Yet though the tides may be turning ...
... a paradigm shift within the scientific community usually doesn't come over night - a famous scientist and philosopher of science once said that it usually takes until the proponents of the old paradigm died out, before a new one is fully established. Since roughly two years and even two decades are hardly enough for this to happen, it is actually not surprising that Dawn. D. Campbell and Kelly A. Meckling, despite giving the high protein diet credit for having produced some promising results in the past, speculate that
"the combined effects of a normal protein: carbohydrate ratio with cardiovascular and resistance training would be more beneficial and easier to comply with than either the low- or high-protein diets in this target population of women with risk factors for the MetS" (Campbell. 2012)In view of the fact that Rehm et al. conclude ther 2008 review of the literature with the statement...
"Diets moderately increased in protein and modestly restricted in carbohydrate and fat, particularly saturated fat, may have beneficial effects on body weight, body composition, and associated metabolic parameters." (Rehm. 2008)... and against the background that the evidence of the real-world benefits of a higher protein intake is accumulating, and pertinent reviews and editorials have been appearing on a monthly basis, ever since (e.g. Hession. 2009; Keller. 2011; Acheson. 2012), the research hypothesis of the study at hand sounds a bit 'last year', not to say 'last decade' to me.
Do we have a bias here?
Moroever, with the research hypothesis being a good indicator of a built-in bias, we will have to pay pretty close attention to distinguish the actual data Campbell and Meckling measured from their interpretations of the latter. After all, every "good" SuppVersity student should remember that we have seen time and again how the differences between facts and interpretations often become somewhat blurry in the conclusions of way too many (for my liking) papers as of late. So let's see if Campbell's and Meckling's conclusion that...
"A diet with a 1:2 protein:carbohydrate ratio promoted better improvements than either the LP or HP diets, and may be superior in reducing long-term chronic disease risk in this population." (my emphasis in Campbell. 2012)What can be said right away is that the protocol the scientists used, specifically the way they are working with macronutrient ratios instead of paradigmatic percentages of the RDA, is actually pretty progressive.
"Subjects were encouraged to consume whole foods as opposed to pre-packaged or processed foods and to restrict intake of whole-fat dairy, high-fat red meats, deep-fried foods, potato chips, cookies and refined sugar products. Instead, subjects were encouraged to choose whole-grain pro-ducts, lower-fat meats, fish, turkey, eggs, low-fat milk and cot-tage cheese, nuts, seeds, and a variety of vegetables, fruits and berries. Before beginning the study workout programme, subjects completed baseline fitness testing to assess muscular strength and cardiovascular fitness." (Campbell. 2012)Instead of simply upping the protein intake from the 0.8g/kg body weight the RDA suggest would be optimal, Campbell and Meckling put their obese (mean BMI ~35kg/m²) female participants (of which only 54 completed the study) on calorically restricted diets (supposedly -30% below their habitual energy intake which had been evaluated by the means of a 7-day food record) which contained an equal relative amount of fat (<30%), but had different protein-to-carbohydrate ratios:
- low protein (LP) - 1g protein : 4g carbohydrates
- medium protein (MP) - 1g protein : 2g carbohydrates
- high protein (HP) - 1g protein : 1g carbohydrates
There is no effective weight loss without exercise and a whole food diet!
In addition to the dietary regimen the 117 participants who initially met the eligibility criteria were supposed to particpate in a supervised 12-week circuit training program at the University of Guelph Athletic Centre.
The 1 h study fitness programme was completed three times/week on Mondays, Wednesdays and Fridays at a consistent time assigned to each subject. Subjects had to sign in for their workout sessions, and all exercises were supervised by a study coordinator and/or personal trainer. Subjects began their workout with a 9 min warm-up using springboard pads where walking in place, jogging or dancing took place. Then, subjects completed a 30 min circuit alternat-ing between resistance training and cardiovascular exercise bouts. All main muscle groups of the body were targeted throughout the thirteen resistance training machines. Starting weight values on resistance training equipment were 65 % of their calculated maximum strength as determined by their modified 1 repetition maximum. Subjects were instructed to complete one set of eight to fifteen repetitions on each piece of equipment to reach muscle fatigue."The circuit training used a build-in progression with ~5% increases in weight, whenever the subject were able to complete 15 repetitions on a given exercise. The same goes for the aerobic parts of the workouts, where the
Subjects began exercising at 65 % of their maximum heart rate for the first 3 weeks and gradually increased the intensity by 5 % every 3 weeks to a maximum intensity of 80 % by week 12.As far as the aerobic part of the workouts was concerned, they alternated between a step, springboard pad and stationary bike. All workouts closed with some ab training (including a standard crunch, oblique crunch and a core-strengthening exercise called the plank, done to failure) and stretching.
"Hey, exercise is good for me!"
