Zone Out

Neil Mann belongs to the team of researchers who work with Loren Cordain and promote high intakes of lean meat on an evolutionary basis.

For example, he authored Dietary lean red meat and human evolution in which he argues that various lines of study "indicate the reliance on meat intake as a major energy source by pre-agricultural humans."

Mann and another team from Royal Melbourne Institute of Technology published a new study of the efficacy of a high (30%) protein diet, in comparison to a high (55%) carbohydrate diet, for type 2 diabetes.

The effect of high-protein, low-carbohydrate diets in the treatment of type 2 diabetes: a 12 month randomised controlled trial.

In this study, 99 subjects received advice to follow low-fat (30% total energy) diets; 53 of those received instructions to eat a diet supplying 30% of total energy from protein and 40% from carbohydrate (high protein arm), while  46 received instructions to eat a diet supplying 55% of total energy from carbohydrate and 15% from protein.   

The high-protein diet had the same proportions of protein, fat, and carbohydrate (30:30:40) recommended by Barry Sears in his "Zone" diet books.  Supposedly this proportion produces better blood sugar and insulin control than a high carbohydrate, lower protein diet.

The aim was to find out if eating a diet high in protein would provide superior glycemic control to a diet high in carbohydrate, so the primary endpoint was change in HbA(1c).  "Secondary endpoints included changes in weight, lipids, blood pressure, renal function and calcium loss."

The results?

"HbA(1c) decreased in both groups over time, with no significant difference between groups (mean difference of the change at 12 months; 0.04 [95% CI -0.37, 0.46]; p = 0.44). Both groups also demonstrated decreases over time in weight, serum triacylglycerol and total cholesterol, and increases in HDL-cholesterol. No differences in blood pressure, renal function or calcium loss were seen."

Mann et al concluded:

"These results suggest that there is no superior long-term metabolic benefit of a high-protein diet over a high-carbohydrate in the management of type 2 diabetes."

I don't have access to the full text, but since the team that did this study includes Neil Mann, one of the strongest proponents of the idea that humans are adapted to diets high in animal protein, who might have a bias in favor of high-protein diets, this study appears to undermine the high-protein approach to diabetes.

It doesn't appear to do the Zone Diet any favors either. 

On the other hand, it supports the already established body of literature showing efficacy of a high-carbohydrate approach to diabetes type 2.   The high-carbohydrate diet apparently produced meaningful decreases in weight, HbA(1c), triglycerides, and total cholesterol, and increases in HDL.

The decrease in trigs and elevation of HDL are particularly of interest, since very often I see claims that high carb diets raise trigs and lower HDL. 


This study provides evidence against the claim that humans are specially, evolutionarily adapted to high-protein diets and maladapted to high-carbohydrate diets, and undermines the claim that this one disease of civilization, type 2 diabetes, and its chief feature, hyperinsulinemia, arise from high-carbohydrate diets. 

Of interest, both diets had relatively low fat contents.  Since altering the ratio of protein and carbohydrate appeared to have no effect on results, this study may also suggest that reduction of dietary fat proportion plays a key role in the treatment of type 2 diabetes if the goals are reduction of body mass, HbA(1c), triglycerides, and total cholesterol, along with increases of HDL.