A Systematic Review and Meta‐Analysis Comparing Heterogeneity in Body Mass Responses Between Low‐Carbohydrate and Low‐Fat Diets

Abstract Objectives As the never-ending macronutrient debate for weight loss continues, conflicting evidence persist. Per the carbohydrate-insulin hypothesis, a low-carbohydrate diet (LC) should produce a greater weight/fat loss compared to a low-fat/calorie diet (LF) by releasing less of the anabolic hormone insulin. However, from a ‘calories in, calories out’ perspective, does restricting calories on a LC diet produce a greater weight/fat loss compared to a LF diet? Methods A systematic review and meta-analysis of LC vs LF trials for weight loss was conducted and data were collected from 53 studies. Weight loss data were converted to kcals (1 kg = 3500 kcals) and a ratio was produced for each individual diet (ID-Ratio: weight loss in kcals/restricted dietary kcals) where a ratio of 1 indicates that one dietary kcal restriction equals one kcal of weight loss. Next, to compare the two diets, a comparison ratio (DC-Ratio: LC ID-Ration/LF ID-Ratio) was produced where a ratio greater than 1 indicates greater weight loss per dietary calorie restricted with LC diet. These calculations were repeated for body fat loss for full duration (n = 30 trials) and time of greatest weight loss (TGWL; Weight Loss: n = 19 trials; Fat Mass Loss: n = 4 trials). Results LC diets produced a greater weight loss (Full Duration: 6.10 kg vs 4.86 kg; n = 53 trials; P = 0.024; TGWL: 6.29 kg vs 4.34 kg; n = 19 trials; P = 0.024), however no difference was found for the amount of restricted calories or fat mass loss for either duration. No difference was found for the LC and LF ID-Ratios for weight or fat mass loss for either duration. The mean weight loss DC-Ratio was greater than 1 (Full Duration Mean: 1.61, SD: 1.71, n = 53 studies, P = 0.004; TGWL Mean: 1.74, SD: 1.0, n = 19 trails, P = 0.010) indicating a greater weight loss per calorie restricted with a LC diet. However, the fat loss DC-Ratio was not different from 1 (Full Duration Mean: 1.74, SD: 1.09, n = 30 trials, P = 0.552; TGWL Mean: 1.25, SD: 0.53, n = 4 trials, P = 0.428). Conclusions From a ‘calories in, calories out’ perspective, restricting calories on a LC diet produced a greater weight loss for the full duration of the trails and at the time of greatest weight loss compared to a LF diet. As no effect was seen on LC diets and fat mass loss, these results do not support the carbohydrate-insulin hypothesis of obesity. Funding Sources School of Life Sciences, Arizona State University.

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Dietary Intervention for Overweight and Obese Adults: Comparison of Low-Carbohydrate and Low-Fat Diets. A Meta-Analysis

PLoS ONE ◽

10.1371/journal.pone.0139817 ◽

2015 ◽

Vol 10 (10) ◽

pp. e0139817 ◽

Cited By ~ 81

Author(s):

Jonathan Sackner-Bernstein ◽

David Kanter ◽

Sanjay Kaul

Keyword(s):

Dietary Intervention ◽

Meta Analysis ◽

Low Fat ◽

Obese Adults ◽

Low Carbohydrate ◽

Fat Diets

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Long-term effects of low-fat diets either low or high in protein on cardiovascular and metabolic risk factors: a systematic review and meta-analysis

Nutrition Journal ◽

10.1186/1475-2891-12-48 ◽

2013 ◽

Vol 12 (1) ◽

Cited By ~ 97

Author(s):

Lukas Schwingshackl ◽

Georg Hoffmann

Keyword(s):

Risk Factors ◽

Systematic Review ◽

Meta Analysis ◽

Metabolic Risk Factors ◽

Metabolic Risk ◽

Long Term Effects ◽

Low Fat ◽

Fat Diets

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Abstract MP63: Randomized Trials of Low-Fat vs. Other Diet Interventions on Weight Loss: A Meta-Analysis

Circulation ◽

10.1161/circ.129.suppl_1.mp63 ◽

2014 ◽

Vol 129 (suppl_1) ◽

Author(s):

Deirdre K Tobias ◽

Mu Chen ◽

Walter Willett ◽

Frank B Hu

Keyword(s):

