Empirical Evidence: Greater Weight Loss And Fat Loss On Isocaloric High Protein Diets
Dozens of studies have demonstrated that high-protein diets result in greater loss of bodyweight and fat mass than isocaloric lower-protein diets. (Isocaloric = containing the same number of “calories”.)
Instead of bombarding you with citations, I’ll point you to references 11 through 44 (and 2) of this excellent paper:
Nutr Metab (Lond). 2012 Sep 12;9(1):81. doi: 10.1186/1743-7075-9-81.
Dietary protein in weight management: a review proposing protein spread and change theories.
Bosse JD, Dixon BM.
(Fulltext available here.)
While some will critique that the satiating effect of higher dietary protein sometimes results in voluntary hypophagia , leading to an energy intake discrepancy between groups, there is evidence that increased dietary protein leads to improved body composition and anthropometrics under iso-, hypo-, and hyper-caloric conditions [2, 11-44]. Thus, the traditional dogma of “energy in versus energy out” explaining weight and body compositional change is not entirely accurate.
Now, it’s quite possible to pick a fight by cherry-Googling a few studies that show no advantage to high-protein diets. CITATION WAR!!11!!!1 Who’s right?
Rule Of Thumb: When there is a wide spread of outcomes, it’s likely that other factors, besides the one being studied, are influencing the results.
For instance, there are studies showing that calcium supplementation increases weight loss, and studies showing it does not. Instead of arguing that the studies opposing one’s hypothesis must all be flawed or fabricated, it’s more productive to look for other factors…
…and indeed, we find that calcium supplementation only increases weight loss if one is calcium-deficient to begin with.
Br J Nutr. 2009 Mar;101(5):659-63.
Calcium plus vitamin D supplementation and fat mass loss in female very low-calcium consumers: potential link with a calcium-specific appetite control.
Major GC, Alarie FP, Doré J, Tremblay A.
The application to such controversies as “Is there a metabolic advantage to low-carb diets?” should be obvious.
First, we know that a host of factors besides protein intake influence weight and fat mass (some of which I discussed in Part II and Part III). Furthermore, the dozens of studies in question prescribed a wide range of diets—anything from nutrient shakes to nuts to protein supplements to prepared meals to “we give you dietary advice; you keep dietary records and we’ll analyze them for compliance”—so we would rightly expect some of these changes to influence study outcomes. Unfortunately, it’s difficult to discern patterns across such a wide range of variables.
However, Bosse and Dixon have found two factors that can easily be compared between studies: protein spread and protein change.
Protein spread is the difference in protein content between low- and high-protein diets; protein change is the difference in protein content between a test subject’s habitual diet and the high-protein diet.
“In studies where a higher protein intervention was deemed successful there was, on average, a 58.4% g/kg/day between group protein intake spread versus a 38.8% g/kg/day spread in studies where a higher protein diet was no more effective than control. The average change in habitual protein intake in studies showing higher protein to be more effective than control was +28.6% compared to +4.9% when additional protein was no more effective than control. Providing a sufficient deviation from habitual intake [“protein change” -JS] appears to be an important factor in determining the success of additional protein in weight management interventions.” (Ibid.)
Even more striking, when the authors excluded studies in which the protein content of the low-protein diet was insufficient to meet the RDA, the mean difference in spread increased from 19.6% to 21.7%, and the mean difference in change increased from 23.7% to 37%!
For those skeptical about the ranges in the above graphs: “…There appeared to be plausible explanations for nearly all outliers.” (Ibid.) Read the Discussion section if you’re interested in the details.
For instance: “A flaw in previous trials was that at times higher protein groups consumed more protein than control, yet less than their habitual intake, and saw no difference in anthropometrics [33, 52, 57, 61]. Thus, the “intervention” diet was really not an intervention to their metabolism. […] In some cases, increasing the % of kcals from protein during energy restriction can actually result in less protein being consumed during intervention than habitual intake as a simple function of energy deficit.” (Ibid.)
For example, if you design a 1000-“calorie” diet for someone whose habitual intake is 1900 “calories” with 15% protein, you’ll have to include 28.5% protein just to give them the same amount of protein they were getting before.
“What is the protein spread on this study?” and “What is the protein change in this study?” are common-sense questions to ask. If protein spread is too small, the diets will be too similar to cause significantly different outcomes. If protein change is too small, the “high-protein” diet won’t be different enough from a subject’s habitual diet to cause a significantly different outcome. So while other factors are very likely to influence the outcome, it’s clear that protein change (and, to a lesser extent, protein spread) account for most of the difference between outcomes in high-protein dietary interventions.
Conclusion: A calorie is not a calorie when you consume it as protein instead of fat or carbohydrate.
Our Story So Far
- A calorie is not a calorie when you eat it at a different time of day.
- A calorie is not a calorie when you eat it in a differently processed form.
- A calorie is not a calorie when you eat it as a wholly different food.
- A calorie is not a calorie when you eat it as protein, instead of carbohydrate or fat.
- Controlled weight-loss studies do not produce results consistent with “calorie math”.
- Calorie math doesn’t work for weight gain or weight loss.
What happens if we decide to “count calories” anyway? Continue to Part V, “Can You Really Count Calories?”.
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