Low-Carbohydrate Versus Low-Fat Diet in Managing Obesity
Low-Carbohydrate Versus Low-Fat Diet in Managing Obesity
The initial literature search identified a total of 1405 potentially relevant articles. After excluding studies conducted in 2000 and earlier, the number of relevant studies decreased to 1004. A total of 776 studies were conducted with human subjects. Figure 1 shows the flow diagram that describes the steps in the selection of the 17 studies that were reviewed for the purpose of this meta-analysis.
(Enlarge Image)
Figure 1.
Flow diagram of the systematic review.
The studies selected were randomized controlled trials (RCT) with weight change as one (or the only) of their primary outcomes. In four of these studies, the investigators chose to compare commercially available LCDs or LFDs. The reviewed studies were significantly heterogeneous in their methodology as demonstrated by I (Figs. 2 and 3).
(Enlarge Image)
Figure 2.
Weight loss at 6 months. CI, confidence interval.
The selected 17 RCTs included a total of 1958 participants, with 924 and 1034 individuals randomized to an LCD and an LFD, respectively. The mean age of all of the participants ranged from 27 to 60 years. Ten studies reported ethnicity/race. Seven studies reported weight loss at 12 months, 1 study at 18 months, and 3 trials at 24 months. Four studies compared brand-name diets. Specifically, the LCDs included the Atkins and Zone diets. LFDs included the Slim Fast; Weight Watchers; South Beach; Conley; Lifestyle, Exercise, Attitudes, Relationships, and Nutrition; and Ornish diets. The key characteristics of each study are presented in Table 1 and Table 2 . The majority of the studies (12/17 trials), were conducted in the United States, 3 in Europe (1 in the United Kingdom and 2 in Germany), 1 in Israel, and 1 in Australia.
The risk of bias for each of the 17 studies was assessed using the Cochrane Collaboration tool; the results are presented in Table 3 . Sixteen studies were at high risk of bias and one study was at unclear risk of bias.
At 6 months, the estimated mean weight loss was −1.439 kg (95% CI −2.319 to −0.558) for the individuals who followed an LCD compared with participants who followed an LFD (P < 0.001; Fig. 2).
At 12-month follow-up, the difference in the mean weight change between the LCD and the LFD was smaller, −0.769 kg (95% CI −1.361 to −0.178) but remained statistically significant (P < 0.010; Fig. 3). The reduction in the mean difference of the weight loss between the LCD and the LFD from 6 to 12 months suggests an attenuation of this finding over time.
(Enlarge Image)
Figure 3.
Weight loss at 12 months. CI, confidence interval.
Although the composition of the LCD and LFD differed in each individual study, overall the participants who followed an LCD consumed <45% of calories from carbohydrates, and the participants on an LFD included <30% fat in their diets. Nutritional counseling was an additional intervention in all of the studies and was offered either as individual counseling and/or in small groups. This counseling was available and offered weekly or biweekly in the beginning of each diet and offered monthly or less often after the first 1 to 2 months of the dietary intervention. The duration of these counseling sessions varied among the studies and ranged from 30 to 90 minutes per session. In some studies, these counseling interventions were supplemented by e-mails and telephone calls to remind participants and motivate those with adherence issues. In some studies, the investigators offered exercise recommendations to their participants, although exercise was not one of their interventions.
Results
The initial literature search identified a total of 1405 potentially relevant articles. After excluding studies conducted in 2000 and earlier, the number of relevant studies decreased to 1004. A total of 776 studies were conducted with human subjects. Figure 1 shows the flow diagram that describes the steps in the selection of the 17 studies that were reviewed for the purpose of this meta-analysis.
(Enlarge Image)
Figure 1.
Flow diagram of the systematic review.
Study Characteristics
The studies selected were randomized controlled trials (RCT) with weight change as one (or the only) of their primary outcomes. In four of these studies, the investigators chose to compare commercially available LCDs or LFDs. The reviewed studies were significantly heterogeneous in their methodology as demonstrated by I (Figs. 2 and 3).
(Enlarge Image)
Figure 2.
Weight loss at 6 months. CI, confidence interval.
The selected 17 RCTs included a total of 1958 participants, with 924 and 1034 individuals randomized to an LCD and an LFD, respectively. The mean age of all of the participants ranged from 27 to 60 years. Ten studies reported ethnicity/race. Seven studies reported weight loss at 12 months, 1 study at 18 months, and 3 trials at 24 months. Four studies compared brand-name diets. Specifically, the LCDs included the Atkins and Zone diets. LFDs included the Slim Fast; Weight Watchers; South Beach; Conley; Lifestyle, Exercise, Attitudes, Relationships, and Nutrition; and Ornish diets. The key characteristics of each study are presented in Table 1 and Table 2 . The majority of the studies (12/17 trials), were conducted in the United States, 3 in Europe (1 in the United Kingdom and 2 in Germany), 1 in Israel, and 1 in Australia.
The risk of bias for each of the 17 studies was assessed using the Cochrane Collaboration tool; the results are presented in Table 3 . Sixteen studies were at high risk of bias and one study was at unclear risk of bias.
Effect of Diet on Weight
At 6 months, the estimated mean weight loss was −1.439 kg (95% CI −2.319 to −0.558) for the individuals who followed an LCD compared with participants who followed an LFD (P < 0.001; Fig. 2).
At 12-month follow-up, the difference in the mean weight change between the LCD and the LFD was smaller, −0.769 kg (95% CI −1.361 to −0.178) but remained statistically significant (P < 0.010; Fig. 3). The reduction in the mean difference of the weight loss between the LCD and the LFD from 6 to 12 months suggests an attenuation of this finding over time.
(Enlarge Image)
Figure 3.
Weight loss at 12 months. CI, confidence interval.
Diet Composition and Additional Interventions
Although the composition of the LCD and LFD differed in each individual study, overall the participants who followed an LCD consumed <45% of calories from carbohydrates, and the participants on an LFD included <30% fat in their diets. Nutritional counseling was an additional intervention in all of the studies and was offered either as individual counseling and/or in small groups. This counseling was available and offered weekly or biweekly in the beginning of each diet and offered monthly or less often after the first 1 to 2 months of the dietary intervention. The duration of these counseling sessions varied among the studies and ranged from 30 to 90 minutes per session. In some studies, these counseling interventions were supplemented by e-mails and telephone calls to remind participants and motivate those with adherence issues. In some studies, the investigators offered exercise recommendations to their participants, although exercise was not one of their interventions.
Source...