From Heartwire
Shelley Wood
January 25, 2010 (Durham, North Carolina) — A new randomized trial comparing a low-carbohydrate diet with a low-fat diet in combination with the weight-loss drug orlistat has found that both strategies produced meaningful weight loss among hospital outpatients over a one-year period [1]. Strikingly, however, the low-carb diet appeared to produce significant improvements in blood pressure.
According to Dr William S Yancy Jr (Duke University, Durham, NC), lead author on the study, this is the first time the low-carb diet has been pitted against a diet drug in combination with a different diet. It is also one of the first studies to compare weight-loss strategies in patients who also have other known medical problems, including high blood pressure, diabetes, arthritis, etc.
Yancy et al's findings are published in the January 25, 2010 issue of the Archives of Internal Medicine.
Almost 10% Weight Loss at One Year
Yancy et al's study randomized 146 overweight or obese outpatients (mean age 52, mean body-mass index [BMI] 39.3) to either a low-carbohydrate, ketogenic diet, or to orlistat (120 mg, three times daily) and a low-fat diet over 48 weeks, with regular group meetings to boost diet adherence. At the end of the study period, weight loss was similar in both groups, at roughly 10% (approximately 20 to 25 pounds). Of note, almost 80% of the low-carb group and almost 90% of the orlistat/low-fat group completed the full 48-week follow-up.
Improvements in HDL and triglycerides were seen in both groups, LDL levels improved in the orlistat/low-fat diet group only, while glucose, insulin, and HbA1c levels improved in the low-carb group only, although none of these differences were statistically meaningful. By contrast, both systolic and diastolic blood-pressure levels declined in the low-carb group only, a statistically significant difference between weight-loss groups.
"It's not surprising that the blood pressure improved," Yancy told heartwire , adding that improvements in blood pressure are common in weight-loss trials. "But it was surprising that, with similar weight loss, blood pressure would improve more in one group than the other."
While there are a number of explanations for the blood-pressure differences between weight-loss strategies, Yancy speculated that it might be related to the known diuretic effect of low-carb diets.
"We've looked at that in the past, and it seems to occur in the first couple weeks of the diet and doesn't seem to be a big factor after that, but that could contribute to the differences seen here. The other thing is that low-carb diets are thought to reduce insulin levels more so than a high-carb diet. There are several different mechanisms that insulin has with the vascular system that might cause increased blood pressure, so if you decrease insulin your blood pressure might decrease as well."
No Significant Differences in Lipid Changes
Other low-carb diet studies have also reported improvements in lipid parameters compared with low-fat diets: something that was not seen in the current study to a statistically significant degree. Yancy attributes this in part to an aggressive attempt on the part of investigators to include as many patients as possible at the 48-week follow-up.
"A big criticism of other weight-loss trials is there are a lot of lost or missing data," he explained. "We tried to avoid that as much as possible, and as a result, some of these folks who came back for their final measurements who hadn't really been following their diets kind of watered down the results."
For example, in the paper, the authors report differences in heart-disease risk factors at interim time points and note that, out to 36 weeks, the two interventions "appeared to have differential effects on fasting serum lipid and lipoprotein levels over the first 36 weeks," but that "these differences converged by 48 weeks."
In another important finding, Yancy et al point out that while a small number of study participants initiated hypertension or diabetes medications over the course of the study in both diet groups, a much higher number actually decreased or discontinued their dosages, with a higher proportion of patients discontinuing or lowering their dosages in the low-carb group.
Referring to the blood-pressure effects of the low-carb diet, Yancy pointed out that investigators "don't really know the full effect of the diet intervention because patients were actually taking less medication."
Options for Patients
The key message from the paper is not that one diet is superior to another, Yancy concluded. "Different interventions appeal to different people," he told heartwire . "We have a big weight problem in our society, and this study gives us two different options, both of which worked quite well. And if you happen to have blood-pressure problems and you are trying to kill two birds with one stone, the low-carb option might be a better option than the orlistat option."
Of note, he added, orlistat is not associated with increases blood pressure, although other diet drugs are, including sibutramine, for which the FDA recently released an updated warning on CVD risks.
Yancy, as well as second author Dr Eric C Westman (Duke University Medical Center) disclosed having received clinical research grants from the Robert C Atkins Foundation.
References
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