Pounds Creep Back with Low-fat, Low-Carb Diets

Diets that cut out fats or carbohydrates may not lead to sustained weight reduction….

Mona Boaz, PhD, of E. Wolfson Medical Center in Holon, Israel, and colleagues at the World Congress on Insulin Resistance, Diabetes stated that,  “In addition to energy restriction, some diets emphasize manipulation of macronutrient composition to promote weight loss.” “Such diets may be broadly classified into low-fat and low-carbohydrate diets.”

But the manipulation of macronutrient composition did not seem to have significant effects on weight loss in the long run, Boaz and colleagues reported. “We ran a random effects model and we saw nothing.” “In the short term, you usually see a benefit with [macronutrient composition manipulation], but in the long run, there’s no difference.”

Boaz added that both low-fat and low-carbohydrate diets were associated with poor adherence and high attrition rates. However, they often have poor long-term performance, Boaz and colleagues claimed.

To determine whether either of these diets had any advantages in terms of sustained weight loss, Boaz and colleagues conducted a meta-analysis of several randomized, clinical trials in healthy adults, which compared low-carbohydrate diets to low-fat diets.

They found four studies, totaling 1,878 patients. Of that total, 941 were on the low-carbohydrate diet and 937 were on a low-fat diet. Two of the studies targeted weight loss as the primary endpoint, and two looked at maintenance of weight loss using meal replacement products.

Boaz said the overall compliance was poor and the attrition rate was high across studies.

Based on a random effects model, she and her colleagues said they could not identify any significant advantage to either diet strategy (standardized difference in means -0.07, 95% CI -0.3 to 0.4, P=0.7).

Boaz said the possible explanations included the between-group difference in macronutrient content, which was much smaller than planned. Also, poor compliance and high attrition rates existed despite the fact that patients in the studies were motivated and the follow up was structured and supervised.

Her group concluded that novel weight loss strategies need to be investigated. Future studies on the diets themselves are also needed, Boaz added. She said the timing of macronutrient may have an effect on diet outcomes, and that is currently under investigation.

• Explain that a meta-analysis of four studies since 2009 on the outcomes of low-fat or low carbohydrate diets found no differences between the diets.
• Note that the investigators were hampered by poor compliance and high attrition rates in both types of diets, and they pointed to a need for new diet strategies.
• Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Boaz M, et al “Macronutrient composition in weight loss diets — a meta-analysis” WCIR 2011