I'm not convinced though. :-)

Yes, there's a lot of stuff in his editorial that is unstated, but there's some science to back it up. For example:

The trial by Sacks et al. lasted longer than most, the dropout rate was low, treatment was intensive, and compliance was assessed with objective biomarkers. 1 Unfortunately, the dietary goals were only partly achieved. Protein intake was intended to differ by 10% of energy between the high-protein-diet group and the average-protein-diet group, but the actual difference, as assessed by the measurement of urinary nitrogen excretion, was 1 to 2% of energy (according to my calculations, which were based on a diet that provided 1700 kcal per day). Extreme carbohydrate intakes also proved hard to achieve. When fat is replaced isocalorically by carbohydrate, high-density lipo-protein (HDL) cholesterol decreases in a predictable fashion. 3 The authors used the difference in the change in HDL cholesterol levels between the lowest- and highest-carbohydrate groups to calculate the difference in carbohydrate content between those diets. That difference turned out to be 6% of energy instead of the planned 30%.

As I read that, he's saying that the differences in the diets, as measured by chemical markers rather than reported intake, were too small to see if the diet was changed as intended.

Now maybe there are some problems with the calculations, maybe. I dunno. See the Sachs paper for more details. (Linky below.)

He strikes me as saying things very close to what you're saying. We all know there are diets that hardly have any meat or fat (pre-industrial China, India, etc.), and there are diets that hardly have any carbs or vegetables (Inuits, maybe some Pacific islanders that live on fish), etc. I think that's what he's referring to when he says that (roughly) "weight gain does not depend on the kind of calories". Obesity isn't common in most of those pre-industrial communities, so it can't be the type of calories that is the only thing that matters. And we all know there are problems with diet studies because, as he explicitly says, it's impossible for them to be "double-blind", among other things.

But it's also the case, based on what happens in most people like those in the study (average age early 50s, average BMI 33, 33% having hypertension, etc.), that eating saturated fats raises LDL. Does it happen to everyone? Of course not. We all agree that many, many things go on in the body that aren't terribly well understood. And t seems likely to me that the effect of diet changes as we age. (E.g. drugs metabolize differently in the elderly, why wouldn't food?)

Also, remember the Editorial is mainly a bit of background and an introduction to Sacks' paper. That paper is here - http://www.seriecientifica.org/sites/default/files/sacksfmetal_-_comparison_of_weight-loss_diets_with_different_compositions_0.pdf (15 page .PDF). It's been cited 849 times - a monstrous number. (That indicates people in the field think it is important, but not necessarily the last word of course.)

My $0.02, FWIW. :-)

Cheers,
Scott.
(Who is interested to see how his blood results will have changed at his next checkup (in a few months).)