Research commentary
Effects of macronutrient intake in obesity: a meta-analysis of low-carbohydrate and low-fat diets on markers of the metabolic syndrome
Anouk E M Willems, Martina Sura–de Jong, André P van Beek, Esther Nederhof, Gertjan van Dijk
Nutrition Reviews, nuaa044, https://doi.org/10.1093/nutrit/nuaa044
Published: 04 September 2020
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.1
Comment
This was an interesting study because the authors chose to mostly look at the data as a continuum of macronutrients, rather than simply comparing the two types of diets. In other words, the actual doses of carbohydrate and other macronutrients were compared across all studies in a linear regression analysis. This provides a unique insight into how actual intakes of macronutrients might affect cardiometabolic outcomes.
Some of the key points of interest were:
- Reducing carbohydrate was associated with weight loss with ~6-11% reduction in carbohydrate (as % of total energy) related to a 1 kg weight loss.
- Conversely, ~6-9% increase in fat intake was associated with 1 kg weight loss.
- Protein had the strongest effect with a 2-3% increase in protein associated with a 1 kg weight loss.
Note: Actual fibre intake, percent changes in macronutrient and saturated fat intake from baseline nor the absolute change in fibre intake were correlated with body weight loss at 6 and 12 months.
- Every 1 mmHg lowering in diastolic blood pressure was related to a 7.4% increase in fat intake and with 10.8% reduction in carbohydrate intake
- Every 1 mmol/L lowering in TAG levels related with 55.6% increase in actual fat intake and with 83.3% reduction in actual carbohydrate intake
These findings suggest that reducing the carbohydrate content of the diet, and increasing protein and fat, results in improved measures of cardiometabolic health, including weight, HDL cholesterol, diastolic blood pressure, and triglycerides.
Reference
1. Willems AEM, Sura–de Jong M, van Beek AP, Nederhof E, van Dijk G. Effects of macronutrient intake in obesity: a meta-analysis of low-carbohydrate and low-fat diets on markers of the metabolic syndrome. Nutrition reviews. 2020.
