Efficacy and Safety of Low-Carbohydrate Diets

Abstract

ETWEEN 1960 AND 2000 THE prevalence of obesity among adults aged 20 years to 74 years in the United States increased from 13.4% to 30.9%. [1][2][3] An estimated 325000 deaths and between 4.3% and 5.7% of direct health care costs (approximately $39-$52 billion) are attributed to obesity annually. 1,2 Results from the 1998 Behavioral Risk Factor Surveillance Survey indicate that roughly one third of US adults were trying to lose weight at that time, and another third were trying to maintain weight. 4 Recently, lowcarbohydrate diets have resurged in popularity as a means of rapid weight loss, yet their long-term efficacy and safety remain poorly understood.The first low-carbohydrate diet to have enjoyed popular success was that described by William Banting in the 1860s. 5 Banting claimed that he was never hungry and at the age of 66, in a period of a year, lost 46 of his initial 202 pounds. He wrote, "The great charms and comfort of the system are that its effects are palpable within a week of trial and creates a natural stimulus to persevere for a few weeks more." 5 While it is difficult to estimate the number of people who have followed low-carbohydrate diets, the number and popularity of articles and books from the lay press advocating their use attest to a high level of interest in and de-mand for these diets by the US public. The most popular text, written by cardiologist and long-time proponent Context Low-carbohydrate diets have been popularized without detailed evidence of their efficacy or safety. The literature has no clear consensus as to what amount of carbohydrates per day constitutes a low-carbohydrate diet. Objective To evaluate changes in weight, serum lipids, fasting serum glucose, and fasting serum insulin levels, and blood pressure among adults using low-carbohydrate diets in the outpatient setting. Data Sources We performed MEDLINE and bibliographic searches for Englishlanguage studies published between January 1, 1966, and February 15, 2003, with key words such as low carbohydrate, ketogenic, and diet. Study Selection We included articles describing adult, outpatient recipients of lowcarbohydrate diets of 4 days or more in duration and 500 kcal/d or more, and which reported both carbohydrate content and total calories consumed. Literature searches identified 2609 potentially relevant articles of low-carbohydrate diets. We included 107 articles describing 94 dietary interventions reporting data for 3268 participants; 663 participants received diets of 60 g/d or less of carbohydrates-of whom only 71 received 20 g/d or less of carbohydrates. Study variables (eg, number of participants, design of dietary evaluation), participant variables ( eg, age, sex, baseline weight, fasting serum glucose level), diet variables (eg, carbohydrate content, caloric content, duration) were abstracted from each study. Data ExtractionTwo authors independently reviewed articles meeting inclusion criteria and abstracted data onto pretested abstraction forms. Data SynthesisThe included studies were highly heterogeneous w...

Low‐carbohydrate (low & high‐fat) versus high‐carbohydrate low‐fat diets in the treatment of obesity in adolescents

“…There were no significant differences in the changes of any of these parameters among the three groups throughout the study. This finding is in line with other studies of low carbohydrate diets in youth (14–16) and adults (1,4,6). In the randomized controlled trial of Sondike et al (15) in youth, the low carbohydrate group showed a significant decrease in triglyceride level, although the difference among the groups did not reach statistical significance.…”

“…Mean Fat percentage was still lower as compared to baseline values. Our results are in line with several methodic reviews of studies done in adults (1,4,6). In one of the few randomized studies in youth that included a control group, Sondike et al (14) found an advantage for the low‐carbohydrate diet (20–40 g/day) over the low‐fat diet in both weight loss and decrease in BMI.…”

Low‐carbohydrate (low & high‐fat) versus high‐carbohydrate low‐fat diets in the treatment of obesity in adolescents

“…There were no significant differences in the changes of any of these parameters among the three groups throughout the study. This finding is in line with other studies of low carbohydrate diets in youth (14–16) and adults (1,4,6). In the randomized controlled trial of Sondike et al (15) in youth, the low carbohydrate group showed a significant decrease in triglyceride level, although the difference among the groups did not reach statistical significance.…”

“…Mean Fat percentage was still lower as compared to baseline values. Our results are in line with several methodic reviews of studies done in adults (1,4,6). In one of the few randomized studies in youth that included a control group, Sondike et al (14) found an advantage for the low‐carbohydrate diet (20–40 g/day) over the low‐fat diet in both weight loss and decrease in BMI.…”

Carbohydrate versus Energy Restriction: Effects on Weight Loss, Body Composition and Metabolism

“…2 a). Our results are consistent with those of Bravata et al [5] , whose meta-analysis of literature concerning Average serum insulin, leptin, and IGF-1 for each diet group at sacrifice. Average serum leptin ( a ) (n = 17 for PF, n = 16 for HC, HF, LC and DER) , insulin ( b ) (n = 17 for HF, n = 16 for PF, n = 14 for LC, n = 12 for HC and n = 11 for DER), and IGF-1 ( c ) (n = 11 for DER, n = 9 for LC, n = 8 for HC, n = 7 for HF and n = 6 for PF).…”

“…In contrast, carbohydrate restriction had little effect on any of these parameters, with the exceptions of glucose and insulin, when compared to the HF group. This study replicates clinical studies in humans [5] , agrees with previous rodent studies [9,21,22] , and provides further evidence that a negative energy balance is critical for reducing weight and reversing obesity-related metabolic changes.…”

