Physicians' Academy for Cardiovascular Education

Industrial trans fats confer more CV health risks than saturated fats

Literature - De Souza RJ et al., BMJ 2015

Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies


De Souza RJ, Mente A, Maroleanu A et al.
BMJ 2015;351:h3978 DOI: 10.1136/bmj.h3978 (Published 12 August 2015)
 

Background

Existing dietary guidelines on the intake of saturated fats have recently been questioned, while simultaneously, public health efforts to focus on reducing trans fats in the food supply have intensified in several countries.
Modest cardiovascular (CV) benefits of substituting saturated fat intake by polyunsaturated fat have been observed in intervention trials [1], but most of these trials had a maximum duration of 2 years and examined surrogate outcomes. A meta-analysis of randomised trials found a 17% CVD risk reduction in studies that reduced saturated fat intake from approximately 17% to 9% [2].
Trans fats are produced industrially through partial hydrogenation of liquid plant oils or can occur naturally in meat and dairy products. A meta-analysis reported an increased pooled relative risk of CHD when comparing extremes of total intake of trans fats (RR: 1.22, 95%CI: 1.08-1.38, P=0.002), and of industrially produced trans fats (RR: 1.30, 95%CI: 0.80-2.14, P=0.29) and ruminant derived trans fats (RR: 0.93, 95%CI: 0.74-1.18, P=0.56) [3].
This meta-analysis aimed to extend and update previous work to determine prospective associations between these fats and all cause mortality and type 2 diabetes (T2DM), to distinguish estimates for risk of CV morbidity and mortality and to assess the confidence in the observational evidence using the GRADE approach [4-6].
41 Primary reports of prospective cohort studies of associations between saturated fats and health outcomes provided 67 data points for the quantitative synthesis, and 20 reports on the relation between trans fats and health outcomes, providing 28 data points, were included. Highest and lowest intake estimates were compared.
 

Main results (see original article for the details of specific analyses)

  • Most adjusted multivariable risk estimates did not reveal statistically significant associations between intake of saturated fats and all-cause mortality (RR: 0.99, 95%CI: 0.91-1.09, P=0.91), CHD mortality (RR: 1.15, 95%CI: 0.97-1.36, P=0.10), CVD mortality (RR: 0.97, 95%CI: 0.84-1.12, P=0.69) and total CHD (RR: 1.06, 95%CI: 0.95-1.17, P=0.29).
    Neither were significant associations seen for saturated fat consumption and ischaemic stroke and T2DM.
  • A summary most adjusted multivariable elevated risk ratio for total trans fats of 1.34 (95%CI: 1.16-1.56, P<0.001) was seen for all cause mortality, and for CHD mortality of 1.28 (95%CI: 1.09-1.50, P<0.003), and of 1.21 (95%CI: 1.10-1.33, P<0.001) for total CHD.
    No statistically significant association between total trans fat and ischemic stroke was seen, nor with T2DM.
  • Studies specifying the source of trans fats reported a increased risk of CHD mortality and morbidity with high intake of industrially produced trans fats, while no significant associations between ruminant derived trans fats and risk of CHD were described.
  • GRADE evidence profiles showed moderate certainty of the estimates for the association between total trans fats and total CHD and CHD mortality and low or very low for the other estimates of trans fats, and very low for the associations between saturated fats and all outcomes.
 

Conclusion

This study of observational evidence found no clear association between higher intake of saturated fats and all cause mortality, CHD, CHD mortality, ischemic stroke or T2DM in apparently healthy adults. Consumption of trans unsaturated fatty acids, on the other hand, was associated with an increase in all cause mortality, CHD mortality and risk of CHD. Industrial trans fats appear to account for a higher risk of CHD events and CHD mortality, while no such associations were seen for ruminant trans fat.
 
Find this study online at NEJM
 

References

1 Mozaffarian D, Micha R, Wallace S. Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med 2010;7:e1000252.
2 Hooper L, Martin N, Abdelhamid A, Davey Smith G. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev 2015;6:CD011737.
3 Bendsen NT, Christensen R, Bartels EM, Astrup A. Consumption of industrial and ruminant trans fatty acids and risk of coronary heart disease: a systematic review and meta-analysis of cohort studies. Eur J Clin Nutr 2011;65:773-83.
4 Guyatt GH, Oxman AD, Vist GE, et al. GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. BMJ 2008;336:924-6.
5 Guyatt G, Oxman AD, Akl EA, et al. GRADE guidelines: 1. Introduction-GRADE evidence profiles and summary of findings tables. J Clin Epidemiol 2011;64:383-94.
6 Guyatt GH, Oxman AD, Schunemann HJ, et al. GRADE guidelines: a new series of articles in the Journal of Clinical Epidemiology. J Clin Epidemiol 2011;64:380-2.

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