Replacing saturated fat with veggie oil might not offer life-saving impact once thought, study shows
In fact, the risk of dying from heart disease could increase in some people who make the switch, according to researchers who recently examined unpublished data from randomized controlled trials looking at the impact on heart health of saturated fat and vegetable oil.
Christopher Ramsden at the National Institutes of Health and University of North Carolina recently led a team to reexamine unpublished data recovered from the Minnesota Coronary Experiment that tested in 9,423 participants 45 years ago on whether replacing saturated fat with vegetable oil rich in linoleic acid reduces the risk of heart disease and death by lowering bad cholesterol blood levels.
As expected, the blood cholesterol levels in the group that consumed the vegetable oil dropped 13.8% from baseline, while that of the control group who ate saturated fats fell only 1% from baseline, according to the results published April 12 in The BMJ.
However, the reduction in blood cholesterol levels did not translate to reduced risk of death from cardiovascular incidence, as expected, the researchers found. Rather, they noted a higher risk of death associated with decreased serum cholesterol among participants 65 years or older, although not in people younger than 65 years.
Specifically, they found the risk of death among older participants increased 35% with every 30 mg/dL decrease in serum cholesterol.
In addition, they found 41% of participants in the vegetable oil group had at least one myocardial infarct, whereas only 22% of participants in the control group did. Likewise, participants in the intervention group did not have less coronary atherosclerosis or aortic atherosclerosis.
The researchers cautioned that “these findings should be interpreted with caution because of partial recovery of autopsy files.”
They added: “There was no association between serum cholesterol and myocardia infarcts, coronary atherosclerosis or aortic atherosclerosis in covariate adjusted models.”
To further test these findings, the research team analyzed all similar RCT and, again, failed to find any reduction in death from heart disease or other causes.
These findings support previous findings from the same researchers who in 2013 examined unpublished data from the Sydney Diet Heart Study and found the risk of death from heart disease and all causes was higher in those who replaced saturated fat with vegetable fat, despite a significant reduction in serum cholesterol.
“Thus,” the researchers write, “collective findings from randomized controlled trials do not provide support for the central diet-heart tenet that the serum cholesterol lowering effects of replacing saturated fat with linoleic acid translate to lower risk of coronary heart disease or death.”
Why lowering cholesterol levels did not reduce heart disease
The researchers hypothesize the disappointing disconnect between lower blood cholesterol levels and the risk of developing heart disease could be due to the use of vegetable linoleic acid as an agent of action.
They explain: “Consumption of vegetable oils rich in linoleic acid produces a wide range of biochemical consequences, including qualitative change in lipoprotein particle oxidation that could plausibly increase the risk of coronary heart disease.”
They add: “Hence, the clinical effects of replacing saturated fat with vegetable oils could reflect the net impact of decreasing low density lipoprotein while increasing its susceptibility to oxidation.”
They also note that consuming high levels of linoleic acid is not “natural,” with the average person consuming only about 6 grams per day from a diet of natural foods without added vegetable oil. However, today, many people in the US who eat packaged foods consume closer to 17 grams daily.
Given the researchers' findings, they suggest “the best approach might be one of humility, highlighting limitations of current knowledge and setting a high bar for advising intakes beyond what can be provided by natural diets.”
