The changes in blood levels of fatty acids and carotenoids indicated that subjects were making the appropriate dietary changes, but changes in blood levels were of smaller magnitude than the changes in dietary intakes. In the Mediterranean arm, the increase in total MUFA was about 25% while SFA and PUFA each decreased by about 5%. These changes in plasma fatty acids reflected, but were smaller than the large changes in dietary intakes of fats, which included a 48% increase in dietary MUFA from 7-day food records [23
]. The increases in dietary and plasma MUFA were larger than that obtained in the Lyon Heart Study, which had several positive health endpoints and utilized counseling for a Mediterranean diet together with providing a canola-oil based margarine [44
Similar to the changes in plasma fatty acids, the changes in plasma carotenoids in the Mediterranean arm reflected the increase in fruits and vegetables, but were smaller. While reported fruit and vegetable intake doubled [23
], total carotenoids only increased by 55%. This increase in total carotenoids is similar to that in our previous 9-a-day high fruit-vegetable intervention of women at increased risk for breast cancer and that achieved in a large intervention study of breast cancer survivors [45
]. This indicates that blood carotenoids likely changed as much as could be expected with the Mediterranean intervention that requires consumption of 7–9 fruits and vegetables/day. The changes in the control arm were generally smaller and not statistically significant.
Most of the changes in blood fatty acids and carotenoids with the Mediterranean diet were larger at 6 than at 3 months, indicating that it took some time to comply with the requested dietary changes. In our previous study with a 9-a-day fruit and vegetable intervention, the increases were significant at 3 months and reached a plateau after that [45
]. This could be due to the less complex nature of the intervention when focusing only on fruits and vegetables versus the more complex changes required with a Mediterranean diet.
The Mediterranean diet did appear to result in a decrease in blood levels of γ-tocopherol. This was not significant over 6 months of study, but is of interest and likely results from decreased intakes of vegetable oils rich in vitamin E as subjects started using more olive oil. Vitamin E intakes were not addressed with the exchange list diet. This may be an area for concern; however, vitamin E needs may be lower when PUFA intake decreases [47
]. A low-fat diet can also decrease γ-tocopherol levels [45
Despite the seemingly good compliance to the Mediterranean diet, changes in blood measures indicative of diabetes and cardiovascular risks were not evident. A review of other Mediterranean interventions has indicated that many did find favorable effects on LDL, but most of these studies were conducted in persons with increased cardiovascular risks or metabolic syndrome [26
]. In a Canadian study of healthy women, LDL did not decrease overall but it did decrease in person in the highest tertile of LDL at baseline [48
]. Favorable effects on insulin resistance were also seen in many but not all studies, and in two large studies with favorable effects on insulin, there was a weight loss associated with the Mediterranean intervention [26
]. Changes in blood lipids with Mediterranean diets likely would be evident if there was a concomitant weight loss [49
]. In this study, however, weight maintenance was a goal to isolate the effects of diet quality, as much as possible.
Important limitations of the present study are that the women who volunteered for the study were highly educated, the study was small and it only lasted 6 months. In addition, the exchange list diet targeted only fat, fruit and vegetable intakes. The exchange list could be further modified to include omega-3 fats and whole grains, both of which appear important for cancer prevention.
In summary, the changes in blood levels of fatty acids and carotenoids in the Mediterranean diet arm were consistent with the previously reported dietary changes [23
]. In particular, plasma levels of MUFA increased by about 25% and total carotenoids increased by 55%. The increases in plasma carotenoids were likely related to increases in fruits and vegetables, except for increases in lycopene which clustered with an increase in saturated fat. This may help explain the poor correlations observed previously for dietary and serum lycopene [50
]. The increases in plasma MUFA were associated with decreases in plasma PUFA, likely representing a shift in the type of oils consumed. Despite these changes in diet, there were no measurable effects on plasma lipids, glucose, insulin and C-reactive protein in this study population of young, healthy women. Effects of the Mediterranean intervention on other measures of health and biomarkers of cancer risk, however, have yet to be explored.