Low-carb and Mediterranean diets beat low-fat for weight-loss, lipid changes at two years

Shelley Wood

July 16, 2008

Beer-Sheva, Israel - Both a low-carbohydrate diet or a Mediterranean-style diet may be "effective alternatives" to a low-fat diet, with more favorable effects on lipids and/or glycemic control, new research suggests[1]. The two-year study, which managed to keep almost 85% of the 322 study participants on one of the three diets for the entire period, offers the hope that weight-loss diets can be tailored to personal preferences, without sacrificing efficacy, researchers say.

"Several recent one-year dietary studies have led the American Diabetes Association to state in January 2008 that low-carb diets should be considered for a maximum of one year," lead author on the study, Dr Iris Shai (Ben Gurion University of the Negev, Beer-Sheva, Israel), told heart wire . "The current two-year study suggests that one low-fat diet doesn't fit all, meaning that the old paradigm should be reconsidered."

Shai and colleagues publish the results of the Dietary Intervention Randomized Controlled Trial (DIRECT) in the July 17, 2008 issue of the New England Journal of Medicine.

Diet options

At the start of the study, DIRECT subjects were middle-aged (mean age 52 years) and mildly obese (body-mass index=31). All participants were randomized to one of three diets: low-fat/restricted-calorie diet; Mediterranean/restricted-calorie diet; or low-carbohydrate diet, with no restriction on calories. After two years, adherence to their respective diets ranged from more than 90% in the low-fat group, to 85% in the Mediterranean diet group, to 78.0% in the low-carb group.

Weight loss occurred in all three groups over the 24 months but was greater in the Mediterranean and low-carb groups. In men—who made up the bulk of the study cohort—weight loss was greatest in the low-carb group, whereas women—just 45 in the study cohort—appeared to lose more weight on the Mediterranean diet. When the analysis was performed just in the 272 "completers" who adhered to the diet for the entire study period, the pattern of weight loss associated with each diet was similar.

Weight loss

Group Low-fat (kg) Mediterranean (kg) Low-carb (kg)
All patients -2.9 -4.4 -4.7
All completers -3.3 -4.6 -5.5
Men -3.4 -4.0 -4.9
Women -0.1 -6.2 -2.4

Changes in lipid parameters were also most striking in the low-carb and Mediterranean-diet groups. HDL increases and triglyceride decreases were most pronounced in the low-carb group, while reductions in LDL cholesterol were greatest in the Mediterranean-diet group. Reductions in total cholesterol/HDL ratio were greatest in the low-carb group, closely followed by the Mediterranean-diet group.

Lipid changes

Parameter Low-fat (mg/dL) Low-carb (mg/dL) Mediterranean (mg/dL)
HDL +6.4 +8.4 +6.3
LDL -0.05 -3.0 -5.6
Triglycerides -2.8 -23.7 -21.8
Total cholesterol/ HDL ratio -0.6 -1.1 -0.9

In the subset of patients with diabetes—just 36 out of 322 subjects—the Mediterranean diet appeared to improve fasting plasma glucose levels. According to Shai, the results suggest that "one size doesn't fit all."

"The current results suggest that Mediterranean and low-carbohydrate diets are effective alternatives to low-fat diets," she said. "The more favorable effects on lipids with the low-carbohydrate diet and on glycemic control with the Mediterranean diet suggest that personal preferences and metabolic considerations might inform individualized tailoring of dietary interventions."

An "optimal" study environment

One of the unique features of the study was its location: the DIRECT study was conducted at a nuclear research center in Israel with an on-site cafeteria and medical clinic. Participants in the trial ate their main meal of the day—lunch—in the workplace cafeteria, where food choices were carefully controlled and labeled. On-site dieticians worked regularly with participants to help them adhere to their diets. Indeed, the Nuclear Research Center Negev itself, along with the Robert C and Veronica Atkins Foundation—the low-carb diet in DIRECT was based on the Atkins diet—helped fund the study.

In the paper, Shai et al acknowledge that the setting was perfectly suited to a study of this kind, but that this doesn't mean these diets would not have worked elsewhere. "We took advantage of the isolated place, which is highly monitored by an excellent internal medical department, and a set of cafeterias [whose menus] we could modify," she told heart wire . And in fact, she said, "we do believe that this optimal model could be applied in other workplaces, once the manager prioritizes this kind of long-term health-promotion project."

Why do they work?

Asked what she thinks is behind the success of the low-carb and Mediterranean diets, Shai said that, at least in the case of the Mediterranean diet, reducing calories may be slightly easier when moderate fat consumption is permitted.

In the case of the low-carb diet, there are a number of possible explanations, she says.

"First, the advantage of this strategy is that the 'enemy'—carbohydrates—is well defined and once learning it, the [dieter] knows what to stay away from, without counting calories," Shai told heart wire . "And after the initiation phase, the dieter has less craving. Second, we assume that a relatively high-protein diet does contribute to higher satiety. Third, the immediate response of the body to weight loss may encourage the dieter."

