Sunday, February 12, 2012

Extreme Diets: Perfect for Reality TV

I wrote my last blog post, Moving towards a whole foods, plant-based diet, after earning a degree in Public Health that focused on chronic disease etiology and prevention. Then I accidentally bumped into a book called The China Study. When I read that book, little did I know I would be thrown into a storm of nutritional chaos theory in which academics are coming to blows over which diets work, how to lose weight, or whether one can even lose weight at all. My professors didn’t even mention this controversy.  Here is my take on this contentious issue.

The basic controversy can be split into two major groups, the “meat is bad” group and the “meat is good” group. Yes, I know it is a bit more complicated than that, but in lieu of writing a dissertation I am simplifying the arguments. Nestled within the “meat is bad” crowd, you have the low fat people, some of whom eat chicken and pork but steer clear of red meats, some vegetarians—which include every imaginable dietary configuration—and the extremists, the vegans. They are pitted against the “meat is good” group, among whom you will find the anti-carb Atkins crowd, the just-plain-carnivorous steak-a-day people, and the ultimate in carnivore, the Paleo-people, some of whom actually run down their own food with spears.

Meat is Bad

First, let’s look at the low fat “meat is bad” crowd. I think it is pretty intuitive that meat feels unhealthy. It is slower to digest, and fat is clearly visible on the product. So it is not too hard to see their basic argument: fat from animals is high in saturated fats, the kind of fat that clogs your arteries, and, putatively, is a major cause of heart attacks. There are many observational studies that support this claim. However, the evidence is highly inconsistent. Two important details often skirted over are that meat has lots of the good fat, too, and that carbohydrates can affect blood cholesterol levels as much as meat.  We also can’t overlook the fact that high consumption of meat is associated with colon cancer. The mechanism is not fully understood, and it could be the nitrates in preserved meats and not the actual meat that causes colon cancer. Also, there are concerns that cows are an inefficient food source because the inputs (feed) outweigh their outputs (meat). So if everyone were a vegetarian, food costs would be lower and the world would be a better place. But the purpose of this paper is to discuss heart disease and obesity.

One troubling flaw in the “meat is bad” argument is that Americans have been eating less red meat and less saturated fat since the low-fat craze of the 1980s, yet obesity has risen to epidemic proportions. It is also a fact that when people switch to a low-fat diet they increase their carb intake. In addition, there is recent research showing that cutting out too much protein lowers lean muscle mass, which is not a good thing.
Then there is the issue of dairy. When people become vegetarian, most think they have signed on to a healthier lifestyle when, in fact, they often replace their meat consumption with dairy, in the form of cheese, milk, cream sauces, etc.  India is the country with the highest prevalence of vegetarians. Vegetarianism has been integrated into Hindu religious practices and culture for thousands of years, and people there get most of their protein from lentils and dairy. Yet India has the highest levels of diabetes and obesity in the world.

Then there is veganism. Vegans disavow all meat, dairy, and other animal products, and they are seen as higher up on the dietary purity pyramid. I have eaten in many vegan and vegetarian restaurants. Anecdotally, I find that many of these dishes have high levels of salt and/or sugar. I think this is because evolutionarily our palettes are wired for salty, sweet, bitter, and sour, and our cells need fat to rebuild. So we have evolved to crave these tastes, and when you eliminate one of those tastes, you need to replace it with more of another.  
But the real clincher in my questioning of the “meat is bad” perspective comes from the science. In 2010, a thorough meta-analysis published in a prestigious nutrition journal pooled the results of 21 well-regarded studies on saturated fats and health. It showed no significant effect in the relationship between saturated fats and risk of CHD or stroke.  This is definitely a big blow towards the "conclusion" that a low-fat diet is a healthy diet. It also demonstrates how intractable nutritional dogma is because the low-fat diet is still taught in medical schools and health science departments and appears in guidelines used by public schools.

These two dietary choices seem to be based more on romance than evidence, from the health perspective. (I realize there are other reasons, such as ethics and environmentalism, that people choose these diets.) I was never able to put my finger on it until I opened up my undergraduate biology textbook to prepare for a nature walk with my son’s 2nd grade class. I saw an intriguing diagram of the relationship between autotrophs and heterotrophs. An autotroph is any organism that makes its own food, e.g. plants through photosynthesis. Heterotrophs are organisms that cannot do this, which means every animal on the planet has to hunt for food, either by eating the autotrophs or by killing and then eating those who eat autotrophs. Obviously, we are heterotrophs, but we have brains that have adapted a conscience, which means we can see the purity of making our own food and conversely see the pain that killing causes. I believe that some people have a romantic desire for a “pure” diet that appeases their conscience.   

