Written by Joyce Smith, BS. Re-evaluation of previous studies validates that increasing dietary saturated fats reduces the risk for coronary heart disease in spite of increasing serum cholesterol.
Two studies, the Sidney Diet Heart Study (SDHS) (1966-77) and the Minnesota Coronary Experiment (MCE) (1968-7310), have shown that replacing dietary saturated fats with dietary omega-6 linoleic acid lowers both serum total cholesterol and low density lipoprotein cholesterol. These findings contribute to the existing diet-heart-hypothesis that lowering serum cholesterol reduces or prevents coronary heart disease and death. 1,2
This causal relationship, which has never been demonstrated in a randomized controlled trial, remained questionable until Ramsden, in 2013, 1 recovered previously unpublished mortality data for coronary heart disease and cardiovascular disease from the SDHS Study (1966-77). Incorporating this missing data into his systematic review and meta-analysis showed him that replacing saturated fat with vegetable oil rich in linoleic acid, while lowering serum cholesterol, significantly increased the risk of death from coronary heart disease and all causes. Specifically, compared to the control group, the intervention group had an increased risk of all-cause mortality (P=0.051) cardiovascular mortality (P=0.037) and mortality from coronary heart disease (P=0.036). 1
Recovering another set of unpublished documents and data from the Minnesota Coronary Experiment (MCE) (1968-73) gave Ramsden and co-researchers 2 a further opportunity to evaluate the hypothesis that lowering serum cholesterol levels reduces the risk of heart disease. In a randomized controlled clinical trial, and using recovered unpublished documents and raw data from the MCE (1968-73), he once again conducted a previously impossible comprehensive analysis to determine the effects of linoleic acid on death from coronary heart disease and cardiovascular disease. His analyses included data on a randomized cohort of 9,423 women and men aged 20-97, serum cholesterol data on 2,355 participants who had been on the high linoleic acid diet for a year or more, and data from 149 completed autopsy files.
Results of this 2016 study paradoxically showed that those study participants with greater reductions in serum cholesterol had a higher rather than a lower risk of death.
- Participants on the high linoleic acid diet had significantly lower serum cholesterol compared to the control group (P<0.001) and baseline (P<0.001). Higher adherence to the linoleic diet (fewer skipped meals) was also associated with a more pronounced reduction in serum cholesterol (P<0.001)
- The control diet (which did not alter saturated fat) increased dietary linoleic acid by 38% and modestly but significantly reduced serum cholesterol compared to baseline (P< 0.001). Higher adherence to the control diet was also associated with a greater reduction in serum cholesterol (P=0.004)
- A strong association was found between decreasing serum cholesterol and increased risk of death between the intervention and control groups (P> 0.16) This association was strong in the subgroup aged 65 and older where a 30mg/ld. decrease in serum cholesterol was associated with a 35% higher risk of death; however, for those under age 65, at baseline there was no association between serum cholesterol levels and risk of death.
Partial recovery of autopsy files (149 files) of MCE ((1968-7310) showed that 41% (31/76) of participants in the intervention group had at least one myocardial infarct, compared to only 22% (16/73) of the control group participants.(P =0.035). (This partial recovery should be interpreted with caution since only 149/ 295 of autopsy files were recovered.)
A final systematic review and meta–analyses was done on randomized controlled trials in which dietary saturated fat was replaced with linoleic acid–rich vegetable oils. Only five trials were found. Of the 10,808 participants, 324 deaths were due to coronary heart disease and 1001 from all causes. A meta-analyses of these five trials revealed that replacing saturated fat with linoleic acid–rich vegetable oils did not reduce death from cardiovascular disease or all-cause mortality.
Researchers concluded that while replacing saturated fat with linoleic acid effectively lowered serum cholesterol, it did not translate to a lower risk of death from coronary heart disease or all causes. They added, “MCE findings add to a growing evidence that incomplete publication has contributed to overestimation of benefits, and underestimation of potential risks, of replacing saturated fat with vegetable oils rich in linoleic acid.”
Sources: Ramsden CE, Zamora D, Leelarthaepin B, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ 2013;346:e8707. doi:10.1136/bmj.e8707.
© Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, http://creativecommons.org/licenses/by-nc/3.0/.
Click here to read the full text study.
Ramsden, Christopher E., Daisy Zamora, Sharon Majchrzak-Hong, Keturah R. Faurot, Steven K. Broste, Robert P. Frantz, John M. Davis, Amit Ringel, Chirayath M. Suchindran, and Joseph R. Hibbeln. “Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73).” bmj 353 (2016): i1246.
© Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, http://creativecommons.org/licenses/by-nc/3.0/.
Click here to read the full text study.
Posted July 18, 2017.
References:
- Ramsden CE, Zamora D, Leelarthaepin B, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. Bmj. 2013;346:e8707.
- Ramsden CE, Zamora D, Majchrzak-Hong S, et al. Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73). bmj. 2016;353:i1246.
