I've written previously regarding the issue of low carb diets, whether they're effective, and for whom they're effective. If you're a regular reader of mine, then you undoubtedly know my stance on carbs: That they can be good, bad, or neutral depending on the circumstances within which you find yourself. And the latest bit of research conducted on this subject only adds to the relativism.
The Latest Research
Lydia A. Bazzano et al. recently conducted a randomized, parallel group trial on 148 obese men and women without cardiovascular disease and diabetes (1). The researchers' goal was to compare the effect of a low fat diet against the effect of a low carbohydrate diet on body weight and cardiovascular risk factors. The participants were divided into two groups, with one being instructed to limit their carbohydrate intake to less than 40 grams per day, and the other being instructed to limit their fat intake to less than 30% of total daily calories, with less than 7% of those fat calories coming from saturated fat (These instructions just so happen to reflect NCEP guidelines for reducing cardiovascular risk factors). Dietary counseling was given to both groups throughout the trial. Data on weight, cardiovascular risk, and diet composition was collected for both groups at the beginning of the trial, at three months in, six months in, and at 12 months.
What Did the Researchers Find?
By the end of the 12 month study 82% of the low fat group remained and 79% of the low carb group remained. While both groups experienced weight loss (though not a significant amount) and a reduction in cardiovascular risk, the low carb group saw a greater improvement. However, it should be noted that the low carb group didn't exactly follow the guidelines established for them by the researchers. Rather than limit their daily carb intake to less than 40 grams, participants consumed an average of 97, 93, and 127 grams of carbs per day at three, six, and 12 months respectively. Thus, the low carb group was not following an extremely low carb diet. This distinction is notable because the instructions given by the researchers to consume less than 40 grams of carbs per day would have put the low carb participants into a ketogenic state; thus meaning that the results from this study reflect what one might experience when following my own advice, which is that people who are relatively overweight or obese should limit their daily carb intake to 100-120 grams.
Regarding the low fat group, participants limited their average intake of fat to 45, 46, and 52 grams per day at three, six, and 12 months respectively. This amount of fat reflects my low-end recommendation of grams of fat per day for relatively active and fit individuals. Though the low carb group saw greater improvements than the low fat group, it's comforting to know that the low-end of my recommended daily fat intake didn't play havoc with the health of the low fat participants.
In terms of body composition and weight loss, the low carb group lost an average of about 12 lbs by the end of the trial while the low fat group lost about 4 lbs. Despite these differences in weight loss, both groups saw similar reductions in waist circumference, which suggests a similar reduction in abdominal fat. Upon considering the difference in weight loss vs the negligible difference in waist circumference, I'm led to think that the greater weight loss experienced by the low carb group could reflect glycogen depletion in the muscles and a loss of water weight. Without having accurate body composition measurements, however, I'm fain to declare certainty regarding this speculation.
Beyond body composition, the low carb group had greater improvements in their ratio of LDL ("bad" cholesterol) to HDL ("good" cholesterol). This improvement reflects a particular theory regarding cholesterol health, which states that high cholesterol and an imbalanced ratio of LDL to HDL is caused, in part, by low level systemic inflammation. This low level systemic inflammation is purportedly caused by, among many factors, insulin resistance, which of course leads to inefficient and unfavorable partitioning of dietary glucose within the body. It therefore makes sense, within the framework of this particular understanding of the cholesterol issue, that the low carb group fared better in terms of cardiovascular health than did the low fat group. I should note, though, that the low fat group actually saw slightly better improvements in fasting insulin and glucose levels; however, these improvements border on statistically insignificant (nevertheless, this finding does somewhat refute my claim that a low carb diet should better address the problem of insulin resistance than should a low fat diet).
Why This Study Matters
Good scientific studies are hard to come by these days. This particular bit of research is an example of one such "good" study. Diet adherence by the participants was relatively good (yes, the low carb group did consume double the amount of carbs per day than they were supposed to, but at least they were consistent!), and the results of this study were such that they offer potential answers to two important questions: 1) the results of this study support the claim that low fat diets can lead to weight loss, and 2) the results of this study reveal that low carb diets can be compatible with cardiovascular health.
This study also reveals certain shortcomings that arise from simple dietary guidelines, which call for the mere elimination or restriction of one particular macronutrient sans other, more critical, intervention strategies--such as calorie restriction and food choice. As the results from this study reveal, while both groups saw reductions in body fat, these reductions were minor. To quote obesity researcher Dr. Stephan Guyenet, who did his own right-up on this study: "Both groups went from obese to slightly less obese" (2). Big Whoop!
Way more needs to go into a weight loss strategy than the reduction of fat or carbohydrate alone.
The Take-away
The science of obesity and cardiovascular risk is multifaceted and complex; though our response to both of these issues need not be. Yes, we do need more complex solutions than restricting carbs or fat or certain food groups, but these solutions don't have to be much more complex.
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