Making the Rounds Around the Research of Low-Carb Diets

Over the coming hours and days, you'll have a smorgasbord of articles to tell you all about the soon-to-be-released study - Comparison of Atkins, Zone, Ornish and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women (aka The A to Z Weight Loss Study) - being published in JAMA later today.

The results are already leaking out in various newspapers, so if you want a preview, you can read here or here or here.

While this study will be a media darling the next few days, I thought I'd highlight some other research that is just as important to our overall understanding of carbohydrate restriction, yet remains virtually ignored by the media!

I'll get to the JAMA study later this week since the findings really are nothing new nor a surprise to those of us who already understand that carbohydrate restriction works.

So, without further ado - in the March issue of Surgical Endoscopy, we find The effect of a low-carbohydrate diet on the nonalcoholic fatty liver in morbidly obese patients before bariatric surgery. In this study researchers investigated the effect of a very low-carbohydrate diet over four-weeks in 14 pre-op patients before bariatric surgery. All were morbidly obese and scans revealed non-alcoholic fatty liver disease (NAFLD).

NAFLD with enlargement of the left lobe of the liver can complicate bariatric surgery, so the researchers wanted to see the effect diet would have on liver density before surgery. After four weeks, there was a statistically significant increase in liver density and statistically significant decrease in liver volume. The researchers concluded, "The findings show that 4 weeks of a very low carbohydrate diet reduces liver fat content and liver size, particularly of the left lobe. This approach may render bariatric surgery or any foregut operations less difficult in morbidly obese patients and may be a useful treatment for nonalcoholic fatty liver disease."

Next up, in the February issue of American Journal of Physiology, Heart & Circulatory Physiology, we find Effects of Low Carbohydrate Diet on Vascular Health: More than just Weight Loss (pubmed citation) reviewing this study, Restoration of Coronary Endothelial Function In Obese Zucker Rats By A Low Carbohydrate Diet, published in the same issue.

In the latter, the study investigated endothelial function in obese rats fed a low carbohydrate or normal rat diet, the researchers concluded that "obesity-induced impairment in endothelial dependent vasodilation of coronary arterioles can be dramatically improved with a low carbohydrate diet most like(ly) through the production of a hyperpolarizing factor independent of NO." In the review (first link above) it was concluded that "Focardi et al demonstrates a novel mechanism of improved coronary vascular function with LC (low-carb) diet during metabolic syndrome. This study implicated a role for EDHF (endothelium derived hyperpolarizinf factors) in dietary interventions that may improve the cardiovascular complications of metabolic syndrome."

In simple English - the rats with metabolic syndrome did significantly better with a low-carb diet than their normal chow.

Another animal model study - A High Fat, Ketogenic Diet, Induces a Unique Metabolic State in Mice - in the American Journal of Physiology, Endocrine Metabolism, was a really cool study. In this study researchers compared the physiologic and metabolic effects of four different diets - normal chow (control group), a high-fat/high-sucrose diet, a ketogenic low-carb diet, and a calorie restricted (66% normal calories) optimal nutrition diet (CRON). The researchers found that the mice on the ketogenic diet ate the same calories as those on the control chow or the high-fat/high-sucrose diet, but their weight dropped and then stablized at 85% of their initial baseline weight - almost identical to those mice fed the CRON diet and allowed just 66% of their normal calories.

Mice grew obese on the high-fat/high-sucrose diet (remember, they were not eating more calories!) and when they were transitioned to a ketogenic diet, they lost their excess weight, improved glucose metabolism and increases energy expenditure. Need I say more?

Back in January, Metabolism published the study, Effects of a carbohydrate-restricted diet with and without supplemental soluble fiber on plasma low-density lipoprotein cholesterol and other clinical markers of cardiovascular risk, in which researchers investigated the effect of dietary fiber in a carbohydrate restricted diet (CRD). The researchers compared two groups of subjects following a carbohydrate restricted diet - group one was given a fiber supplement and group two a placebo; after 12-weeks both groups lost weight and body fat, improved systolic blood pressure, waist circumference and blood glucose levels.

Interesting finding - in both groups HDL and triglycerides improved (10% and -34% in fiber group; 14% and -43% in placebo group); LDL decreased by 17.6% at week 6 and 14.1% at week 12 in the fiber group; and a significant reduction, 6% happened at week 12 in the placebo group. As the researchers concluded, "We conclude that although clearly effective at lowering LDL-C, adding soluble fiber to a CRD during active and significant weight loss provides no additional benefits to the diet alone. Furthermore, a CRD led to clinically important positive alterations in cardiovascular disease risk factors."

So, while the rush will be on later today to pick apart and analyze the JAMA study, keep in mind it's not the first, nor will it be the last that confirms a carbohydrate restricted diet is a scientifically supported dietary approach for weight loss, cardiovascular improvement and improvement to blood sugars, cholesterol and the features of metabolic syndrome. It's also not the only recently published study investigating carbohydrate restriction or comparing it to other dietary approaches.