Wednesday, March 15, 2006

Fats and food fads

Fads and superstitions related to food have been a part of human cultures for a long time. The Old Testament of the Hebrew and Christian Bible, of course, is notorious for nonsense about what is good or bad to eat. For example, Ch. 11 of Leviticus is full of it:
[1] And the LORD spake unto Moses and to Aaron, saying unto them,
[2] Speak unto the children of Israel, saying, These are the beasts which ye shall eat among all the beasts that are on the earth.
[3] Whatsoever parteth the hoof, and is clovenfooted, and cheweth the cud, among the beasts, that shall ye eat.
[4] Nevertheless these shall ye not eat of them that chew the cud, or of them that divide the hoof: as the camel, because he cheweth the cud, but divideth not the hoof; he is unclean unto you.
[5] And the coney, because he cheweth the cud, but divideth not the hoof; he is unclean unto you.
[6] And the hare, because he cheweth the cud, but divideth not the hoof; he is unclean unto you.
[7] And the swine, though he divide the hoof, and be clovenfooted, yet he cheweth not the cud; he is unclean to you.
[8] Of their flesh shall ye not eat, and their carcase shall ye not touch; they are unclean to you.
[9] These shall ye eat of all that are in the waters: whatsoever hath fins and scales in the waters, in the seas, and in the rivers, them shall ye eat.
[10] And all that have not fins and scales in the seas, and in the rivers, of all that move in the waters, and of any living thing which is in the waters, they shall be an abomination unto you:
[11] They shall be even an abomination unto you; ye shall not eat of their flesh, but ye shall have their carcases in abomination.
[12] Whatsoever hath no fins nor scales in the waters, that shall be an abomination unto you.

There follows the same sort of stuff regarding poultry. Yadda, yadda, yadda in this vein to the end of the chapter. Exactly what is so great about animals that have cloven hooves and chew their cud, or bad about animals that don't, is never quite made clear. But then, these are commandments and you're not supposed to understand. Just do it. And truth be told, commandments like these don't hold a candle to some of the atrocities called for elsewhere in Leviticus. Cultures just seem to accumulate this kind of nonsense as they go along.

But that's getting off topic. There are theories about why certain animals were in or out of favor for eating back in the Bronze Age middle east. Probably it had somewhat to do with avoiding animals that tended to harbor unpleasant parasite-caused diseases, of which folks had no understanding at the time. Steven Pinker also suggests that having a taboo on food that your enemies enjoyed was useful for keeping people from sitting down to a friendly meal with those enemies, finding out they weren't such bad sorts after all, and thereby messing up the butchery and general mayhem planned by the military-industrial complex of that place and time.

Fast forward 30 centuries or so. People in the middle east are still passionately engaged in making hamburger of each other. But in parts of the more civilized world, people now expend more passion debating whether or not it's a good idea to eat hamburger at all. And if so, whether a Big Mac® is better than a Whopper®, or whether ground beef with 10% fat is OK, while 20% fat is not.

Fat itself is the subject of much passionate food faddism these days. Until relatively recently in history, it wasn't so much of an issue. Most animals, including humans, faced enough difficulties simply surviving that they had little time to accumulate surpluses of fat. (Except for aquatic mammals like whales and seals which didn't need to worry overly much about the strain on the joints of lugging excess pounds about, and others like bears whose lifestyle of yearly hibernation required storing up calories in large amounts for their annual winter nap.)

Once agricultural technology reached a certain level of efficiency, however, humans discovered that nature had provided them with a fondness for fat in the diet, long before the discovery of Big Macs and fries. Evidently, nature did this because there were actually benefits that accrued from consuming a judicious amount of fat in one's diet, as a means of storing up calories which were so abundant on the occasion that the tribe's hunters succeeded in bagging a mammoth or two, to tide everyone over leaner times when all the mammoths in the area seemed to have left for the Poconos.

But eventually, some clever epidemiologists in N. America noticed that people from parts of the world where diseases like cancer and atherosclerosis were rare soon started suffering from such diseases at rates comparable to those of the natives awhile after the immigrants had relocated to places where consumption of a "western diet" (2 lb. steaks and baked potatoes with sour cream) was the norm. Putting two and two together, it was decided that the cause of this phenomenon was probably too much fat in the diet.

Thus was born the doctrine that fat in the diet is a Bad Thing. The medical community was not long in accepting this idea. It became the conventional wisdom in recent decades. There was even a lot of evidence for some of the apparent ill effects of excess fat in the diet, particularly various forms of cardiovascular disease.

