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What Nigh The Other Weight Loss Diet Study??

The same solar daytime the low-fat vs low-carb study past times Bazzano too colleagues was published, the Journal of the American Medical Association published a meta-analysis that compared the effectiveness of "named diet programs".  Many people own got interpreted this study every bit demonstrating that low-carbohydrate too low-fat diets are both effective for weight loss, too that nosotros only necessitate to selection a diet too stick amongst it, but that's non truly what the study showed.  Let's own got a closer look.

Johnston too colleagues sifted through PubMed for studies that evaluated "named diet programs", such every bit Ornish, Atkins, LEARN, Weight Watchers, etc (1).  In addition, the methods dry reason that they included whatsoever study every bit low-carbohydrate that recommended less than 40% of calories from carbohydrate, was funded past times the Atkins foundation, or was "Atkins-like".  These criteria weren't extended to the low-fat diet: exclusively studies of name-brand low-fat diets similar the Ornish diet were included, piece the meta-analysis excluded low-fat diet studies whose guidelines were based on recommendations from authorities too academic sources, fifty-fifty though the latter grouping represents the bulk of the show nosotros own got for low-fat diets.  The inclusion criteria were thence extremely asymmetrical inward how they represented low-carb too low-fat diets.  This fact explains the odd findings of the paper.

The abstract at nowadays activated my skeptic alarm, because it states that at the one-year mark, low-carbohydrate diets too low-fat diets both led to a sustained weight loss of virtually sixteen pounds (7.3 kg).  Based on my agreement of the weight loss literature, that issue seems far besides high for the low-fat diet, too also besides high for the low-carbohydrate diet.

OK, I thought, where's Shai?  Shai et al. was, inward my opinion, ane of the best multi-diet studies, amongst low-carb, low-fat, too Mediterranean diet arms (2).  Follow-up went out to 2 years, too compliance was fairly practiced for the entire time.  Johnston too colleagues did include Shai, but they exclusively included the low-carb arm!  The low-fat arm was excluded from the analysis presumably because it wasn't a "named diet program"; it was a calorie-restricted low-fat diet based on American Heart Association guidelines.  This arm lost virtually 8 lbs (3.6 kg) at the one-year mark, vs. unopen to 12 lbs (5.4 kg) for the low-carb arm.

How virtually Brehm et al. (2003)?  This 6-month study compared a low-carb to a low-fat diet, finding that low-carb led to greater weight loss of xix lbs (8.5 kg) vs. ix lbs (3.9 kg) for low-fat (3).  Again, exclusively the low-carb arm was included inward the meta-analysis; the low-fat arm was excluded presumably because it wasn't a "named diet program"; it was an anonymous calorie-restricted low-fat diet.

How virtually Samaha et al?  Again, the study included a low-carb too a low-fat arm, but exclusively the low-carb arm made it into the meta-analysis (4).  After vi months, the low-carb arm had lost thirteen lbs (5.7 kg) vs. exclusively four lbs (1.9 kg) inward the low-fat group.

What gain nosotros notice when nosotros facial expression at other meta-analyses of low-fat too low-carb diets that had to a greater extent than balanced inclusion criteria?  Hession et al. (2009) conducted a systematic meta-analysis of studies that compared low-carb to low-fat weight loss diets inward overweight too obese individuals (5).  This meta-analysis identified 7 studies that met inclusion criteria too had a follow-up catamenia of at to the lowest degree ane year.  Weight loss inward the low-carb arm ranged from 5-20 lbs (2-9 kg), amongst an average loss of eleven lbs (5 kg).  The low-fat arm also ranged from 5-20 lbs (2-9 kg), amongst an average loss of ix lbs (4 kg).  The low-carb diet led to significantly greater weight loss, but the departure was real small, too neither diet produced real impressive weight loss at ane year.  The departure inward weight loss betwixt diets was larger at vi months.

Another item that complicates interpretation of the Johnston meta-analysis is that many of the diet studies were truly multiple interventions that also included an exercise component-- too this was especially truthful for the low-fat studies.  The Ornish diet, for example, has a physical action component, whereas most of the low-carb studies didn't offering physical action guidelines.


The meta-analysis past times Johnston too colleagues is useful too adds to our torso of noesis on diets too health.  However, due to its odd inclusion criteria, it must locomote interpreted amongst slap-up caution-- which has non been the representative inward the media stories I've seen.  It doesn't truly own got much to enjoin virtually the relative effectiveness of low-fat vs. low-carbohydrate studies, because the inclusion criteria for each were too then unlike that nosotros can't lead compare them inside the context of this paper.  Unfortunately, the newspaper doesn't build that especially clear, which allowed it to locomote widely misinterpreted.

Previous meta-analyses, such every bit Hession et al, had balanced inclusion criteria that let us to lead compare low-fat to low-carb diets.  They reported just what anyone would facial expression who is familiar amongst the weight loss diet literature:
  1. At vi months, low-carb diets consistently Pb to greater weight loss than low-fat diets. 
  2. At ane year, the departure has all but disappeared. 
  3. Neither diet produces especially impressive weight loss at ane yr or more.
  4. The weight loss effectiveness of typical low-fat diets tends to locomote minor at all fourth dimension points.



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