|Image 1: "You told me to eat more protein and this burger has both meat and cheese!" - This and other mishaps are among the reasons why calories still count in the books of most dietitians.|
What turns obese diabetics into bigger losers - high protein or high carb diets?
To test the hypothesis that weight and glucose management would be effected by the protein or carbohydrate content of the diet, the 419 obese, diabetic participants (age: 30-76, mean = 58y; BMI ~36.5kg/m²) were randomly assigned to one out of two dietary regimen, both of which aimed at a reduction of total calorie intake by ~500kcal/day. As far as the actual diets were concerned, the subjects were free to make their own choices based on portion charts, "culturally appropriate recipes" and what they had learned during an initial one-to-one discussions and the first group session.
What we are dealing here, is thusly basically the "free living individual" who tries his / her best to finally get rid of the weight by a reduction in total calorie intake. And while the latter may compromise the significance of the study results as a basis to speculate about complex underlying physiological responses to macronutrient manipulations, the 2-year study period with after all ~70% of the subjects making it to the 24-month visit at the end of the study, as well as the "I was sick of eating so much protein!"- and the "But I thought Twinkies and Dingdongs were high protein foods!"-factor provide a real-world significance neither of the controlled <30days lab experiments has.
|Figure 1: Actual reduction in energy intake (vs. baseline) in high protein and high carbohydrate group in the different stages of the trial (data calculated based on Krebs. 2011)|
"High protein diet" means that I just eat some additional protein, right?
Since ours, as well as the scientists' primary interest is in the differences between the macronutrient composition of the diets of the groups (and obviously their respective effects on weight loss and glucose management), I decided to plot the relative differences in total macronutrient intake between the groups, to make it easier to see how big the differences really were. Now, before you take a look at the data in figure 2 let's briefly discuss, what we should see there, when we plot the ratio of say protein(protein group) to protein(carbohydrate group)? Right, that should be way more than 1 or 100%. And the same for carbs? Right, that should be way less than 1 or 100%!
|Figure 2: Relative energy and macronutrient intake expressed as the ratio of total intake (kcal or g) in "high protein" to total intake in "high carbohydrate" group (data calculated based on Krebs. 2011)|
More fat, more protein, more energy, about the same amount of calories = ?
Now, given the fact that the obese diabetics in the "high protein" group obviously interpreted their diet as the "just eat more damn protein"-diet and thusly ended up consuming overall more energy from a higher protein and fat intake at about equal carbohydrate intakes, what does convential dietary wisdom tell us? Yeah, those gluttonous bastards should not lose a pound... I mean, come on -146kcal and all that fat?
|Figure 3: Weight loss and reduction in waist circumference expressed relative to reduction in energy intake (vs. baseline) during the individual phases of the dietary intervention and for the whole study period (data calculated based on Krebs. 2011)|
- The participants in the "high protein group" lost weight (-3.9kg vs. -6kg in the "high carb group), although they fell >70% short of the kcal-target of -500kcal/day
- On a "per-kcal-energy-reduction"-base (energy expressed relative to baseline; cf. figure 3), the participants in the "high protein" trial lost on average 13.1% more body weight and 14.5% more waist circumference, than their peers on the "high carbohydrate" diet.
[...] a high-protein diet with a group-based dietician-led support and education programme easily deliverable in a real-world setting does not promote greater weight loss than the prescription of a high-carbohydrate dietmaybe true (as the total differences were statistically non-significant), the underlying reason, is however the real-world setting and not, as a cursory read of the abstract would suggest, a consequence of the fact that macronutrient modulations would not effect weight loss. The latter in turn, should remind you why you originally came here today: For a discussion of recent scientific data that goes beyond what you will find on PubMed or in the 2nd hand-information the lay-press is cooking up from press-releases ;-)