Saturday, September 20, 2014

Does Dean Ornish know how to Google? More on the science of low-carb diets

You've probably heard about the latest study of low-carb diets. It's been covered by every major  media outlet in recent weeks. But in case you haven't heard, the study found that low-carb diets are better for weight loss and improving heart health than low-fat diets.

 It wasn't the first paper to find in favor of an Atkins-like diet and it won't be the last, but because of all the media attention it received, every weight loss guru has weighed in on the study, including Dr. Dean Ornish.

Ornish is a scientist, but it's probably more accurate to call him a vegan apologist, because he's never let the facts get in the way of defending his preferred diet. Though I'm not an expert, I have a functioning brain and access to Google, so it was awfully easy to poke holes in Ornish' review of the Tulane study. His criticisms are neatly arranged into a list, so I'll offer a few comments in the same format.

1. It’s not low carb vs. low fat. It’s both: an optimal diet is low in unhealthful carbs (both sugar and other refined carbohydrates) and low in fat (especially saturated fats and trans fats), as well as in red meat and processed foods.
No, it isn't. Even if a good diet can be low in fat, it's not correct to lump saturated fat together with trans fats and processed foods. We know that people who go on high-fat diets usually lose a lot of weight and see their metabolic health improve dramatically. Study after study after study tells us so. We also have evidence that trans fats and processed foods are unquestionably unhealthy. If you were to reduce your intake of carbs, trans fats and processed foods and up your saturated fat intake, as any good low-carb diet requires, you'd almost certainly lose weight.

2. This study did not distinguish between the types of carbs and fats. Patients in the “low-fat” group of the study increased their consumption of “bad carbs” (sugar and refined carbohydrates) during the study.
Indeed it did distinguish between good and bad carbs and fats. And as the New York Times pointed out, the low-fat diet was in line with the federal government's Dietary Reference Intake recommendations.

3. The “low-fat diet” in this study was not very low in fat. Participants in the “low-fat” group decreased from 35% fat to 30% fat over the course of the study, hardly any change at all. 
Fewer than half your daily calories from fat is a low-fat diet by anybody's standard, except for maybe Ornish'. He says his patients follow a plant-based diet as low as 10% in fat and fare much better than the low-fat group in the Tulane study did, but, I'll reiterate, people who drop the carbs and go on high-fat diets see similar results, and in some studies they even do better than people on the Ornish diet.

4. Perhaps most important, risk factors are not diseases; they are important only to the degree that they affect the underlying disease process. An article published in The New England Journal of Medicine showed what happens inside your arteries on different diets.
Yes, that's true, I guess. But if you can lose weight  and keep it off and you're not showing signs of developing heart disease, it's probably safe to say're not going to develop heart disease. But what of this study in the NEJM? Ornish says it shows that a low-carb diet can clog your arteries. What he doesn't say is that the study involved rats, and the chow they consumed was at best a rough substitute for a low-carb diet actual people would follow. Again, for the third time, we have clinical data showing how people do on low-carb diets. I'll leave it to you to figure out why Ornish cites an animal study instead of one the clinical trials I cited above.

I am not aware of a single study published in a peer-reviewed journal showing that a low-carb diet such as the one described in the Tulane study has stopped or reversed the progression of coronary heart disease. 
But we have research, the Tulane study included, showing that low-carb diets reduce risk factors for heart disease. We also have observational studies showing that people who consume more animal fat are less likely to die of heart disease. I wonder if the two are connected?

Ornish goes on to cite some of his own work showing the benefits of a very low-fat diet. I think he's overselling the benefits of his diet, but I don't fault anyone who wants to try it. Compared to the way most Americans eat, it's far healthier. Nonetheless, it's dishonest of Ornish to trash low-carb diets in the process. I'm forced to conclude that he is ignoring data that doesn't fit his narrative, or he doesn't have access to a search engine. I'm not sure which is more likely.

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