Other than you may have expected the 35 dropouts (which were equally distributed across all dietary groups) were not brought about by laziness or the unwillingness to get up and move. On the contrary, many subjects recorded that they had "more energy and felt better than before the study began" (Campbell. 2012). Aside from minor constipation (the scientists don't mention in which group this occured) and some minor shedding in one of the subjects in the low protein group (probably coincidence, by the way), the intervention went fine for those who had the guts, time and discipline to stick it and yielded - as the data in figure 1 goes to show - favorable results in all three arms off the study:
|Figure 1: Changes in antroprometric data, blood pressure and heart rate after 12 weeks (based on Campbell. 2012)|
"Again, the decrease in the NP group was greater than that in the LP group. Further-more, hip circumferences decreased similarly (P < 0·05) in response to each diet with reductions of 7·4, 8·8 and 8·4 cm in the LP, NP and HP groups, respectively. Waist:hip ratios declined significantly (P < 0·05) after 12 weeks by 0·01, 0·04 and 0·01 in the LP, NP and HP groups, respectively, but reductions were greater in the NP v. LP (P=0·020) and HP (P=0·025) groups." (Cambell. 2012)No group specific diet effects were observed for the reductions in blood pressure and heart rate. Now, this obviously raises the question, whether the existent changes may have been brought about by non-compliance.
"So maybe the protein eaters just didn't eat their protein?"
Non-compliance is, as SuppVersity students know, one of the major problems with all of these relatively uncontrolled dietary interventions (see "High Carb vs. High Fat: What Really Happens When Science Meets the Real World"). And in fact, with average caloric intakes of 3641, 3729 and 3633 kJ/d in in the low, medium and high protein groups, the subjects were actually consuming 10% less energy than they were supposed to.
|Suggested read for everyone who can't or doesn't want to believe that you can easily eat 157g of carbs (which is what the women in the normal protein group did) and still lose fat while retaining all your precious lean muscle mass: "Carbohydrate Shortage in Paleo Land: New Data for A Scientific Outlook at the Low-to-No Carb Paleo Confusion. Will More Than 125g of Carbs Make You Fat?" (read more)|
- significant decreases in protein intake (82 and 88 g/d to 55 and 75 g/d) for the low and normal protein groups and
- significant increases in protein intake (from 84 to 100 g/d) in the high protein group
The subjects in the normal protein intake group were about as close as you can get and those in the high protein group consumed significantly more protein than the 'well-meaning' authors of the dietary recommendations feel would be good for them ;-) Other changes the scientists observed were:
- a significant declines in carbohydrate intake in the normal and high protein group
- a decreased sugar intake in all groups (most pronounced in the HP group)
- a decreased fat intake in all groups (p<0.001)
- significant decreases in sodium intake in all groups
- non-significant decreases in calcium, zinc and vitamin D intake
So what?! Normal protein rules?
No matter how you look at the results of the study at hand, based solely on the data Campbell and Meckling presented here, there is not a single argument to brought forward in favor of the 1:1 vs. the 1:2 protein to carbohydrate ratio. Moreover, the single most important determinant of (long-term) dietary success that is the ease with which dieters feel they can adhere to a given nutritional protocol also speaks in favor of the normal, not the high protein diet. The answer to the initially raised question, whether the scientists' conclusion that..
"[a] diet with a 1:2 protein:carbohydrate ratio promoted better improvements than either the LP or HP diets, and may be superior in reducing long-term chronic disease risk in this population" (my emphasis in Campbell. 2012)...was biased by their own research hypothesis would therefore be "NO! It wasn't." - Now, that does not change the fact that I personally am biased and would therefore have liked the ladies to get past the 90g of quality protein / day margin. This would incidentally not have been difficult, if these wannabe overachievers had not reduced their caloric intake from ~2,300kcal/day to ~1,360kcal, but had contended themselves with the planned -30% reduction. The difference of 230kcal/day would left more than enough room for two additional protein shakes per day!
|Figure 2: Fat loss and lean mass gains of the police officers in the Demling study (Demling. 2000)|
It should be said, though that the 'success ratio' of carbs to protein in the Demling study was likewise ~1:2 (!) - the sole difference was that the obese police officers in the Demling study simply ate twice as much protein and twice as much carbs with a baseline fat intake of ~35g per day.
- Acheson KJ. Higher-protein diets for health? European Journal of Clinical Nutrition. 2012; 66, 763–764.
- Brehm BJ, D'Alessio DA. Benefits of high-protein weight loss diets: enough evidence for practice? Curr Opin Endocrinol Diabetes Obes. 2008 Oct;15(5):416-21.
- Campbell DD, Meckling KA. Effect of the protein:carbohydrate ratio in hypoenergetic diets on metabolic syndrome risk factors in exercising overweight and obese women. Br J Nutr. 2012 Nov;108(9):1658-71.
- Demling RH, DeSanti L. Effect of a hypocaloric diet, increased protein intake and resistance training on lean mass gains and fat mass loss in overweight police officers. Ann Nutr Metab. 2000;44(1):21-9.
- Hession M, Rolland C, Kulkarni U, Wise A, Broom J. Systematic review of randomized controlled trials of low-carbohydrate vs. low-fat/low-calorie diets in the management of obesity and its comorbidities. Obes Rev. 2009 Jan;10(1):36-50.
- Keller U. Dietary proteins in obesity and in diabetes. Int J Vitam Nutr Res. 2011 Mar;81(2-3):125-33.