Monday, February 6, 2012

High Carb vs. High Fat for Obese Type II Diabetics and What Really Happens, When Science Meets Real Life

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.
Today's SuppVersity post fits in nicely with the latest installment of the Intermittent Thoughts from yesterday and the post on the "heart-healthy low fat diet" from Friday, as it is about one of the few large(r) scale, long(er) term human trials on the effects of diets with different macronutrient-ratios in insulin-resistant human beings. As you would expect from an expensive nationally funded trial, a "high fat" diet (in the actual sense, not like the SAD diet from Friday) was not part of the study design and that despite the fact that not the US, but the New Zealand Health Research Council was the official financier of the multicentre (meaning that it was a corporation of several institutions) parallel design, blinded randomised control trial, the results of which have been published in the latest installment of Diabetologia (Krebs. 2011).

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)
In this regard, a brief glance at figure 1 should suffice to see that those "adherence" effects were in fact huge. The -500kcal reduction in energy intake was not achieved by either of the groups and the difference between the protein and the carbohydrate groups is more than significant. While the the average reduction in calorie intake in the protein group was ~146kcal/day and thusly <30% of the target, the high carb group with an average of ~238kcal/day did at least get close to the 50% mark... and as you may already have suspectes, things get even worse, when we take a look at the macronutrient ratios.

"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)
As the data in figure 2 goes our first prediction is true, but the adherence to the high protein intake declines and at the end of the study, the "high protein" group consumes hardly more protein than the "high carb" group (only 12 out of 206 subjects, i.e. 6%, achieved the prescribed 30% of total energy from protein goal!). Our second prediction, on the other hand, does not apply for either of the study periods, because even at the end of the study, the difference in carb intake between the "high protein" and the "high carb" groups is hardly significant.

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)
Fortunately, this is yet another instance, where the conventionally dietary wisdom with its adherence to the faulty calories-in-vs-calories-out paradigm and the notion that eating fat will make you fat, utterly fails:
  1. 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
  2. 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.
If we also take into consideration that the weight loss of the "high protein" group totally stalled as their compliance to the macronutrient intake plummeted from month 6 to month 12, the scientists conclusion that their study would show that ...
[...] 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 diet
maybe 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 ;-)