
But back to the critical review, which in its second paragraph drops this bombshell:
It is now increasingly recognised that the low-fat
campagin has been based on little scientific
evidence and may have caused unintended health consequences.
Say what?
The article then goes on blandly to survey the crumbling foundations of the lipid hypothesis, circa 2001: Only two studies have ever found "a significant positive association between saturated fat intake and risk of CHD [coronary heart disease]"; many more have failed to find an association. Only one study has ever found "a significant inverse association between polyunsaturated fat intake and CHD." Let me translate: The amount of saturated fat in the diet may have little if any bearing on the risk of heart disease, and evidence that increasing polyunsaturated fats in the diet will reduce risk is slim to nil. As for the dangers of dietary cholesterol, the review found "a weak and nonsignificant positive association between dietary cholesterol and risk of CHD." (Someone should tell the food processors, who continue to treat dietary cholesterol as a matter of life and death.) "Surprisingly," the authors wrote, "there is little direct evidence linking higher egg consumption and increased risk of CHD" - surprising, because eggs are particularly high in cholesterol.
By the end of the review there is one strong association between a type of dietary fat and heart disease left standing, and it happens to be precisely the type of fat that the low-fat campaigners have spend most of the last thirty years encouraging us to consume more of: trans fats. It turns out that "a higher intake of trans fat can contribute to increased risk of CHD through multiple mechanisms"; to wit, it raises bad cholesterol and lowers good cholesterol (something not even the evil saturated fats can do); it increases triglycerides, a risk factor for CHD; it promotes inflammation and possibly thrombogenesis (clotting), and it may promote insulin resistance. Trans fat is really bad stuff, apparently, fully twice as bad as saturated fat in its impact on cholesterol ratios. If any of the authors of the critical review are conscious of the cosmic irony here - that the principal contribution of thirty years of official nutritional advice has been to replace a possibly mildly unhealthy fat in our diets with a demonstrably lethal one - they are not saying.
The paper is not quite prepared to throw out the entire lipid hypothesis, but by the end precious little of it is left standing. The authors conclude that while total levels of fat in the diet apparently have little bearing on the risk of heart disease (!), the ration between types of fats does. Adding omega-3 fatty acids to the diet (that is, eating more of a certain kind of fat) "substantially reduces coronary and total mortality" in heart patients, and replacing saturated fats with polyunsaturated fats lowers blood cholesterol, which they deem an important risk factor for CHD. (Some researchers no longer do, pointing out that half the people who get heart attacks don't have elevated cholesterol levels, and about half the people with elevated cholesterol do not suffer from CHD.) One other little grenade is dropped in the paper's conclusion: Although "a major purported benefit of a low-fat diet is weight loss," a review of the literature failed to turn up any convincing evidence of this proposition. To the contrary, it found "some evidence" that replacing fats in the diet with carbohydrates (as official dietary advice has urged us to do since the 1970s) will lead to weight gain.
I have dwelled on this paper because it fairly reflects the current thinking on the increasingly tenuous links between dietary fat and health. The lipid hypothesis is quietly melting away, but no one in the public health community, or the government, seems quite ready to publicly acknowledge it. For fear of what exactly? That we'll binge on bacon double cheeseburgers? More likely that we'll come to the unavoidable conclusion that the emperors of nutrition have no clothes and never listen to them again.
We can only hope. Extract from In Defence of Food by Michael Pollan, which I highly recommend. This rant in the form of a book extract brought to you by the appearance tonight of an advertisement pushing margarine by guilt/fear tripping parents with the image of all that saturated animal fat from butter going into their children's arteries. *headdesk*
The most important such nutrition campaign has been the thirty-year effort to reform the food supply and our eating habits in light of the lipid hypothesis - the idea that dietary fat is responsible for chronic disease. At the behest of government panels, nutrition scientists, and public health officials, we have dramatically changed the way we eat and the way we think about food, in what stands as the biggest expriment in applied nutritionism in history. Thirty years later, we have good reason to believe that putting the nutritionists in charge of the menu and the kitchen has not only ruined an untold number of meals, but also has done little for our health, except very possibly to make it worse.
These are strong words, I know. Here are a couple more: What the Soviet Union was to the ideology of Marxism, the Low-Fat Campaign is to the ideology of nutritionism - its supreme test and, as nw is coming clear, it's most abject failure. You can argue, as some diehards will do, that th eproblem was one of faulty execultion or you can accept that the underlying tenets of the ideology contained the seeds of the eventual disaster.
At this point you're probably saying to yourself, Hold on just a minute. Are you really saying the whole low-fat deal was bogus? But my supermarket is still packed with low-fat this and no-cholesterol that! My doctor is still on me about my cholesterol and telling me to switch to low-fat everything. I was flabbergasted at the news too, because no one in charge - not in the government, not in the public health community - has dared to come out and announce: Um, you know everything we've been telling you for the last thirty years about the links between dietary fat and heart disease? And fat and cancer? And fat and fat? Well, this just in: It now appears that none of it was true. We sincerely regret the error.
