Given its huge role in the U.S. and global food supply, the amount of human research on the health effects of soybean oil that has been conducted is limited. So, any clinical trial involving soybean oil substantially contributes to the literature. This is certainly the case for a new 3-month study from China that compared the effects of soybean oil with olive oil and camellia oil.1 Camellia oil has a similar composition as olive oil as it contains about 79% oleic acid. The major finding of this study is that with respect to the primary endpoint – change in body weight — there were differences among the three oils. The authors concluded that olive oil and camellia oil had a more favorable effect on cardiometabolic profiles than soybean oil; however, a closer look at the data suggests this is the not case.
This study enrolled 90 Chinese women aged 35-69 at risk of cardiovascular disease (CVD) who were randomly divided into one of three groups. Of these 90 women, 83 (92%) completed the trial. During weekdays, the women were provided lunch and dinner containing 30g/d of the test oils. The participants were instructed to avoid consuming added oils at their breakfast meal and at all weekend meals. Given that the diets were designed to provide about 2,200 kcal/d (2,100-2,300) and were 25% (20-30%) fat on a caloric basis, the oil represented about 12% of total calories and about half of total fat consumed.
As noted previously, the primary outcome was change in body weight, but the study also included 25 other outcomes such as lipids, blood pressure, inflammation, muscle contraction, heart failure, homocysteine, and liver enzymes. Of these 25 measurements, only 2 differed among the 3 oils. It is notable that there was no difference in markers of inflammation which included hypersensitive C-reactive protein and interleukin-6 and interleukin-8. Thus, this study shows high omega-6 polyunsaturated fat intake does not increase inflammation, which is consistent with the literature, but is a point often argued otherwise.2
The conclusion about the favorable effect on cardiometabolic profiles of the 2 high oleic acid oils versus soybean oil was based on 2 outcomes: HDL-cholesterol (HDL-C) and aspartate aminotransferase (AST). Bear in mind, however, that when examining 25 endpoints, there is a decent likelihood that some difference will emerge by chance. Furthermore, even the differences in the 2 outcomes that achieve statistical significance warrant a cautious interpretation.
At trial termination, HDL-C (mmol/l) decreased by 0.11 and 0.10 in the soybean oil and camellia oil groups, respectively, but increased in the olive oil group by 0.02. The difference between soybean oil and olive oil was statistically significant (p=0.03). By the way, the difference between camellia oil and olive oil was almost the same as between soybean oil and olive oil (0.13 mmol/l). However, LDL-concentration (mmol/l) increased by nearly twice as much in response to olive oil as it did in response to soybean oil (0.25 vs 0.44). Consequently, there was little difference in the LDL-C to HDL-C ratio. When considering there were also no differences in apo-B, apo-A, Lp(a), triglycerides, and systolic and diastolic blood pressure among the 3 oils, the data overall indicate the effect on CVD risk also did not differ.
AST is an enzyme that is found mostly in the liver, but it’s also in muscles and other organs. When cells that contain AST are damaged, they release the AST into the circulation. AST is a possible indicator of CVD risk.3 The change in levels (U/L) of AST between soybean (1.79) and camellia oil (-1.72) did differ (p=0.02) but as noted previously, the final values (U/L) for the soybean oil (20.49) and camellia oil (21.08) groups were almost identical because the soybean oil groups started out lower.
In conclusion, there were no differences among the 3 oils on the primary endpoint and no differences in the vast majority of secondary outcomes measured. Perhaps the most notable finding is that inflammation was not increased in response to soybean oil, despite its high omega-6 polyunsaturated fat content. This finding is consistent with the extensive literature on this topic.
References
- Wu M-Y, Du M-H, Wen H, Wang W-Q, Tang J, Shen L-R. Effects of n-6 PUFA-rich soybean oil, MUFA-rich olive oil and camellia seed oil on weight and cardiometabolic profiles among Chinese women: a 3-month double-blind randomized controlled feeding trial. Food & function 2022.
- Messina M, Shearer G, Petersen K. Soybean oil lowers circulating cholesterol levels and coronary heart disease risk, and has no effect on markers of inflammation and oxidation. Nutrition 2021;89:111343.
- Ndrepepa G, Holdenrieder S, Cassese S, Xhepa E, Fusaro M, Laugwitz KL, Schunkert H, Kastrati A. Aspartate aminotransferase and mortality in patients with ischemic heart disease. Nutrition, metabolism, and cardiovascular diseases : NMCD 2020;30:2335-42.
This blog is sponsored by SNI Global and U.S. Soy.
