The Facts on Natural Trans Fats and Cardiovascular Disease
It is well established that industrial trans fats increase the risk of cardiovascular disease. The effects of natural trans fats, particularly ruminant fats, are less clear. Current evidence suggests that ruminant trans fats are not associated with an increased risk of cardiovascular disease. In fact, emerging evidence suggests a beneficial effect of specific ruminant trans fatty acids on cardiovascular health.
Current dietary guidelines recommend restricting trans fats intake to reduce cardiovascular risk. However, while industrial trans fats increase the risk of cardiovascular disease, natural trans fats, such as ruminant trans fats, have a different bioactivity and may be associated with cardiovascular health benefits.1
A 2014 systematic review and meta-regression of clinical trials was conducted by Gayet-Boyer et al. to investigate the relationship between ruminant trans fat and cardiovascular risk markers. The analysis consisted of 13 studies and 666 healthy adults.2
- Ruminant trans fat was not associated with a change in the ratio of total cholesterol to LDL cholesterol;
- Ruminant trans fat was not associated with a change in the ratio of LDL cholesterol to HDL cholesterol;
- The authors concluded that current average intake (~4.2% of daily energy intake) of ruminant trans fat has no harmful effects on key cardiovascular risk markers, including the ratio of total cholesterol to LDL cholesterol and the ratio of LDL cholesterol to HDL cholesterol.
In their 2011 systematic review and meta-analysis of cohort studies, Bendsen et al. assessed the association between the intake of trans fatty acids and the risk of coronary heart disease. There was no significant association between the intake of ruminant trans fatty acids and the risk of coronary heart disease.3
- The pooled relative risk estimates of the extreme quintiles of total trans fatty acid intake, which corresponded to increments ranging from 2.8 to ~ 10 g/day, were 1.22 (95% CI: 1.08-1.38, p = 0.002) for coronary heart disease events and 1.24 (95% CI: 1.07-1.43, p = 0.003) for fatal coronary heart disease;
- The risk ratio for the association between increments of ruminant trans fatty acids, ranging from 0.5 to 1.9 g/day, and the risk of coronary heart disease was 0.92 (95% CI: 0.76-1.11, p = 0.36);
- The analysis suggested that industrial trans fatty acids may be positively related to coronary heart disease;
- There were no definite conclusions regarding the importance of the source of trans fatty acids owing to the limited number of studies.
A narrative review published in 2011 examined the evidence from epidemiological and clinical studies to determine whether the intake of specific ruminant trans fatty acids has an effect on cardiovascular disease compared to industrial trans fatty acids:4
- It is difficult to consume very high amounts of ruminant trans fatty acids in a typical diet;
- Epidemiological studies have generally shown that there is an inverse association or no association between ruminant trans fatty acid intake and coronary heart disease across multiple geographical locations;
- A double-blind, randomized, crossover controlled trial found that moderate doses of ruminant trans fatty acids, which would be potentially attainable with the consumption of a very high-dairy diet, do not affect lipids and lipoproteins in healthy individuals;
- High doses of ruminant trans fatty acids, which are not attainable by diet, may have similar effects as industrial trans fatty acids.
Another 2011 narrative review reports that dietary intakes of trans fatty acids from milk and milk products are far from being high enough to constitute a serious threat for public health.5
Furthermore, in the World Health Organization scientific review on trans fatty acids, it is indicated that:6
- There is no conclusive evidence supporting an association between the amounts of ruminant trans fatty acids that are usually consumed and the risk for cardiovascular disease;
- Conversely, industrial trans fatty acids from the partial hydrogenation of fats and oils have no demonstrable health benefits and pose clear risks to human health.
The mechanisms by which ruminant trans fats may affect cardiovascular health are not clear.
There is evidence from human studies and animal models to suggest that ruminant trans fatty acids may improve blood lipid profiles and decrease cholesterol absorption.7,8
CLA and vaccenic acid may play a particularly important role in the underlying mechanistic cardiovascular effects of ruminant trans fatty acids.9
CLA has been shown to be an agonist of the peroxisome proliferator-activated receptor (PPAR) pathway and to modulate the expression of PPAR-γ. This helps to normalize insulin sensitivity, improve lipid metabolism and lipoprotein clearance, and restore vascular contractility and endothelial function. CLA may also increase the expression of hepatic lipoprotein receptors.2
It has also been suggested that vaccenic acid may modulate eicosanoid production to regulate metabolic pathways involved in atherogenesis, such as lipid metabolism, immune response, vascular function and platelet aggregation.4
Furthermore, the intake of ruminant trans fats may decrease body weight and reduce fat deposition.10
The intake of ruminant trans fatty acids is not associated with an increased risk of cardiovascular disease. In addition, the amount of trans fatty acids in milk and milk products is not harmful to cardiovascular health.
More research is needed for definitive answers on the effect of ruminant trans fats and the risk of cardiovascular disease, and more studies are required to investigate individual ruminant trans fatty acids and their mechanisms.
- Wang Y and Proctor SD. Current issues surrounding the definition of trans-fatty acids: implications for health, industry and food labels. Br J Nutr 2013;110:1369-1383.
- Gayet-Boyer C et al. Is there a linear relationship between the dose of ruminant trans-fatty acids and cardiovascular risk markers in healthy subjects: results from a systematic review and meta-regression of randomised clinical trials. Br J Nutr 2014;112:1914-1922.
- Bendsen NT et al. 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;65:773-783.
- Gebauer SK et al. Effects of ruminant trans fatty acids on cardiovascular disease and cancer: a comprehensive review of epidemiological, clinical, and mechanistic studies. Adv Nutr 2011;2:332-354.
- Tardy AL et al. Ruminant and industrial sources of trans-fat and cardiovascular and diabetic diseases. Nutr Res Rev 2011;24:111-117.
- Uauy R et al. WHO Scientific Update on trans fatty acids: summary and conclusions. Eur J Clin Nutr 2009;63:S68-S75.
- Rice BH et al. Ruminant-produced trans-fatty acids raise plasma HDL particle concentrations in intact and ovariectomized female hartley guinea pigs. J Nutr 2012;142:1679-1683.
- Labonté MÈ et al. Comparison of the impact of trans fatty acids from ruminant and industrial sources on surrogate markers of cholesterol homeostasis in healthy men. Mol Nutr Food Res 2011;55:S241-S247.
- Wang Y et al. The role of ruminant trans fat as a potential nutraceutical in the prevention of cardiovascular disease. Food Res Int 2012;46:460-468.
- Hansen CP et al. Intake of ruminant trans fatty acids and changes in body weight and waist circumference. Eur J Clin Nutr 2012;66:1104-1109.