The evidence for an association between high-fat diets and cancer was thought to be there too. The AMA endorsed the idea. For example, their Family Health Cookbook stated bluntly
Maintaining your optimal body weight is important because being overweight elevates the risk for certain types of cancer, such as colon cancer (cancer of part of the large intestine), in men and women. Carrying a lot of weight in the abdomen has been linked to an increased risk of breast cancer in women.

Some physicians took these concerns very seriously indeed, and some among them championed the cause of the Low Fat Diet. One among that number is Dr. John McDougall, who has written extensively on healthy diet -- low-fat diets, in particular. His McDougall Report, for example, states
• The high fat Western diet is the leading cause of cancer, contributing most directly to cancer of the colon, breast, and prostate, but also to other cancers (Lancet 340:162, 1992).
• Cancers common in the Western world are rare in countries where a starch-based diet is still followed. However, as people in these countries change their eating habits, they develop our cancers. For example, breast cancer in Japan is expected to move from the fifth most common cancer among women to number one in the next ten years (Cancer 67:2021, 1991).

The leading cause? Really? That's a pretty strong statement. Does science actually support that... or are we seeing a bit of creeping food faddism? Indeed, in recent years champions have, in fact, emerged for the virtues of low-carbohydrate, high-protein diets, which are almost the opposite of what McDougall recommends. Of course, the high-protein diet is lauded for weight loss more than prevention of diseases like cancer, but still... what's a person to believe about what's good or bad as a healthy diet?

Moreover, cancer is now known to be mainly a disease (a whole family of diseases, actually) that results from DNA defects which eventually lead to uncontrolled cell proliferation. (See here.) So why would excess fat in the diet be the leading cause of cancer? Exactly how good is the scientific evidence for such a conclusion?

Not very good, as it turns out. Not very good at all:

Reducing Total Fat Intake May Lower Breast-Cancer Risk But Has Little Impact on Risk of Colon Cancer or Heart Disease
Feb. 7, 2006 — Adopting a low-fat diet in later life and following such a regimen for nearly a decade does not appear to have a significant impact on reducing the overall risk of breast cancer, colorectal cancer or heart disease, according to a Women's Health Initiative study that involved nearly 50,000 postmenopausal women across the United States.

Here are some additional articles on this research:

This research is not without its problems. Some of the criticisms:

  • Only post-menopausal women were studied, not younger women or any men.
  • The study lasted "only" eight years, possibly not long enough to show much effect.
  • The target for reduction of fat in the diet was low (to 20% of consumed calories, where 10% might have been better), and many participants didn't achieve the target.
  • No effort was made to focus on specific components in the diet, such as cholesterol, instead of overall fat consumption.

Gina Kolata in the New York Times has a lengthy article (Maybe You're Not What You Eat) on the subject putting it all in the context of food faddism, and especially in relation to common beliefs in American culture.
"It's one of the great principles — no, more than principles, canons — of American culture to suggest that what you eat affects your health," says James Morone, a professor of political science at Brown University.

"It's this idea that you control your own destiny and that it's never too late to reinvent yourself," he said. "Vice gets punished and virtue gets rewarded. If you eat or drink or inhale the wrong things you get sick. If not, you get healthy."

That very American canon, he and others say, may in part explain the criticism and disbelief that last week greeted a report that a low-fat diet might not prevent breast cancer, colon cancer or heart disease, after all.

The report, from a huge federal study called the Women's Health Initiative, raises important questions about how much even the most highly motivated people can change their eating habits and whether the relatively small changes that they can make really have a substantial effect on health.

So what's next? Where do we go from here? Is what we need a study with twice as many participants, including men as well as women? Should it start with much younger people and run for 20 or 30 years? That's bound to be quite expensive -- and a lapse of time extending an entire generation.

It occurs to me that a better idea, or at least something additional to try, is to zero in on the exact mechanisms through which dietary fats of particular types affect the development of specific cancers. The goal should be to determine exactly what it is that's harmful about specific types of fat in the diet, in the same way we study other carcinogens and other factors that cause DNA damage.

Here are a couple of recent studies that take this approach:

Not only would such research probably produce results more quickly, but it offers the hope of results that are more useful in preventing cancer. Rather than assuming only a major lifestyle change will suffice -- a change which could be just too difficult to be adopted widely enough -- perhaps we can discover medicines or other more targeted means to overcome the specific effects of dietary fat that are most likely to lead to cancer.

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