Cooking with some vegetable oils rather than saturated fats may not improve heart health, researchers claim today.
The use of oils rich in linoleic acid may reduce cholesterol levels – but does not impact on mortality rates, according to the new analysis.
Researchers took a closer look at the "traditional diet-heart hypothesis" that replacing saturated fat with vegetable oils will reduce an individual’s cardiovascular risk by lowering cholesterol.
Linoleic acid is associated with omega-6 fatty acids and is found in high levels in sunflower oil and corn oil and in lower levels in rapeseed oil, palm oil and olive oil.
Dr Christopher Ramsden of the University of North Carolina, USA, and colleagues write in today’s (13 April) BMJ that: "This paradigm has never been causally demonstrated in a randomised controlled trial and thus has remained uncertain for over 50 years."
The team re-analysed unpublished information from the Minnesota Coronary Experiment, set in 1968-73, which tested the replacement of saturated fat with vegetable oil rich in linoleic acid on 9,423 women and men aged 20 to 97 years. They also carried out a review of several similar trials.
The Minnesota study used a vegetable oil and margarines made from maize.
Although the vegetable oil group had lower cholesterol levels, there was "no mortality benefit", in fact this group had a higher risk of death proportional to their lower cholesterol.
In five further trials with 10,808 participants, "cholesterol lowering interventions showed no evidence of benefit on mortality from coronary heart disease or all causes".
The authors point out that, although small amounts of linoleic acid are essential for health, high intakes are not natural to human diets, and preliminary evidence links by-products of linoleic acid to chronic pain and other diseases.
"Incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid," they conclude.
Professor Jeremy Pearson of the British Heart Foundation commented: “This is an interesting study which shows that decreasing your intake of saturated fat can have a positive impact in helping lower cholesterol. More research and longer studies are needed to assess whether or not eating less saturated fat can reduce your risk of cardiovascular death."
Ramsden, C. E. et al. Re-evaluation of traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73). BMJ 13 April 2016; doi: 10.1136/bmj.i1246 [abstract]
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