12 January - 20 June 2016

Re-evaluating replacing saturated fat with vegetable oil high in linoleic acid

The traditional diet-heart hypothesis has been to replace saturated fat with vegetable oil rich in linoleic acid in order to reduce serum cholesterol and subsequently reduce cardiovascular disease and death. A study published in the British Medical Journal has re-evaluated this and its findings suggest that replacement of saturated fat may lower serum cholesterol but does not lower risk of death from coronary heart disease or all cause.

The traditional diet-heart hypothesis has been to replace saturated fat with vegetable oil rich in linoleic acid in order to reduce serum cholesterol and subsequently reduce cardiovascular disease and death.  A study published in the British Medical Journal has re-evaluated this and its findings suggest that replacement of saturated fat may lower serum cholesterol but does not lower risk of death from coronary heart disease or all cause.

The highly cited study by Ramsden et al. analysed unpublished and published data from the Minnesota Coronary Experiment (MCE), a double blinded, parallel group, randomised controlled trial conducted in 1968-73, and involving 9570 participants aged 20-97, recruited from a nursing home and 6 hospitals.  The MCE investigated the effect of increasing n-6 linoleic acid from corn oil in place of saturated fat and lasted from 41 to 56 months.

The participants were randomly assigned to consume either a diet that was low in saturated fat (reduced by 50% from baseline hospital diet, 18.5% to 9.2% calories), but high in linoleic acid-rich vegetable oil (increased by more than 280%, from about 3.4% to 12.2% of calories), or a control diet that had the same amount of saturated fat used before the study, but with an increase in linoleic acid (by about 38% , from 3.4% to 4.7% of calories).

Ramsden et al. analysed available serum cholesterol levels data from a subgroup of 2355 participants who had followed the diet for a year or more.  The participants had an average of six follow-up measurements.  The researchers took into account confounding factors such as baseline cholesterol, age, sex, BMI, blood pressure and adherence to the diet. 

Ramsden et al. then performed a systematic review and meta-analysis of any randomised controlled trial that compared diets using vegetable oil in place of saturated fat and no other intervention. The team identified 5 randomised controlled trials for inclusion, involving 10808 participants in total. 

The scientists report that the participants on the intervention diet had significantly lower levels of cholesterol compared with the control group and baseline (13.8% compared to the control diet, which lowered cholesterol by just 1%).  In both groups, for each 0.78mm/l reduction in serum cholesterol, there was a 22% higher risk of death from any cause.  This appeared to be driven by a 35% higher risk for 595 people aged 65 years or more at the start of the study.  Based on 149 deaths, there was no association between cholesterol reduction and death for the 1,760 people aged under 65.   

The systematic review found no difference between the diets, substituting saturated fats with vegetable oils rich in linoleic acid, in terms of death from coronary heart disease. 

In conclusion the scientists state that whiles the replacement of saturated fat with linoleic acid effectively lowers serum cholesterol it does not support the hypothesis “that this translates to a lower risk of death from coronary heart diseases or all causes.”

RSSL has expertise in all aspects of fat analysis and fatty acid profiling including the determination of CLA.  For more information please contact Customer Services on +44 (0) 118 918 4076 or email enquiries@rssl.com 

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