Meat is Good

At the other extreme is the “meat is good” argument, which is based on evidence that our early hominid ancestors began eating meat more than a million years ago and that, from an evolutionary perspective, our bodies have had time to adapt to a diet of meat. In contrast, humans have only been cultivating the land for grains and veggies for the last 11,000 years, which some argue is not enough time for our bodies to have adapted. Thus, it becomes highly unlikely that meat is the cause of our suddenly expanding waistlines. Some archaeologists believe that the adaptation to meat aided in our brains becoming larger.

Bolstering this argument is the fact that many primitive peoples, such as the Hadza and Inuit, have survived on diets of almost pure meat, and they rarely were afflicted with any of the chronic diseases associated with obesity until coming in contact with westernized foods such as refined carbs and sugar. Gary Taubes, author of Good Calories, Bad Calories (GCBC), brilliantly argues that dietary fat is wrongly accused as the culprit in heart disease and points the finger at sugar as the real killer. Taubes’s argument is very convincing. He is backed up by some of the most respected researchers in the field of nutrition who have published papers on taxing and regulating sugar, especially sugar sweetened beverages. Certainly from an evolutionary perspective, for many primitive societies, sugar was a seasonal delicacy and thus its consumption was regulated by nature. That sugar—particularly in drinks like syrupy lattes, white flour, and fried foods—is bad for you is not a contentious issue.

The flaws in the “meat is good” argument lie mostly in the extremes of their position. Look at the way Atkins demands stopping all carbs, at least temporarily, and the diet has produced a processed protein snack market. And although Taubes quietly acknowledges that there are good carbs and bad, his questioning of assumptions that fruit is healthy because no one has ever done a random controlled trial testing its efficacy distracts from his main message and leads people to dismiss his entire argument. Taubes is committed to his position and even posts his diet (bacon, sausage, burgers, and steak daily) and his triglyceride levels on his blog, but the fact that he enlisted a psychiatrist friend to order the tests strikes me as kind of weird.

Then there are the Paleo Diet people who really get into the purity aspect of man the hunter, the meat consumer. To me this position borders on Paleolithic fantasy, with romantic images of man the pure hunter carnivore. Although the idea that our bodies are adapted to eating meat is a valid argument, this camp just takes it to a level of impracticality so glaringly obvious that it’s hard to believe how zealous Paleo people can be. Humans have been genetically modifying food, wild or domestic, since we learned how to control our environment through selection and domestication. So it is impossible to find a truly sustainable Paleo diet on this planet. In addition, there is an unrealistic assumption that there was a homogenized caveman diet. Some Pleistocene era people lived near coasts and some in woodlands. Carbs and grains were certainly available. So again, I see this dietary choice as grasping for an unattainable purity on the other extreme.

Made for TV Confusion and Chaos

I could see people from both sides literally duking it out on the Discovery Channel. It might make for good television when science gets mixed in with zealots fighting over their extreme position, but I am tired of dietary purity and fantasy and I just want the facts. I just want to eat good tasting and healthy meals. So, to me the question really boils down to this: what would you do if suddenly you were diagnosed with coronary heart disease?

One reasonable voice can be found from the author, Richard Wrangham, who wrote the book Catching Fire: How Cooking Made Us Human. He makes a convincing case that cooking food maximized our caloric intake and thus freed humans to develop larger brains. Even Darwin said that cooking was humanity’s greatest discovery aside from language. The Paleo people are correct in that foods that are high in calories and low in nutrients (foods such as fast foods, candies, and frozen meals and that are abundant in obesogenic environments) are nowhere to be found on the African savanna. These are the kinds of foods that our bodies have not evolved to metabolize properly and, unfortunately, they are perfectly suited to our busy lifestyles. Meat is a whole food and it is something we have evolved to eat and digest. But that doesn’t mean eating a prime rib every night is great, and it doesn’t mean root veggies are going to make you fat.

Another way of looking at these extreme positions is seeing where they overlap. Consider a Venn diagram, with an overlapped area (below). This is where both arguments tend to agree on a whole-food diet and both also agree that highly processed foods are not healthy. So really the BIG disagreement is that at one extreme, eating meat is bad and at the other, it is good, with a whole spectrum in between. In this situation, I stick to the center, the overlapped area. Based on current available evidence, controversial as it is, I believe we need to stick to a traditional balanced diet that includes meats and lots of good carbs, such as whole grains, fruits, and veggies.

This validates the Italian-American food values I was raised with. My family believed in eating fresh, whole foods.  There wasn’t a focus on meat, but it was never demonized or romanticized either. I am now inspired to continue with that tradition of making well-balanced, home-cooked meals with fresh ingredients.  We all must find some common ground and admit that using less sugar and salt, very little white flour, limiting alcohol to a drink or two per day, and increasing veggie consumption are the safest bets for health. Personally, I’d stay away from extreme diets, like Atkins, Paleo, and veganism. Many of those diets have some research behind them, and they are not totally implausible, but they always seem to go out further that the evidence suggests. As the prominent scientist Medawar once said, “The intensity of the conviction that a hypothesis is true has no bearing on whether it is true or not.”

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