Roger Zoul wrote:

First, the "primary analyses" of McManus et al were conducted using a
"low-fat" group in which 67% (20 of 30) subjects analyzed had dropped out of
the program. (6) Thus, they almost certainly were no longer following the
low-fat approach when they were counted as "low-fat" dieters. This group was
compared with a higher-fat group comprising 25 active participants and only
6 dropouts. Forty additional dropouts were not "available for measurements."
Based purely on research showing the powerful impact of active participation
in weight-loss programs, 67% of the low-fat group included in the primary
analyses would be expected to fare poorly, compared with 19% of the low-carb
group. (13) This differential subject attrition, one of the primary threats
to internal validity, was statistically very significant (P .001) but
ignored by the authors. When the researchers compared only current
participants (excluding dropouts), the groups did not differ in weight loss.

...

The
McManus and Yancy low-fat participants prematurely discontinued treatment
almost twice as often (43%) as their low-carbohydrate groups (24%). Unlike
McManus et al, however, Yancy et al did not analyze the data separately for
completers only. Without taking into account the likely poorer performance
of the greater number of dropouts in the low-fat group, Yancy et al may have
inadvertently skewed the results in favor of their low-carbohydrate group.

I agree that the low-carb study authors shouldn't have ignored
differential attrition, but on the other hand, if twice as many
subjects can't even stick to a 'moderate-fat' program, how do the
authors of this paper think they're all going to stick to a very low
fat program? Isn't the ability of people to maintain a way of eating
somewhat relevant? I totally believe that if you locked me in a room
and fed me nothing but white rice, I'd lose weight on a high-carb diet.
The thing is, I'm not locked in a room with nothing but rice, I'm out
in the real world, and whatever dietary manipulations I use to maintain
a healthy weight have to be something I can actually do in that
environment.

That's really my peeve with low-fat low-calorie dieting - I can
definitely lose weight on it, I'm just miserable the entire time. I
lost weight that way at one point, quite a bit, through iron willpower
and the constant support of a friend. God, I remember the stuff I ate
- all those salads with weird-tasting low-fat dressing, baked corn
chips with low-fat cheese, Snackwells cookies.... oh yick. And I was
*always* hungry.

Beth