Introduction
Recently, Jimmy Moore at Livin' La Vida Low-Carb linked to an epidemiological Greek Study that purported to compare mortality rates of Low-Carb/High-Protein and High-Carb/Low-Protein diets, along with a challenge from Dr. Steven Acocella - a vocal critic of low-carb diets - to refute it under the assumption that it is a legitimate study:
I will not editorialize on the study, but simply listen to you and your reader’s comments. I will say that there's no reason that we need to dispute the efficacy of the study itself. Let's go from the position that the study is not flawed. Let's discuss the science and findings.
The conclusions of the authors are reproducible and consistent. What do you all think? If you do post this study I applaud your willingness to explore the science and not ignore nor dismiss it.
Many of Jimmy's readers have been up to the challenge, and I would like to throw in my two-cents' worth.
First, let's examine the abstract, to get a basic understanding of the study. Here is the study objective:
We have evaluated the effects on mortality of habitual low carbohydrate–high-protein diets that are thought to contribute to weight control.
As the objective states, the object of the study was to evaluate the effect on mortality rate of so-called low-carbohydrate/high-protein diets - ostensibly, low-carbohydrate weight-loss diets.
The study setting is the general Greek population. Here are the subject methods:
Follow-up was performed from 1993 to 2003 in the context of the Greek component of the European Prospective Investigation into Cancer and nutrition. Participants were 22 944 healthy adults, whose diet was assessed through a validated questionnaire. Participants were distributed by increasing deciles according to protein intake or carbohydrate intake, as well as by an additive score generated by increasing decile intake of protein and decreasing decile intake of carbohydrates. Proportional hazards regression was used to assess the relation between high protein, high carbohydrate and the low carbohydrate–high protein score on the one hand and mortality on the other.
In other words, this is an epidemiological study based on the Greek-population subset (about 23,000 people) of the EPIC study from 1992 to 2003. Analysis is based on separating this subset into various decile groups based on descending protein intake, ascending carbohydrate intake, and a sum of the two deciles.
Understanding these groupings is key to understanding the study, so let's take some time with the explanation. For the three analysis groups, participants were separated into decile groups - that is, groups of 1/10 of the total - based on the given criterion. So, for the descending protein intake group, all 23,000 participants are ordered based on protein intake, and the highest 2,300 participants are placed in the first decile (and so on, for all 23,000 participants). Likewise for descending carbohydrate intake (except, in this case, the 2,300 lowest carbohydrate-intake participants are placed in the first decile). Finally, for the third analysis group, each participant's two decile "scores" (the first decile is scored a "1" and the tenth decile is scored a "10") are added together, and groups are defined from a "score" of 2 (low-carb/high-protein) to 20 (high-carb/low-protein). Make sense?
Moving on: The study claims the following results:
During 113 230 persons years of follow-up, there were 455 deaths. In models with energy adjustment, higher intake of carbohydrates was associated with significant reduction of total mortality, whereas higher intake of protein was associated with nonsignificant increase of total mortality (per decile, mortality ratios 0.94 with 95% CI 0.89 –0.99, and 1.02 with 95% CI 0.98 –1.07 respectively). Even more predictive of higher mortality were high values of the additive low carbohydrate–high protein score (per 5 units, mortality ratio 1.22 with 95% CI 1.09 –to 1.36). Positive associations of this score were noted with respect to both cardiovascular and cancer mortality.
Finally, the study makes the following conclusion:
Prolonged consumption of diets low in carbohydrates and high in protein is associated with an increase in total mortality.
Sounds pretty bad for low-carb diets, eh? Perhaps - or perhaps not. We need to dig deeper into the study in order to decide.
Read on, in Part 1: Is It Really Low-Carb?
