Thursday, May 18, 2006

Diet Study: Confusing Data Makes Sense!

After scratching my head for a few days trying to tease out just what it was in the recent study, Separate effects of reduced carbohydrate intake and weight loss on atherogenic dyslipidemia, that was so baffling, I found the likely explanation.

What baffled me was that the researchers concluded in their abstract that "Moderate carbohydrate restriction and weight loss provide equivalent but nonadditive approaches to improving atherogenic dyslipidemia. Moreover, beneficial lipid changes resulting from a reduced carbohydrate intake were not significant after weight loss."

In the results section of the full-text of the paper however, it's clear the low-carb diets induced greater improvements in cholesterol and weight. As the researchers stated in the full-text:

"In the initial diet, stable-weight phase of the study, the 26%-carbohydrate, low-saturated-fat diet resulted in reductions from baseline in total cholesterol, triacylglycerol, apo B, and total:HDL cholesterol that were greater than the changes observed in the group remaining on the 54%-carbohydrate diet. However, the difference in the change in LDL cholesterol between the 26%-carbohydrate diet and the control diet was not significant by post hoc analysis (P = 0.13). Despite our effort to maintain constant weight, the 26%-carbohydrate, low-saturated-fat diet group lost more weight than did the 54%-carbohydrate group during the stable-weight period. There was also a trend for a greater reduction in percentage body fat with the lower-carbohydrate diets (P less than 0.02, analysis of variance). The significance of the lipoprotein differences between the 26%- and 54%-carbohydrate groups persisted after adjustment for the change in body weight for total cholesterol (P = 0.01), triacylglycerols (P = 0.02), apo B (P = 0.001), and total:HDL cholesterol (P = 0.002), whereas differences in LDL cholesterol and LDL-IV between groups became marginal (P = 0.09 and P = 0.11, respectively)."

Where the findings get confusing is when the researchers continue:

"In contrast with the findings during the initial diet, stable-weight phase, weight loss and stabilization led to reductions in each of these variables that were significantly greater with the 54%-carbohydrate diet than with the 26%-carbohydrate, low-saturated-fat diet."

How does that happen? I wondered if it really was just the weight loss - not the macronutrient composition - that truly was responsible in the various findings to date that were so favorable for low-carb diets. Then again, study after study also shows data that low-fat macronutrient mix diets - those that are high in carbohydrate - have a negative effect on HDL and triglycerides.

So what gives?

As I said above, I think I've found the likely explanation, and it's from Dr. Mike Eades. He too read and re-read the paper, crunched the numbers over and over and then after some head-scratching - viola! - a very interesting and likely explanation.

I couldn't explain it better, so I hope you'll take some time to head over to Dr. Mike's Blog and have a read yourself!

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