No, the admissions of error have been muffled, and the mea culpas impossible to find. But read around in the recent scientifid literature and you will find a great many scientists beating a quiet retreat from the main tenets of the lipid hypothesis. Let me offer just one example, an article from a group of prominent nutrition scientists at the Harvard School of Public Health. In a recent review of the relevant research called "Types of Dietary Fat and Risk of Coronary Heart Disease: A Critical Review,"* the authors proceed to calmly remove, one by one, just about every strut supporting the theory that dietary fat causes heart disease.
*Frank B. Hu, et al., Journal of the American College of Nutrition, Vol. 20, 1, 5-19 (2001)
Hu and his colleagues begin with a brief, uninflected summary of the lipophobic era that is noteworthy mostly for casting the episode in the historical past:
During the past several decades, reduction in fat
intake has been the main focus of national
dietary recommendations. In the public's mind, the
words "dietary fat" have become synonymous with
obesity and heart disease, whereas the words
"low-fat" and "fat-free" have been symonymous
with heart health.
We can only wonder how in the world such crazy ideas ever found their way into the "public's mind". Surely not from anyone associated with the Harvard School of Public Health, I would hope. Well, as it turns out, the selfsame group, formerly in thrall to the lipid hypothesis, was recommending until the early 1990s, when the evidence about the dangers of trans fats could no longer be ignored, that people reduce their saturated fat intake by switching from butter to margarine. (Though red flags about trans fats can be spooted as far back as 1956, when Ancel Keyes, the father of the lipid hypothesis, suggested that rising consumption fo hydrogenated vegetable oils might be responsible for the twentieth-century rise in coronary heart disease.)
But back to the critical review, which in its second paragraph drops this bombshell:
It is now increasingly recognised that the low-fat
campagin has been based on little scientific
evidence and may have caused unintended health consequences.
Say what?
The article then goes on blandly to survey the crumbling foundations of the lipid hypothesis, circa 2001: Only two studies have ever found "a significant positive association between saturated fat intake and risk of CHD [coronary heart disease]"; many more have failed to find an association. Only one study has ever found "a significant inverse association between polyunsaturated fat intake and CHD." Let me translate: The amount of saturated fat in the diet may have little if any bearing on the risk of heart disease, and evidence that increasing polyunsaturated fats in the diet will reduce risk is slim to nil. As for the dangers of dietary cholesterol, the review found "a weak and nonsignificant positive association between dietary cholesterol and risk of CHD." (Someone should tell the food processors, who continue to treat dietary cholesterol as a matter of life and death.) "Surprisingly," the authors wrote, "there is little direct evidence linking higher egg consumption and increased risk of CHD" - surprising, because eggs are particularly high in cholesterol.
By the end of the review there is one strong association between a type of dietary fat and heart disease left standing, and it happens to be precisely the type of fat that the low-fat campaigners have spend most of the last thirty years encouraging us to consume more of: trans fats. It turns out that "a higher intake of trans fat can contribute to increased risk of CHD through multiple mechanisms"; to wit, it raises bad cholesterol and lowers good cholesterol (something not even the evil saturated fats can do); it increases triglycerides, a risk factor for CHD; it promotes inflammation and possibly thrombogenesis (clotting), and it may promote insulin resistance. Trans fat is really bad stuff, apparently, fully twice as bad as saturated fat in its impact on cholesterol ratios. If any of the authors of the critical review are conscious of the cosmic irony here - that the principal contribution of thirty years of official nutritional advice has been to replace a possibly mildly unhealthy fat in our diets with a demonstrably lethal one - they are not saying.
The paper is not quite prepared to throw out the entire lipid hypothesis, but by the end precious little of it is left standing. The authors conclude that while total levels of fat in the diet apparently have little bearing on the risk of heart disease (!), the ration between types of fats does. Adding omega-3 fatty acids to the diet (that is, eating more of a certain kind of fat) "substantially reduces coronary and total mortality" in heart patients, and replacing saturated fats with polyunsaturated fats lowers blood cholesterol, which they deem an important risk factor for CHD. (Some researchers no longer do, pointing out that half the people who get heart attacks don't have elevated cholesterol levels, and about half the people with elevated cholesterol do not suffer from CHD.) One other little grenade is dropped in the paper's conclusion: Although "a major purported benefit of a low-fat diet is weight loss," a review of the literature failed to turn up any convincing evidence of this proposition. To the contrary, it found "some evidence" that replacing fats in the diet with carbohydrates (as official dietary advice has urged us to do since the 1970s) will lead to weight gain.
I have dwelled on this paper because it fairly reflects the current thinking on the increasingly tenuous links between dietary fat and health. The lipid hypothesis is quietly melting away, but no one in the public health community, or the government, seems quite ready to publicly acknowledge it. For fear of what exactly? That we'll binge on bacon double cheeseburgers? More likely that we'll come to the unavoidable conclusion that the emperors of nutrition have no clothes and never listen to them again.
We can only hope. Extract from In Defence of Food by Michael Pollan, which I highly recommend. This rant in the form of a book extract brought to you by the appearance tonight of an advertisement pushing margarine by guilt/fear tripping parents with the image of all that saturated animal fat from butter going into their children's arteries. *headdesk*