Low-Fat Versus Low-Carbohydrate Weight Reduction Diets

“…In contrast to the lack of a change in LDL and HDL in response to the low-carbohydrate diet, there was a significant reduction in triglycerides within this group compared with no significant change within the low-fat group. This response has been consistently reported in other studies comparing a low-carbohydrate and low-fat weight reduction diet (12). It has been speculated that this result is due to a combination of a decrease in the VLDL production rate and an increase in triglyceride removal from the blood (31).…”

Low‐carbohydrate (low & high‐fat) versus high‐carbohydrate low‐fat diets in the treatment of obesity in adolescents

“…There were no significant differences in the changes of any of these parameters among the three groups throughout the study. This finding is in line with other studies of low carbohydrate diets in youth (14–16) and adults (1,4,6). In the randomized controlled trial of Sondike et al (15) in youth, the low carbohydrate group showed a significant decrease in triglyceride level, although the difference among the groups did not reach statistical significance.…”

“…Mean Fat percentage was still lower as compared to baseline values. Our results are in line with several methodic reviews of studies done in adults (1,4,6). In one of the few randomized studies in youth that included a control group, Sondike et al (14) found an advantage for the low‐carbohydrate diet (20–40 g/day) over the low‐fat diet in both weight loss and decrease in BMI.…”

Carbohydrate versus Energy Restriction: Effects on Weight Loss, Body Composition and Metabolism

“…2 a). Our results are consistent with those of Bravata et al [5] , whose meta-analysis of literature concerning Average serum insulin, leptin, and IGF-1 for each diet group at sacrifice. Average serum leptin ( a ) (n = 17 for PF, n = 16 for HC, HF, LC and DER) , insulin ( b ) (n = 17 for HF, n = 16 for PF, n = 14 for LC, n = 12 for HC and n = 11 for DER), and IGF-1 ( c ) (n = 11 for DER, n = 9 for LC, n = 8 for HC, n = 7 for HF and n = 6 for PF).…”

“…In contrast, carbohydrate restriction had little effect on any of these parameters, with the exceptions of glucose and insulin, when compared to the HF group. This study replicates clinical studies in humans [5] , agrees with previous rodent studies [9,21,22] , and provides further evidence that a negative energy balance is critical for reducing weight and reversing obesity-related metabolic changes.…”

Low-Fat Versus Low-Carbohydrate Weight Reduction Diets

“…In contrast to the lack of a change in LDL and HDL in response to the low-carbohydrate diet, there was a significant reduction in triglycerides within this group compared with no significant change within the low-fat group. This response has been consistently reported in other studies comparing a low-carbohydrate and low-fat weight reduction diet (12). It has been speculated that this result is due to a combination of a decrease in the VLDL production rate and an increase in triglyceride removal from the blood (31).…”

Low‐carbohydrate (low & high‐fat) versus high‐carbohydrate low‐fat diets in the treatment of obesity in adolescents

“…There were no significant differences in the changes of any of these parameters among the three groups throughout the study. This finding is in line with other studies of low carbohydrate diets in youth (14–16) and adults (1,4,6). In the randomized controlled trial of Sondike et al (15) in youth, the low carbohydrate group showed a significant decrease in triglyceride level, although the difference among the groups did not reach statistical significance.…”

“…Mean Fat percentage was still lower as compared to baseline values. Our results are in line with several methodic reviews of studies done in adults (1,4,6). In one of the few randomized studies in youth that included a control group, Sondike et al (14) found an advantage for the low‐carbohydrate diet (20–40 g/day) over the low‐fat diet in both weight loss and decrease in BMI.…”

Carbohydrate versus Energy Restriction: Effects on Weight Loss, Body Composition and Metabolism

“…2 a). Our results are consistent with those of Bravata et al [5] , whose meta-analysis of literature concerning Average serum insulin, leptin, and IGF-1 for each diet group at sacrifice. Average serum leptin ( a ) (n = 17 for PF, n = 16 for HC, HF, LC and DER) , insulin ( b ) (n = 17 for HF, n = 16 for PF, n = 14 for LC, n = 12 for HC and n = 11 for DER), and IGF-1 ( c ) (n = 11 for DER, n = 9 for LC, n = 8 for HC, n = 7 for HF and n = 6 for PF).…”

“…In contrast, carbohydrate restriction had little effect on any of these parameters, with the exceptions of glucose and insulin, when compared to the HF group. This study replicates clinical studies in humans [5] , agrees with previous rodent studies [9,21,22] , and provides further evidence that a negative energy balance is critical for reducing weight and reversing obesity-related metabolic changes.…”

Low-Fat Versus Low-Carbohydrate Weight Reduction Diets

“…In contrast to the lack of a change in LDL and HDL in response to the low-carbohydrate diet, there was a significant reduction in triglycerides within this group compared with no significant change within the low-fat group. This response has been consistently reported in other studies comparing a low-carbohydrate and low-fat weight reduction diet (12). It has been speculated that this result is due to a combination of a decrease in the VLDL production rate and an increase in triglyceride removal from the blood (31).…”