Sunday, August 07, 2011

Moving towards a whole foods, plant-based diet

I love to cook, and when I say cook, I mean I love Mario Batali and Anthony Bourdain meals, heavy on the meat, fat, and cheese. I never had much of a sweet tooth, but I certainly cannot deny that I crave animal fat. You could put a fresh, homemade chocolate cake in front of me, and not even a taste bud stirs, but make a juicy dish of braised shorts ribs and I become one of those kids in a Mischel experiment.

Recently, my brother and I got into a little argument. We never argue. During a banal phone conversation, he claimed that if everyone turned vegan, the world would be a better place. Being the one with a Master’s degree in health science, I disputed his claim. I threw out some facts, which mostly demonstrated my own bias against veganism.

A few weeks passed, during which time I stumbled across T. Colin Campbell’s book The China Study. The author tells the story of growing up on a dairy farm, drinking milk and eating meat every day, and then coming to the realization that animal-based foods cause cancer, heart disease, and a smorgasbord of chronic diseases.

Campbell was a respected researcher at MIT, and his early research on casein (milk protein) showed that it facilitated cancer tumor production or tumorogenesis in the livers of rats, while vegetable protein suppressed tumor production. He conducted an impressive range of studies on animal models demonstrating that dietary fat from animals, either in milk or meat, facilitated cancer more than leading carcinogens such as aflatoxin. This evidence led him to conduct one of the largest human nutrition epidemiological studies, in China.

This observational study compared lifestyle, dietary factors, and standard biological measures to investigate the amount of influence on all major chronic diseases across most of China, a country with a vast array of regional differences.

One of his major points is that only a small percentage of cancer development can be explained by genetics, while what we eat plays a much larger role, even more than known chemical carcinogenic exposures.

Important findings from the China Study:
1.     High dietary fat is positively associated with heart disease (by increasing bad cholesterol in the blood) 
2.     High animal protein consumption is positively associated with high cholesterol
3.     High animal protein consumption is positively associated with breast cancer
4.     Low animal protein consumption is associated with later menarche in women (through estrogen)
5.     Later menarche is strongly protective against breast cancer
6.     Late menopause is associated with higher breast cancer
7.     Animal protein consumption extends exposure to estrogen because it initiates early menarche and later menopause
8.     Animal protein is associated with many other chronic diseases as well.

If you Google “critiques of the China Study,” you will find some solid, honest criticisms. There is no question that there are some flaws in the study. However, what large-scale, cross-cultural study doesn’t have issues? I myself worked on one in India, and I can say this is a difficult type of study to pull off without flaws. Some of the critiques I read say that Campbell is biased towards a plant-based diet and only looks at studies that confirm his perspective. I think this criticism is off-target. Campbell may very well be biased, but he is totally transparent on every level. There are no hidden deals with the fruit and veggie oligopoly, unlike the meat and dairy industries’ backing of research favorable to them.

Others say he extrapolates too much from his research, and I agree with this to a point. My biggest issues with Campbell's argument are these:
1.     China in the 1980’s had many differences with westernized nations, going well beyond diet alone.
2.     He does an excellent job explaining the pathogeneses of some cancers and casein but I am not clear on other cancers.
3.     World cancer stats from 2002 show India with less incidence, prevalence, and mortality than China. This could be explained by China’s increase in animal protein consumption due to increases in incomes, but incomes in India have risen as well. (Although most Indians are vegetarian, they consume high amounts of milk, cheese, yogurt, and other animal-source foods.) More on this below.
4.     Comparing rural population health to urban population health is problematic.
5.     Western-based questionnaires, although translated, are challenging in a different cultural context. For example, people in China could define some food items differently than people in the US.

Even though I feel there are some over generalizations, the author is very clear about the weaknesses of study designs and provides a breadth of evidence, including randomized trials involving diet. The fact that the author provides so many peer-reviewed studies is a strong aspect of the book.

His advice uses a precautionary principled approach. He notes that one should do some research on plant-based proteins and a few essential nutrients that plants do not provide.  He also points out that diet has a huge effect on one’s metabolism and that in turn affects one’s physical activity. So he is not saying, as some criticize, that all you need to do is change your diet. He says that it is the biggest factor to change and also points out that moderate exercise is necessary.

Another strength of the book is that Campbell provides detailed explanations of why other competing dietary theories miss the mark. More often than not, popular diets do not provide any evidence to check the claims they make. This book’s credibility lies in how Campbell frames his argument using a Hill’s criteria-type of evidence evaluation, which lays out all the mechanisms of actions and pathways, discussing and citing research other than his own, thus adding consistency, coherence, and plausibility to his argument. He doesn’t just present one argument or one pathway like so many dietary theories. Another fact that adds credibility to Campbell’s argument is that the American Cancer Society added their own dietary recommendations, while less stringent about animal-based protein, they recommend increasing vegetable consumption. This is intriguing because the author discusses that they were previously opposed to Campbell’s position regarding any association between diet and cancer. Clearly, Campbell is a pioneer in this area.

His dietary recommendations might be even more extreme than evidence dictates, but as he repeatedly advocates a more safe-than-sorry approach. This is where I feel he is especially refreshing in an area like health and nutrition, where industry has infiltrated every nook and cranny to propagate its agenda, from government agencies to universities. There is so much conflicting information that no one actually knows how much animal protein is too much. So it seems prudent to err on the side of consuming a lot less than the more generous recommendations allow.

Perhaps the biggest question lingering for me is that I would like to see Campbell address India in his analysis. During my own research in India, I conducted a 200-person survey of western fast food eating habits. India is a fascinating case because it is a country of vegetarians, but the disease that claims the most lives is cardiovascular disease (CVD).

For India’s Hindu majority cows are sacred, which changes diets in two ways:  a taboo against killing cows means little beef is consumed, and milk is considered a divine gift so it is consumed whole and is incorporated into many dishes. My longstanding criticism of vegetarianism applies here. Just because someone is vegetarian doesn’t necessarily mean that they eat “healthier.” Lots of junk food is technically vegetarian, and many vegetarians substitute high consumption of dairy products for meat.

Using Campbell’s argument, high dairy consumption could explain high CVD mortality in India. But I am not sure how cancer fits in. I will have to research cancer rates, but I do know that diary consumption in India is at least equal, if not significantly more, than in China. So I am curious if Campbell’s theory of casein as a cause for cancer addresses this inconsistency.

While there may be leaps in some of Campbell’s claims, I have no doubt that diet plays a huge role in health and disease. The associations he has compiled are truly impressive. Equally impressive is the fact that he is not trying to sell his own cookbook or proprietary food system. He lays out very simple, clear guidelines for people to follow to change their diet. It is not some 3-week crash diet but is nothing short of a paradigm shift of typical eating habits.

After reading The China Study, I am definitely decreasing my consumption of animal-based protein (and my family’s, since I do most of the cooking). It will be a slow and demanding process, but the evidence seems clear. Tonight: roasted zucchini, pan-roasted turnips with poppy seeds, and radicchio pancakes. Bon appetite!

Stay tuned for more updates on my dietary paradigm shift, as well as commentaries on the counter position that we owe our great gains in human evolution to a meat-based diet. That claim is important in the Paleo-Diet, the Atkins Diet, and Gary Taubes’s interesting book Good Calories, Bad Calories, which I’m reading now.