Weight Loss ◽

Randomized Trials ◽

Dietary Intervention ◽

Meta Analysis ◽

Dietary Interventions ◽

Low Fat ◽

Intervention Intensity ◽

Low Carbohydrate ◽

Fat Diets

Introduction: The effectiveness of low-fat diets for weight loss has been debated for decades. Dozens of randomized control trials (RCTs) have assessed whether decreasing the intake of total fat leads to weight loss, giving mixed results. Hypothesis: We hypothesized that low-fat dietary interventions do not lead to greater weight loss when comparator diet intervention intensity is considered. Methods: We conducted a systematic review and meta-analysis. RCTs were included if they compared a low-fat dietary intervention to any control diet with at least 1 year of follow-up. We estimated the combined fixed effect inverse variance weighted mean difference of low-fat vs. comparison diets. Several a priori stratified analyses were considered to explore heterogeneity. Results: Fifty studies met inclusion criteria, reporting 1-10 years of follow-up on 70,054 participants. Overall, low-fat dietary interventions resulted in 0.51kg greater weight loss compared to other diets (95% CI = -0.62, -0.40, p<0.001; I2 = 83%). However, when trials where greater attention was given to the low-fat group were excluded, comparator diets led to greater weight loss than low-fat diets (n=30; WMD=0.87, 95% CI=0.56, 1.17, p<0.001). Similarly, when the type of comparator diet was considered, low-fat diets were only beneficial compared to control groups who were simply asked to maintain their usual diet (n=18; WMD = -1.03, 95% CI = -1.18, -0.88, p<0.001). When equal attention was given to intervention groups, low-carbohydrate diets (n=15; WMD = 1.13kg, 95% CI = 0.53, 1.73, p<0.001) and other “healthy” diets without a low-fat component (n=20; WMD = 0.77kg, 95% CI = 0.42, 1.13, p<0.001) led to greater weight loss than low-fat diets. Comparison diets, irrespective of type, were associated with 1.30kg greater weight loss than low-fat diets when the interventions were intended to be isocaloric (n=19; 95% CI = 0.92, 1.69, p<0.001). Conclusions: Low-fat dietary interventions are not more effective than other diets for weight loss when differences in intervention intensity between treatment groups are considered. Rather, evidence from long-term (>=1 year) randomized trials indicates low-carbohydrate or other healthful dietary pattern interventions without a low-fat focus may be more effective for weight loss than low-fat dietary interventions. Further evidence is needed to establish the role of these interventions in longer-term weight loss and weight maintenance.

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The Effect of Low-Fat and Low-Carbohydrate Diets on Weight Loss and Lipid Levels: A Systematic Review and Meta-Analysis

Nutrients ◽

10.3390/nu12123774 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3774

Author(s):

Shreya Chawla ◽

Fernanda Tessarolo Silva ◽

Sofia Amaral Medeiros ◽

Rania A. Mekary ◽

Dina Radenkovic

Keyword(s):

Weight Loss ◽

Total Cholesterol ◽

Meta Analysis ◽

Density Lipoprotein ◽

Lipoprotein Cholesterol ◽

Average Weight ◽

Low Fat ◽

Low Carbohydrate Diet ◽

Low Carbohydrate ◽

Fat Diets

Background: The rise in obesity has emphasised a focus on lifestyle and dietary habits. We aimed to address the debate between low-carbohydrate and low-fat diets and compare their effects on body weight, low-density lipoprotein cholesterol (LDL), high-density lipoprotein cholesterol (HDL), total cholesterol, and triglycerides in an adult population. Method: Medline and Web of Science were searched for randomised controlled trials (RCTs) comparing low-fat and low-carbohydrate diets up to September 2019. Three independent reviewers extracted data. Risk of bias was assessed using the Cochrane tool. The meta-analysis was stratified by follow-up time using the random-effects models. Results: This meta-analysis of 38 studies assessed a total of 6499 adults. At 6–12 months, pooled analyses of mean differences of low-carbohydrate vs. low-fat diets favoured the low-carbohydrate diet for average weight change (mean difference −1.30 kg; 95% CI −2.02 to −0.57), HDL (0.05 mmol/L; 95% CI 0.03 to 0.08), and triglycerides (TG) (−0.10 mmol/L; −0.16 to −0.04), and favoured the low-fat diet for LDL (0.07 mmol/L; 95% CI 0.02 to 0.12) and total cholesterol (0.10 mmol/L; 95% CI 0.02 to 0.18). Conclusion and Relevance: This meta-analysis suggests that low-carbohydrate diets are effective at improving weight loss, HDL and TG lipid profiles. However, this must be balanced with potential consequences of raised LDL and total cholesterol in the long-term.

