In this cross-sectional study on the adult population of RaNCD cohort, we detected a positive effect of Kermanshah ghee on AIP index. There are enough studies about the influence of edible lipids on lipid profile fraction but data are rare about edible lipids and AIP. None of the discused studies reported AIP, but we calculate it based on their HDL-C and TG data. According to this article, milk-based lipids such as Kermanshah oil and butter acts better than vegetable one’s.
Despite high SFAs and cholesterol content, we observed consumption of Kermanshah oil has reduced the amount of AIP in male and female, Therefore, its impacts on AIP is favorable and has a protective role in the incidence of CVDs. In accordance with our findings, the results of a study by Rawashdeh et al in Jordan showed that a diet based exclusively on ghee resulted in a decrease in TG, an increase in TC, an increase in TC / HDL-C ratio and an increase in LDL-C / HDL-C but a diet based exclusively on olive oil results in an increase in TG, a decrease in TC, a decrease in TC / HDL-C ratio, and a decrease in LDL-C / HDL-C ratio. This is calculable that AIP has increased during the intervention in the olive oil group compared to starting point slightly, whereas ghee consumption decreased AIP in Jordanians.
The results of a cross-sectional study during 2009–2011 period by Vyas et al has reported an inverse relationship between the amount of ghee and the history of CHD in the urban North Indian adults; they have concluded that people with the highest consumption of ghee per month and the lowest consumption of vegetable oil (mustard) have a better history of CHD.
Also the result of another clinical trial study in India by Shankar et al has shown that both mustard oil and ghee (10% of energy intake) have decreasing effects on AIP decreased for eight weeks .
Similar to our findings, the results of a randomized clinical trial on 206 Iranian adults are implied that ghee consumption has decreased the amount of AIP slightly .
We observed that butter consumption had reduced the amount of AIP in two genders, and the relationship between butter and AIP was favorable similar to Kermanshahi oil consumption.
In agreement with us, Asadi et al. concluded that yogurt butter has a positive effect by increasing HDL-C in the animal model.
A meta-analysis study that analyzed 9 studies in 15 countries concluded that butter has a neutral or weak effect association with overall mortality, cardiovascular disease, and diabetes.
The Nurses' Health Cohort Study findings reported that dairy fat consumption is associated with an increased risk of IHD.
The result of a prospective cohort study in the United States on 2907 people over the age of 65 has shown that there was no significant relationship between pentadecanoic, heptadecanoic, and trans- palmitoleic phospholipids (as biomarkers of dairy fat intake) with total mortality and incidence of CVDs.
In another meta-analysis study of 13 studies, it was observable that a higher intake of dairy fat was not associated with an increased risk of cardiovascular disease.
We observed that in both males and females with increasing margarine intake, AIP did not change, and its effect was almost neutral. In contrast with our finding, the results of a randomized clinical trial on 206 Iranian adults are shown that margarine consumption has decreased the amount of AIP slightly. According to Iranian standards, 5 types of margarine are produced with different amounts of Trans fatty acids; perhaps the difference of results is related to the type of consumed margarine in the two studies.
Hydrogenated or partial hydrogenated oil
In the present study, both males and females had a negative and slightly inverse relationship between hydrogenated vegetable oil and AIP, although no significant relationship was found after controlling for confounding variables. In general, the hydrogenated vegetable oil not only did not increase AIP but also slightly reduced it. This finding is somewhat different from previous studies because most of them implied the adverse effect of hydrogenated vegetable oil on the lipid profile[15, 30]. Nour et al. in Egypt have done a study that represented based on HDL-C and TG data, AIP was the lowest in the ghee group and the highest in the hydrogenated vegetable oil group.
The results of Nour et al study in Egypt on hydrogenated vegetable oil are somewhat different from the results of our study that is due to the fact that Egyptian hydrogenated vegetable oil is made from palm oil while Iranian hydrogenated vegetable oil is made from a mixture of soybean oil, canola, corn, etc[6, 12, 15]. As we know, palm oil is the source of atherogenic fatty acids naturally.
In contrast with our findings, the aforementioned randomized clinical trial results on 206 Iranian adults were shown that hydrogenated vegetable oil consumption had increased the amount of AIP slightly. This difference may be reasonable because their study carried out at 2009 while we collected data in 2013; the Trans fatty acids reduction program was implemented in Iran in 2013 so that the amount of trans fatty acids in hydrogenated vegetable oils should be less than 2 percent. Asgary et al. reported that the amount of trans fatty acids in hydrogenated vegetable oils was about 30% at 2009[12, 13].
There have been many studies on the adverse effects of vanaspati, which is a type of hydrogenated vegetable oil in India, but it should be remarkable that vanaspati is made up of 20 different oils and the amount of trans fatty acid is also high; therefore, the vanaspati available in India differs from Iranian hydrogenated vegetable oil[5, 32]. Although various studies have reported adverse effects on hydrogenated vegetable oil[33, 34], the effect of hydrogenated vegetable oils depends on the amount of trans fatty acids and is not a risk factor if trans fatty acids be controlled [33, 35].
Un-hydrogenated (liquid) oil
Unexpectedly, the relationship between liquid oil consumption and AIP in both genders was direct and it can be said that liquid oil consumption had an atherogenic effect; however, after controlling for confounding variables, it was significant. In a clinical trial study conducted in Iran during 2009, liquid oil consumption had no effect on AIP, but in the current study, its effect was unfavorable, and it is maybe that increasing the amount of liquid oil consumption lead to increasing the chance of CVDs. In our opinion, the first reason of this contradiction is related to type of study so that their study was a clinical trial and they used a specific liquid oil, whereas in our study only liquidity was considered as un-hydrogenation. Maybe the second reason is improper usage of these oils in our study. Both Frying oils and cooking oils are liquid but their properties are different. If cooking oil is used instead of frying oil, its fatty acids will be oxidized and peroxided, which have harmful effects on serum lipid profile.
We conclude that Kermanshahi oil and butter have decreasing effects on AIP, the effect of margarine was neutral, hydrogenated vegetable oil has trace decreasing effect whereas un-hydrogenated vegetable oil has increasing effect on it.
Summarily, we can say that Kermanshahi oil and butter have covered the effect of un-hydrogenated (liquid) oil so that total oil consumption in men had no effect on AIP but in women slightly reduced AIP. We observed that although Kermanshahi oil and butter are rich in cholesterol and saturated fatty acids but have a favorable effect on AIP. Maybe that’s why Ayurveda medicine has considered ghee (clarified butter) to be the healthiest source of edible fat for thousands of years.
Study strengths and weaknesses
This study will be one of the first studies in Iran to investigate the relationship between different types of edible oils and AIP because other studies have been done based on lipid profile fractions. Overall, this study has several strengths, most notably the high sample size, the study of all types of oils (especially kermanshahi oil), and trained nutritionists' data. The FFQ questionnaire was confirmed and validated formerly. Also this study had some weaknesses such as the amount of oils per day is so low that therefore the effect of the amount of oils per day on AIP is neglectable, quality of oils in the same group of oil are different. Furthermore, given the questionnaire-based nature of the current study, the finding may have been affected by information bias. Moreover, resembling other cross-sectional studies, it is hard to declaration a cause-and-effect relationship.