Effects of fructose consumption on postprandial TAG: an update on systematic reviews with meta-analysis

Br J Nutr. 2018 Aug; 120(4):364-372. doi: 10.1017/S0007114518001538  — Macedo RCO, Vieira AF, Moritz CEJ, and Reischak-Oliveira A. — Download PDF

Objective:

  • To re-examine the chronic effect (>7 days) of fructose consumption on postprandial TAG, in adolescents and adults.

Background:

  • Exaggerated elevation of TAG in the postprandial period represents an abnormal metabolism response and is associated with increased morbidity and mortality as a result of reduced insulin sensitivity and endothelial dysfunction due to oxidative stress.
  • Several studies have shown the effect of fructose-rich diets on postprandial TAG increase. The mechanism appears to be associated with the stimulation of liver lipogenesis, reduced insulin sensitivity and secretion or reduction of VLDL-TAG clearance. As a result of this association with atherogenic lipids and lipoproteins, it is suggested that fructose has an indirect role in increased CVD risk.
  • Though the effects of fructose consumption on fasting and postprandial TAG (in acute and chronic forms) have been previously analyzed by systematic reviews with meta-analyses, the authors of the present studysuggest that investigators of two of the previous reviews declared “important conflicts of interest stemming from food industry funding”.
  • The authors state that the reporting of negative effects only when it contributes to an excess of energy in the diet by industry-funded reviews warrant the re-examination of these affects.

Methods:

  • This review considered human trials that evaluated the effect of fructose consumption over a period of > 7 days. The comparison of the intervention with any other non-fructose carbohydrate on the variation of postprandial TAG immediately before breakfast and at the 4-hour peak was required.
  • The guidelines presented in Preferred Reporting Items for Systematic Reviews and Meta-Analyses were adhered to for the present study.
  • Following the database search, the removal of duplicates and irrelevant studies, eight studies and 12 interventions were included in the review.
  • Of the twelve included interventions, five included a sample of healthy individuals, four with diabetics, and three with overweight/obese individuals. Most (83.3%) were carried out in a cross-over (83.3%) and randomized (75%) design, and exclusively in an environment external to the laboratory (41.6%). The mean intervention period was 28 days.
  • The amount of fructose provided in the studies had a mean of 92.6g or 20% of the total energy of the diet.

Findings:

  • Compared with other carbohydrates, fructose generated higher variation on the concentration of TAG in the postprandial period.
  • The analysis of subgroups showed higher variation of TAG concentration for overweight/obese and healthy individuals, but not diabetics.
  • The meta-analysis found that quantities smaller than 87g of fructose/day are enough to promote variation in postprandial TAG. This finding was observed in previous meta-analyses which observed a threshold of 50g/day for the general population and 60g/day for type 2 diabetes. However, this effect only occurred when there was a positive energy balance or when fructose is generating a hyperenergetic condition in comparison with another carbohydrate.

Conclusions:

  • The authors concluded that investigators receiving industry funding had the tendency to show no increase in TAG concentration after fructose consumption. Non-randomized interventions, positive energy balance, liquid fructose, glucose comparison component, total intervention period > 30 days (follow-up), and length of analysis > 12 hours influenced the results of the study.
  • As chronic ingestion of fructose may promote lipaemic alterations, and hypertriacylglycerolaemia in the postprandial period is associated with increased morbidity and mortality, recommendations for the population are needed to limit intake, especially from liquids.
  • Well-controlled longitudinal studies (> 30 days), with habitual does of consumption between 49-87g in different forms (free fructose, high-fructose corn syrup, sucrose, etc) are necessary to clarify the interrelationship between fructose, lipaemia and CVD.

Points to Consider:

  • The amount of fructose varied widely among the included studies (50-182g), which illustrates a lack of standardization.
  • ll the interventions that included diabetic samples analyzed plasma TAG over a period of 4 hours, which may represent bias. Studies with longer analysis periods are needed, especially among diabetic subjects.
  • The quality of studies varied widely between groups, presenting a higher risk of bias in diabetes interventions.
  • The data showed high heterogeneity. Sensitivity analysis demonstrated that this effect was almost exclusively generated by one study, though its removal did not alter the subgroup or meta-analysis results.

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