Abstract
Background: Increasing sugars intakes has been linked to an increased risk of cardiovascular disease such as diabetes, insulin resistance and obesity. When sugars are consumed in excess of energy requirements and glycogen storage capacity they are converted to lipids in the liver and stored as fat. This also results in an increase in circulating lipid concentrations in the blood. The aim of this thesis was to determine whether there is a relationship between consumption of dietary sugars and blood lipids as a biomarker of cardiovascular risk.
Design: Systematic review and meta-analysis of randomised controlled trials (RCTs) following the Cochrane Collaboration guidelines including and using Cochrane meta-analysis software Revman 5.0.
Data sources: Four article databases (OVID Medline, Scopus, Embase and CINAHL) were searched for randomised controlled trials published before April 2012. Grey literature sources and references lists of review articles were also searched.
Study selection: We included randomised controlled trials from 1960 to the present, where dietary sugars intake was increased in one arm of the study in comparison with another and which reported effects on one of the following outcome measures; triglycerides, HDL, LDL or total cholesterol. Participants were healthy subjects who were not affected by a metabolism-altering disease and were not undergoing any acute treatment for disease.
Data synthesis: Mean pooled effects of higher versus lower sugars intakes on lipid outcome measures were estimated using inverse variance models of analysis with random effects to account for heterogeneity. Subgroup analyses further examined the effects of study length, study type, provision of intervention, type of intervention, type of control group, weight loss and diabetes on the association between sugars intake and lipids.
Results: 17,020 potentially relevant studies were identified by electronic searches. 35 studies remained after deduplication and exclusion of studies that did not meet the inclusion criteria. 873 participants participating in 10 parallel trials and 25 crossover trials were included. Higher compared with lower sugars intakes was associated with raised triglycerides (0.13mmol/L [95% confidence interval (CI) = 0.07, 0.20]), LDL cholesterol (0.20mmol/L [95% CI = 0.07, 0.33]) and total cholesterol (0.07mmol/L [95% CI = 0.03, 0.10]). There was no significant association with HDL cholesterol. Weight increase in those with a high dietary sugar intake was associated with a significant decrease in total cholesterol in contrast with no weight change, which was associated with an increase in total cholesterol. The effects of sugars in lipids were strengthened in crossover trials, those trials where dietary intake was isoenergetic and in interventions where sugars were exchanged for complex carbohydrates rather than other simple carbohydrates. Accounting for potential bias attenuated the findings somewhat.
Conclusions: This meta-analysis provides evidence that high dietary sugars intake is a determinant of raised lipid biomarkers of cardiovascular disease, indicating increased risk.