Yesterday Dinneen told us how she used to follow all the latest “conventional wisdom” about how to eat. Until she went to France, and saw people enjoying real food, and enjoying much better health than we do in the U.S.
In the comments, MeadowLark posted a link to an article describing a study comparing four different types of diet. I’ve never taken an entire post to discuss health issues before, only noting them in passing. But this article got so many things wrong that I want to use it as an example of why I started writing this blog.
Faulty assumptions
Here’s the introduction to the article on CNN.com:
Researchers at the Harvard School of Public Health and the Pennington Biomedical Research Center put four popular diets — high carb, high fat, low-fat and high protein — to the test to see which of the regimens resulted in more weight-loss success.
After two years of monitoring the participants, “all the diets were winners,” said study co-author Dr. Frank Sacks, a professor of cardiovascular disease prevention at the Harvard School of Public Health. “All produced weight loss and improvements in lipids, reduction in insulin.
“The key really is that it’s calories. It’s not the content of fat or carbohydrates, it’s just calories,” said Sacks. The findings are published in the latest edition of the New England Journal of Medicine.
Let’s just start with the assumptions they clearly started from. Later in the article we see that the definition of “high fat” diet was one where 40% of all calories from from fat. In fact there was a study in 1960s performed by John Yudkin’s group at the University of London (get your copy here) where fat accounted for nearly 61% of calories consumed.
Leaving aside the results of the Yudkin study — which I’ll come back to — it’s clear that the recent Harvard study was really comparing low-fat to lower-fat diets. A genuinely high fat diet was never even considered.
Flawed methodology
If the goal is to compare different diets, you need some way to control what people are actually eating. But according to the CNN article:
Participants could attend individual sessions where dieticians educated them and group sessions where they discussed their experiences with one another.
Those who had better attendance in the sessions had stronger weight-loss results. “These findings together point to behavioral factors rather than macronutrient metabolism as the main influences on weight loss,” according to the study.
This suggests that study participants were assigned a diet to follow, but their compliance was a matter of individual effort.
Not only that, but diet subjects are notoriously bad at self-reporting what they ate.
This second excerpt from the study properly concludes that behavior was a better predictor of results than which of the diets a participant was assigned. A conclusion that the co-author completely contradicts in his summary, quoted in the beginning of the article. The part most likely to be read by most people.
At best, it seems, this study was unable to conclude anything about which diet was better.
Different agenda
Note who did the study: a professor of cardiovascular disease prevention. Weight loss was only one of several factors used to judge success of the diets: “All [diets] produced weight loss and improvements in lipids, reduction in insulin.” These three factors are believed by some researchers to affect heart health.
But the study didn’t actually measure cardiac outcomes. To conclude anything about heart health from this, you would have to accept the lipid hypothesis.
By the way, I realize I’m linking to a ton of extra reading here. But there’s a lot of research that suggests the last several decades of official recommendations have been wrong. There’s a lot more that I could be linking if I wanted to.
It all adds up to: just plain wrong
So if this study wasn’t really comparing high fat to low fat diets, if they didn’t control what people actually ate, if they weren’t even looking primarily for effects on weight, are there any other studies that didn’t have these flaws? As a matter of fact, there are.
The Yudkin study, which I mentioned earlier, placed people on a high fat diet — 61% of calorie intake — and found that people spontaneously limited themselves to less than 1600 calories per day. They felt full and lost weight.
And in 1944 Ancel Keys performed a starvation study, where subjects were placed on an extremely low fat diet — just over 17%. The total calorie intake in the two studies was nearly identical, but in the starvation diet people became emaciated, obsessed with food, and in several cases developed significant psychological problems.
There’s a really good analysis of these studies at The Four Hour Workweek in The Science of Fat-Loss: Why a Calorie Isn’t Always a Calorie.
If you find this conclusion a little hard to believe, think about this: One rice cake is about 35 calories. One cubic inch of beef jerky, three or four strips, is 49 calories. Which snack would satisfy your hunger longer, two rice cakes or a small bag of beef jerky? The rice might fill your belly, but you’ll still be hungry.
Enough crying wolf
Food scientists, politicians and food industry spokesmen have told us fat is bad, vegetable shortening is good, cholesterol is bad, carbs are good, carbs are bad, some cholesterol is good, vegetable shortening is bad, some fat is good … And this time they’re sure.
I haven’t seen any study that convincingly makes a conclusion about a single nutrient. I haven’t seen any study showing that a new diet is better for the general population than any of the traditional diets. Until I do, I’m going to keep eating beef, bacon fat, butter, whole milk … and fresh fruits and vegetables, home-made bread and pasta. And writing about it right here.
