Saw Walter Willett speak today at the Boston Medical Center. Apparently Dr. Willett is one of the most frequently quoted scientists of all time, and widely respected in the field. He presented a quick history of the last few decades of nutrition research. There were some interesting points, but my overall impression was one of surprise at what a narrow view he presented on the issue. I suspect that's due not to any failing on his part, but on the nature of the field - it may really be that limited.
On a side note, big ups to Dr. Willett for riding his bike to the lecture despite the rain. Especially considering he was nicely dressed in a suit and not visibly wet.
What he said
Much of the 20th century: don't eat lots of fat
Worldwide studies in the 60s and 70s found strong correlations between eating saturated fat and animal meat and higher rates of cancer and heart disease. This led to the nutritional advice we're most familiar with: eat a low fat diet, minimize red meat. The classic food pyramid is partially a result of this. So are the sugary foods you can find everywhere, because they're low fat (even though our bodies are very good at turning sugar into fat as soon as we eat it).
Recently: not so simple?
Within the last 20 years, studies started showing that diets richer in olive oil were healthier than those rich in complex carbs. It became clear that not all fat was created equal: trans fats are highly correlated to heart disease, while mono- and poly-unsaturated fats have a slight negative correlation. Total fat intake turns out not to correlate to breast cancer rates.
This year, the Women's Health Initiative study suggested that overall percentage of fat in the diet doesn't have a measurable connection to heart disease or cancer. Whoops. Already there was significant doubt, thanks to some short-term successes with the Atkins and related diets.
Not everything nutritionists have told us is now thought to be wrong - for example, it's pretty clear that getting five servings a day of vegetables will reduce your chance of heart disease. It's also pretty clear that people can significantly reduce their chances of heart disease and cancer by:
- Keeping Body Mass Index under 25
- not smoking
- getting at least 30 minutes of moderate exercise (like brisk walking) a day
- eating a diet with whole grains and good fats
What I thought about what he said
The science of nutrition is pretty confused
Dr. Willett made this point pretty clearly, especially with regards to the Women's Health Initiative fat study. Here was a huge study, run by the country's best investigators, consuming on the order of $5 billion -- and it only served to further confuse things. Some of the problems with the study include participants not accurately reporting their diets, the design of the study making faulty assumptions about the role of overall fat intake vs. the different kinds of fats, and the sheer scale of the thing. So even for the limited aspects of the "what should we eat" question that nutrition tries to answer, things are murky.
What about the rest of the picture?
I can appreciate the advantage a program of scientific inquiry enjoys when focusing very tightly on a subject. Given that, I was struck by how little of the bigger picture of food systems was addressed by this presentation. The question "what should we eat?" is only partially answered by studying diseases in specific individuals; other significant considerations are society-wide food safety, economics, environmental issues, culture, and traditions. I don't know that a nutritionist would include these factors in a study, but to mostly ignore them from the sort of discussion we had today is weird and limiting. Again, I'm not blaming Dr. Willett; this seems like a systematic problem with nutrition.
A few things I was surprised not to hear about at all:
- the role of a food's freshness (local vs. shipped from NZ)
- pesticides, herbicides, and other industrial contaminants
- anything relating to environmental concerns
- food security
- malnutrition among the poor
What about traditional foodways?
Dr. Willett made a few brief mentions of specific food traditions, such as those found on the Greek island of Crete, and throughout the Mediterranean and Asia. Given that these traditions represent tens of thousands of years of trial and error, it's astounding to me that nutritionists don't pay closer attention. The stuff we eat in industrialized nations is highly affected by the priorities of the food industry, government subsidies, industrial pollution, and a host of other recent factors; why not establish some baselines by looking seriously at diets that are known to work under conditions closer to those that humans have lived under for much longer periods of time?
Update
I've received some feedback that my take on Dr. Willett's talk was pretty negative. My reaction was partially due to the expectations I carried into the talk. The title of the talk was The Search for Optimal Diets: A Progress Report, which led me to expect a more general overview of healthy food systems. Dr. Willett is also the author of a bestselling book titled Eat, Drink and Be Healthy: The Harvard Medical School Guide to Healthy Eating, so he's in the practice of giving advice to the public on these issues. I haven't read the book, so it may be that he covers a bigger part of the picture there. Similarly, there are probably nutritionists talking about all of the concerns I raised; I just haven't heard about them from the mainstream media, and I didn't hear about them from Dr. Willett in what seemed like an appropriate venue.[/food]
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