Lately, a 2007 study has been circulating Facebook and the blogosphere, mostly being cited as support for a low-carb diet. Brainy Kris Gunnars reviewed it on his blog as a high-quality study showing that high-fat diets outperform vegetarian/vegan ones in terms of weight loss and cardiovascular risk markers.
After reading that, something twigged in my brain. I realised that we are talking about this study:
Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women.
I read it a while back and put it on my pile of studies that don't say much. I'm going to quickly critique the study now, as an example of how sometimes, what we think we see, is not what is there. You have to look beyond what you read on the internet or on Facebook. Don't trust anyone, especially bloggers ;).
The first, and most important issue, is compliance.
Leaving aside the fact that dietary compliance was assessed by telephone food recall, the A-Z study appears to have a serious problem with compliance to the diets, except Atkins. There are a couple of things that stand out to me.
The Zone Diet is supposed to be 40:30:30 (percentage of carbs, protein, fat) and yet, by the end of the study, the Zone dieters were achieving just 20%, and their protein intake had been dropping at each recall.
The Ornish diet is supposed to be very low fat (less than 10% of calories from fat) and yet by at the 12 month recall, the Ornish dieters were eating approximately 29.8% of their calories as fat. Surprisingly, these low-fat, vegetarian dieters somehow managed less than 20g of fibre a day. That's not even the RDI, which in NZ is 25g a day. This suggests to me that they were perhaps eating a few too many processed carbs instead of veges. Just a guess there. Therefore, although the Atkins group were Atkins-ing, the Ornish group weren't Ornish-ing and the Zoners were not in the Zone. The LEARN group didn't meet their dietary targets (55-60% calories from carbs, less than 10% calories from saturated fat) either.
So really, we are not comparing the results of the Atkins, LEARN, Zone and Ornish diets at all. This is major. Other studies like the POUNDSLOST trial have shown that dietary compliance matters more than nutritional breakdown when it comes to weight loss. I think the A-Z authors knew they had a problem there. A year later, some members of the original study group re-analysed the data for compliance and found this:
That messes with the notion that only the Atkins group lost lots of weight, although the most compliant of them did lose the most. It seems that the most compliant lost more than twice the previously reported amount on the Zone and nearly three times the previously reported amount on the Ornish diet. The LEARN diet was not included in the adherence analysis. The authors of the review concluded this (bolding is mine):
Regardless of assigned diet groups, 12-month weight change was greater in the most adherent compared to the least adherent tertiles. These results suggest that strategies to increase adherence may deserve more emphasis than the specific macronutrient composition of the weight loss diet itself in supporting successful weight loss.
Oh dear. That's interesting. I wonder why that follow up study isn't bounding around the interwebs? Probably because it's a predictable and boring finding. Nobody likes to cheer for the mainstream.
Let's have a closer look at the actual results from the original study.
Firstly, there is something important to realise from the get-go. Apart from the difference between Atkins and Zone Diet (which as mentioned above, was not really), the weight lost between groups was not statistically significant at 12 months. That means that given the group sizes, we can't be sure that the apparent difference in weights is not just chance.
There is also something weird going on with bodyfat levels. It's a bit of an elephant in the room, if you ask me. Have a look at this:
The readers of Fit to Blog are pretty smart and I'm sure you can see what's going on. In the last six months of the study, all groups except Ornish are regaining fat and increasing their BMI. The LEARN group regained the most bodyfat, with Atkins second.
I would dearly love to see a follow up study to see where these individuals (all women) are now. That would be truly interesting, yes? I wonder how they are doing seven years later?
Just a little note about the other significant findings, which were blood pressure, triglycerides and HDL. At 12 months, the Atkins group did show significant lowering of triglycerides compared to the Zone group, significant lowering of blood pressure compared to all groups and significant increases in HDL ('good' cholesterol) compared to Ornish. You can see this in the table above. The results with little a's and b's beside them are significant results, but numbers that share a superscript are not significantly different to each other (making sense??). I was a little 'meh' about these findings though, because the group as a whole had pretty good levels of these things at baseline, and of course, we still have the compliance issue.
In summary, it is really difficult to see how the Atkins foundation (it's even on their Wiki page), and other low-carb fans, can take this study and use it to smack the internet with the healthfulness of their diet. I'll need to see something a whole lot more convincing than this before erecting an altar to Atkins in my office.