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Effects of macronutrient intake in obesity: a meta-analysis of low-carbohydrate and low-fat diets on markers of the metabolic syndrome

Nutrition Reviews ◽

10.1093/nutrit/nuaa044 ◽

2020 ◽

Author(s):

Anouk E M Willems ◽

Martina Sura–de Jong ◽

André P van Beek ◽

Esther Nederhof ◽

Gertjan van Dijk

Keyword(s):

Metabolic Syndrome ◽

Weight Loss ◽

Meta Analysis ◽

Caloric Intake ◽

Macronutrient Intake ◽

Fat Intake ◽

Low Fat ◽

The Metabolic Syndrome ◽

Low Carbohydrate ◽

Fat Diets

Abstract The metabolic syndrome (MetS) comprises cardiometabolic risk factors frequently found in individuals with obesity. Guidelines to prevent or reverse MetS suggest limiting fat intake, however, lowering carbohydrate intake has gained attention too. The aim for this review was to determine to what extent either weight loss, reduction in caloric intake, or changes in macronutrient intake contribute to improvement in markers of MetS in persons with obesity without cardiometabolic disease. A meta-analysis was performed across a spectrum of studies applying low-carbohydrate (LC) and low-fat (LF) diets. PubMed searches yielded 17 articles describing 12 separate intervention studies assessing changes in MetS markers of persons with obesity assigned to LC (<40% energy from carbohydrates) or LF (<30% energy from fat) diets. Both diets could lead to weight loss and improve markers of MetS. Meta-regression revealed that weight loss most efficaciously reduced fasting glucose levels independent of macronutrient intake at the end of the study. Actual carbohydrate intake and actual fat intake at the end of the study, but not the percent changes in intake of these macronutrients, improved diastolic blood pressure and circulating triglyceride levels, without an effect of weight loss. The homeostatic model assessment of insulin resistance improved with both diets, whereas high-density lipoprotein cholesterol only improved in the LC diet, both irrespective of aforementioned factors. Remarkably, changes in caloric intake did not play a primary role in altering MetS markers. Taken together, these data suggest that, beyond the general effects of the LC and LF diet categories to improve MetS markers, there are also specific roles for weight loss, LC and HF intake, but not reduced caloric intake, that improve markers of MetS irrespective of diet categorization. On the basis of the results from this meta-analysis, guidelines to prevent MetS may need to be re-evaluated.

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Very-low-energy diets and morbidity: a systematic review of longer-term evidence

British Journal Of Nutrition ◽

10.1017/s0007114512001924 ◽

2012 ◽

Vol 108 (5) ◽

pp. 832-851 ◽

Cited By ~ 24

Author(s):

Y. Mulholland ◽

E. Nicokavoura ◽

J. Broom ◽

C. Rolland

Keyword(s):

Systematic Review ◽

Weight Loss ◽

Best Practice ◽

Low Energy ◽

Current Evidence ◽

Behaviour Therapy ◽

Low Fat ◽

Target Weight ◽

Low Carbohydrate ◽

Fat Diets

Evidence from the literature supports the safe use of very-low-energy diets (VLED) for up to 3 months in supervised conditions for patients who fail to meet a target weight loss using a standard low-fat, reduced-energy approach. There is, however, a need for longer-term outcomes on obesity and associated morbidities following a VLED. The present systematic review aims to investigate longer-term outcomes from studies using VLED, with a minimum duration of 12 months, published between January 2000 and December 2010. Studies conducted in both children and adults, with a mean/median BMI of ≥ 28 kg/m2 were included. PubMed, MEDLINE, Web of Science and Science Direct were searched. Reference lists of studies and reviews were manually searched. Weight loss or prevention of weight gain and morbidities were the main outcomes assessed. A total of thirty-two out of 894 articles met the inclusion criteria. The duration of the studies ranged from 12 months to 5 years. Periods of VLED ranged from 25 d to 9 months. Several studies incorporated aspects of behaviour therapy, exercise, low-fat diets, low-carbohydrate diets or medication. Current evidence demonstrates significant weight loss and improvements in blood pressure, waist circumference and lipid profile in the longer term following a VLED. Interpretation of the results, however, was restricted and conclusions with which to guide best practice are limited due to heterogeneity between the studies. The present review clearly identifies the need for more evidence and standardised studies to assess the longer-term benefits from weight loss achieved using VLED.

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