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Trans Fats and Cardiovascular Disease: New Findings

Having demonstrated that hydrogenated vegetable oil (i.e., trans fat from industrial sources or iTFA) is bad from the standpoint of cardiovascular health,¹ scientists are facing a new challenge: what is the impact of natural trans fat?

Background

Trans fat from natural sources may represent as much as 20% of all dietary trans fat consumed by North Americans.² The main sources of natural trans fat are dairy products and meat from ruminants, often referred to as trans fat from ruminants (rTFA). There are notable differences between iTFA and rTFA.

More than 50% of industrial fats have a trans configuration, whereas in milk fat, trans fatty acids represent only 5% of the total fat, and vaccenic acid (18:1t-11) is the prominent isomer. Based on the available prospective cohort studies, rTFA, unlike iTFA, does not appear to be associated with an increased risk of cardiovascular disease (CVD),^3-5 but these data require further substantiation through clinical studies.

Percent change in lipid risk factors from the control diet low in trans fat (TFA) from any source. rTFA: trans fat from ruminants; iTFA: trans fat from industrial sources

Our study

In 2008, we conducted a double-blind, randomized, placebo-controlled, crossover study to compare the impact of iTFA and rTFA on a series of risk factors for CVD.⁶ A total of 38 healthy men were assigned to each of 4 experimental isoenergetic diets lasting 4 weeks each. All diets were identical in terms of macro- and micronutrients, with the exception of trans fat, which varied by source and quantity as follows:

• High rTFA (3.7% of daily energy; equivalent to daily consumption of 10 servings of cheese, 5 servings of whole milk, 2 servings of full-fat yogurt and 20 teaspoons of butter);
• Moderate rTFA (1.5% of energy; equivalent to daily consumption of 4 servings of cheese, 2 servings of whole milk, 1 serving of full-fat yogurt and 8 teaspoons of butter);
• High iTFA (3.7% of energy);
• Control diet low in TFA from any sources (0.8% of energy).

While it is easy to achieve a high dietary intake of iTFA as tested here, it is virtually impossible to achieve a high level of rTFA with typical human consumption.

Results

• Plasma LDL cholesterol (LDL-C) concentrations were higher after the high rTFA diet than after the control diet (p=0.03) and the moderate rTFA diet (p=0.002);
• Plasma LDL-C concentrations were also higher after the high iTFA diet than after the moderate rTFA diet (p=0.02);
• The moderate rTFA diet was associated with the most favourable lipid values, although these did not reach statistical significance when compared to the control diet;
• There were no differences between each of the 4 diets in terms of other CVD risk factors.

Highlights

A moderate (but still greater than average) intake of rTFA does not have an adverse effect on plasma lipids and other cardiovascular risk factors.

Very high intakes of natural trans fat (>3.5% of energy intake) appear to have an unfavourable effect on blood cholesterol. However, the intakes of rTFA in this study were substantially higher than could possibly be achieved in a normal human diet.

Dietary trans fat from ruminants is unlikely to contribute to the risk of CVD.

Keywords: trans fat

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