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Dietary fat intake and risk of coronary heart disease

Marianne Uhre Jakobsen

Summary


Background and aims

The mortality from coronary heart disease (CHD) is declining in Denmark, but it is still one   of the leading causes of death. In 2000, a total of 9,111 Danes died from CHD,   corresponding to 16% of all deaths.  

Dietary trials and observational studies have linked the intake of dietary fat to the risk of   CHD but it is still controversial whether dietary prevention of heart disease should focus on   only the quantity of dietary fat or on both the quantity and the quality of dietary fats. The   effect of dietary fat on risk of CHD is at least partially mediated by the effect of dietary fat   on plasma lipids. National health organizations recommend dietary changes that decrease   intake of saturated fatty acids to prevent CHD. The rationale is to reduce the low-density   lipoprotein cholesterol concentration in plasma.  

National health organizations also recommend dietary changes that decrease intake of trans   fatty acids (TFA). TFA are present in margarines, shortenings and frying fats as a result of   industrial partial hydrogenation of unsaturated vegetable oils. Milk fat and meat from   ruminants also contain TFA as a result of bacterial hydrogenation of unsaturated fatty acids   in the rumen. Epidemiological studies have shown a direct association between the intake of   TFA and the risk of CHD, primarily accounted for by industrially produced TFA. In   Denmark, the content of industrially produced TFA in margarines has been reduced and   consequently the intake of industrially produced TFA has decreased. In contrast, a change in   the intake of ruminant TFA can be achieved only by changing the intake of dairy and   ruminant meat products. Thus, a change in the intake of ruminant TFA is a much more   complex issue.

The aims of the present thesis were therefore:  

  1. To assess the variation in intake of ruminant TFA in the Danish population aged 1-80   years in order to establish a basis for a description of the association between the intake   of ruminant TFA and the risk of CHD.  
  2. To describe the associations between the intake of major types of fat (saturated fat,   monounsaturated fat, and polyunsaturated fat) and the risk of CHD.  
  3. To describe the association between the intake of ruminant TFA and the risk of CHD.  

Materials and methods  

The first part of this thesis is based on data from a cross-sectional dietary survey conducted   at the Danish Institute for Food and Veterinary Research, including 3,098 persons aged 1-80   years who provided information on diet using a 7-day food record (study aim 1). The second   part of this thesis is based on data from four cohort studies conducted at the Research Centre   of Prevention and Health, Denmark (study aim 2 and 3). A total of 3,686 persons who   provided information on diet using a 7-day weighed food record were followed for 16 years   (study aim 2) and 18 years (study aim 3). The outcome (study aim 2 and 3) was fatal or nonfatal   CHD events.  

Results  

Study aim 1  
The estimated median intake of ruminant TFA was 1.7 g/day (0.7 percentage of energy   intake (E%)) with the 80% central range being from 0.9 g/day (0.5 E%) to 2.7 g/day (1.0   E%), and dairy products contributing 86% of ruminant TFA intake.  

Study aim 2 and 3
Saturated fat  
The energy intake from saturated fat was directly associated with the risk of CHD among   women, whereas no overall association was found among men. However, age-dependent   analyses among men showed a trend for a direct association between the intake of saturated     fat and the risk of CHD among men less than 60 years but not among men 60 years or more.   The same pattern, and even stronger, was seen among women.  

Monounsaturated fat  
There were no overall associations between the energy intake from monounsaturated fat and   the risk of CHD among neither women nor men. However, age-dependent analyses among   women showed a direct association between the intake of monounsaturated fat and the risk   of CHD among women less than 60 years but not among women 60 years or more. The   same pattern was seen among men.  

Polyunsaturated fat  
There was a trend for an inverse association between the energy intake from   polyunsaturated fat and the risk of CHD among women, and among men 60 years or more.   Among women, for a fixed total energy intake, this trend was stronger when the lower   energy intake was due to a lower energy intake from saturated fat than when the lower   energy intake was due to a lower energy intake from carbohydrates, highlighting the   importance of the quality of dietary fats.  

Trans fatty acids  
The intake of ruminant TFA was not associated with the risk of CHD in multivariate   analysis among neither women nor men. However, after additional adjustment for saturated   fat the absolute intake of ruminant TFA was borderline significantly inversely associated   with the risk of CHD among women but not among men. Likewise, there was a trend for an   inverse association between the energy-adjusted intake of ruminant TFA and the risk of   CHD among women but not among men after additional adjustment for saturated fat.  

Conclusion  

The median intake of ruminant TFA in the Danish population aged 1-80 years is estimated   to be 1.7 g/day (0.7 E%) with the 80% central range being from 0.9 g/day (0.5 E%) to 2.7   g/day (1 E%), and dairy products being the main source of ruminant TFA.     The present results support recommendation of a decrease in the intake of saturated fat in   order to prevent CHD. In addition, the results indicate that an increase in the intake of   polyunsaturated fat may contribute to prevent CHD. Furthermore, the results suggest that   the intake of ruminant TFA is not associated with a higher risk of CHD; a high intake of   TFA from dairy and ruminant meat products may therefore be an issue of no concern in   public health. Whether intake of ruminant TFA is innocuous or even protective against   CHD cannot be concluded from the present thesis. Thus, the present results suggest that   CHD risk relates to both the quantity and the quality of dietary fats rather than only the   quantity of fat.