Randomized study comparing four popular diets signals slight edge for Atkins over higher-carb options

Shelley Wood

March 06, 2007

Stanford, CA - Dieters and their physicians can be reassured that a low-carb diet is a safe and effective option for losing weight, on the basis of new randomized trial results comparing four popular diets ranging from low-carbohydrate to low-fat[1]. Results from the Atkins-Traditional-Ornish-Zone (A TO Z) trial found that premenopausal women randomized to the Atkins diet lost statistically more weight than women on the Zone diet and numerically more than the other two diets.

"This isn't the end of the obesity epidemic; this isn't a huge effect," lead author Dr Christopher Gardner (Stanford University Medical School, CA) emphasized to heart wire . "This is modest weight loss in all four groups, and it's a little bigger in the Atkins group, but none of the groups were following their diets well at 12 months. . . . We had people who lost more than 30 pounds on all four diets, and twice as many did that on Atkins than on the other diets, so it does suggest that you don't necessarily need to follow the low-fat/high-carb diet that we've depended on for 20 years."

In fact, says Gardner, all of the diets studied worked "about the same."

"Maybe that says we should give people a little more flexibility in how they try to lower their calories, because it's possible that a high-fiber diet helps some people, a high-protein diet helps another person, and a high-fat diet helps another."

Gardner et al's study appears in the March 6, 2007 issue of the Journal of the American Medical Association.

Patients randomized to 12 months on one of four diets

Investigators randomized 311 overweight/obese women between the ages of 20 and 50 to one of four diets containing incrementally more carbohydrates: the Atkins diet (very low-carb); the Zone diet (low-carb); the LEARN diet (low-fat/high-carb, based on national dietary guidelines), and the Ornish diet (very high in carbohydrates, very low-fat). All study participants were given books explaining the diet to which they'd been assigned and attended weekly instruction for eight weeks during the first two months on the diet, then remained on the diet for an additional 10 months.

After one year, women on the Atkins diet lost significantly more weight than did women on the Zone diet, and weight loss was numerically greater on Atkins than on the other two diets. There were no statistically significant differences in weight loss among women on the Ornish, LEARN, or Zone diets. Improvements in HDL cholesterol and triglyceride levels were greater in Atkins patients at 12 months, as compared with the other diet groups, although differences were only statistically significant for Atkins vs Ornish (for HDL) and Atkins vs Zone (for triglycerides); LDL levels appeared to favor the LEARN and Ornish diets as compared with the Atkins diet, but not to a statistically significant degree at 12 months. Fasting insulin and glucose levels were no different between the four groups; however, after one year, participants on the Atkins diet experienced systolic blood-pressure lowering that was significantly greater than that seen in any other group.

Changes from baseline at 12 months

Outcome Atkins Zone LEARN Ornish
Weight (kg) -4.7 -1.6 -2.6 -2.2
LDL (mg/dL) 0.8 0.0 0.16 -3.8
HDL (mg/dL) 4.9 2.2 2.8 0.0
Triglycerides -29.3 -4.2 -14.6 -14.9
Systolic BP -7.6 -3.3 -3.1 -1.9

"After all those [statistical] adjustments . . . everything that was still significant favored Atkins," Gardner observed to heartwire . "More weight loss than Zone, better triglycerides than Zone, better HDL than Ornish, better blood pressure than all three. Is it fantastic? Should everyone be on an Atkins diet? No, we can't say that yet. But this says there is something really interesting, I think, about carbohydrates and the emphasis really seems to be on cutting back those simple carbs."

Indeed, Gardner added, if there was one thing in common between the four diets it was an emphasis on reducing intake of simple carbohydrates and added sugars.

But Gardner also noted that carbs do not tell the whole story; tellingly, the authors did not see an incremental decrease in weight loss to correspond with increasing carbohydrates. For example, the Zone diet, which restricts carbohydrate consumption to 40% of the diet, had the smallest amount of mean weight reduction, whereas weight loss in the Ornish diet, where carbs make up the bulk of the diet, was not significantly different from Atkins. Gardner suggests that one reason for the success of the Atkins and Ornish diets is their simplicity: cut carbs or cut fats. By contrast, the Zone diet has "a lot more rules," and people may have simply found it too difficult to follow closely.

How popular diets stack up

Dr Gary Foster (Temple University, Philadelphia, PA), whose group is also conducting a randomized controlled trial including a low-carb diet arm, looking at two-year outcomes, commented on Gardner et al's findings for heartwire .

"This study is important because it compares popular diets that are used by many overweight Americans to lose weight. So to have some data on how these stack up against each other is really helpful. The results seem to support by and large what previous work at one year has shown, meaning that the reduction is not much different between the groups at one year."

Foster also singled out the importance of the lipid findings, calling them "unsurprising," since they go in the direction of other low-carb diet studies, suggesting that a low-carb diet seems to increase HDL and lower triglycerides, without having a detrimental impact on LDL.

"This suggests that low-carbohydrate diets are not as dangerous as people might have previously thought, and this study reinforces that notion from a lipid perspective and from a weight perspective. I think what we have to be careful about is what else is consumed besides the carbohydrate. Does it make a difference what type of fat or protein you consume? We have no clinical trials looking at that."

Also, he pointed out, a mean LDL change of 0.8 in the Atkins group means that almost as many people had LDL increases as decreases.

"These data support the notion that our concerns about lipid profiles on an Atkins-like diet were probably not warranted, but having said that, a lot of these mean values with lots of variability around them need to be looked into further."

Overall, he cautioned, "The lipid story is gradually emerging, but it's still unresolved."

Future research should look for factors that account for varying lipid responses to different diets, Foster said. "Is it genetic factors, or people with high baseline values vs low baseline values, or people with certain amounts of insulin sensitivity? In other words, are there behavioral or biological markers that can predict success with these diets, and, equally important, that can predict adverse effects of certain types of diets?

These questions are fodder for future studies, Foster said.

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