Commenting on the study for heart wire , Dr Eric Westman (Duke Clinical Research Institute, Durham, NC), a long-time skeptic of low-fat diets, acknowledged that the low-carb diet craze of the early 21st century has died down, something he can't explain. "There is this study, and there are two additional National Institutes of Health studies in the US that are progressing well, so I don't know what the push-back was. Some have speculated that Dr [Robert C] Atkins dying or the company going bankrupt made the wind change, even though the science has just marched along. It's a mystery to me."

Like Shai, Westman thinks it might be time to "get beyond that old low-fat diet" and that, slowly but surely, this is actually starting to happen.

I'm reading my daughter's high school health textbook, and it's like a religion: 'Everyone should follow a low-fat diet' and 'Saturated fats kill you, ' and that's just wrong, plain wrong.

"I'm reading my daughter's high school health textbook and it's like a religion: 'Everyone should follow a low-fat diet' and 'Saturated fats kill you,' and that's just wrong, plain wrong," he told heart wire . "There are more people coming out of the closet saying they weren't part of this low-fat diet thing all along, but I guess they felt they couldn't speak up. I think that what we're soon going to find is that nobody's going to be defending the 30% fat, low-fat diet anymore."

Indeed, AHA past-president Dr Robert Eckel (University of Colorado Health Sciences Center, Denver), points out that Shai et al's study used the outdated 2000 AHA guidelines as the template for its low-fat diet.

"The AHA updated its dietary guidelines in 2005, which are quite different from the diet that's quoted here," he told heart wire . "The dietary fat restriction at 30% of calories is no longer part of the AHA guidelines, and the saturated-fat content has been reduced from 10% to 7% and the cholesterol content from 300 to 200 mg/day. I think it's a little bit unfair to kind of generalize that the AHA, number one, stands for a low-fat diet; that's no longer the case. And number two, there is some kind of mysterious benefit of being on the Mediterranean and low-carb diets over time that doesn't necessarily at this point have any explanation."

But Eckel rejects the idea that saturated fats could be embraced by any legitimate weight-loss approach. "Anything that would endorse the Atkins-type of food-intake pattern would not be something that the AHA would back," he said firmly. "Saturated fats raise LDL cholesterol—I don't think many people would disagree with that. . . . At this point limiting saturated fats is still a position the AHA would claim, and I think that's consistent with the National Cholesterol Education Program guidelines, the American Diabetes Association, the US Department of Agriculture. I don't think there is any major professional organization at this point that's willing to throw in the towel on saturated fats and say they are unimportant."

Both Westman and Eckel had some niggling questions about Shai et al's study. Westman pointed out that there were only 10 people in each diet group with diabetes and as such the effects of the Mediterranean diet in this group may have been "overstated." It's likely that both the Mediterranean and low-carb diets are beneficial in diabetics, he says, since both were higher in fat and lower in carbohydrates.

Eckel, for his part, points out that a study cohort that is 86% male is unusual in a diet study, which typically enrolls more women. "How generalizable this study is to women with obesity is not clear to me," he said.

He also pointed to the lack of emphasis on physical activity in the study—something he believes is key to keeping weight off long term.

More tools in the trunk
I don't think there is any major professional organization at this point that's willing to throw in the towel on saturated fats and say they are unimportant.

What the authors, as well as Westman and Eckel, agree is on the notion of different options for different people, with different medical concerns. Eckel points to the AHA's "No Fad Diet," which offers three strategies for people to choose from, including a low-carb option. Westman stresses the need for physicians treating overweight and obese patients to stop quibbling over diets. "In the end, all of these lifestyles work," he said. "Low-fat diets work, but the low-carb and Mediterranean diets are stronger, and that's good because we need more tools.  All this 'my diet is better than your diet'—we need to get beyond that. What we really want are the metabolic outcomes, and there are many ways to go about it."

Westman also points out that a decades-old bias against the possibility of higher-fat diets having any benefits to them has hampered research. "It's time to study low-fat and high-fat diets with cardiac end points and genetic markers to tailor diets for cardiac risk reduction," he says.

And until that time, Eckel remains unconvinced. "Until we have studies . . . that show me that heart attacks, cancer, or other comorbidities of obesity are reduced in terms of hard end points, I'm not going to be convinced that any diet is better, even though you may be down a few more kilograms on that one diet," Eckel told heart wire . "I'm not denying the success of [Shai et al's] study, I'm just saying that this is more hand-waving with soft outcomes, which really don't get at the question: can people lose weight for five, 10, 15, and 20 years, and what does that do to risk for heart disease, stroke, and mortality?"

The authors disclose having no conflicts of interest. Westman disclosed receiving unrestricted research funds from the Atkins Foundation. Eckel disclosed having no relevant conflicts of interest.


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