The most important finding of this study is that most serum lipid variables decreased significantly over the fasting periods. Fasters, as compared to controls, had decreased levels of mean end- total cholesterol, LDL-C, LDL/HDL-C ratio and BMI. Several genetic factors account for the variation in cholesterol levels and obesity indices, however, we believe that the possibilities of genetic differences between the two groups are minimal since the population of Crete is stable with a long history over 4000 years. In addition to this, the ApoE genotype distribution found no differences between the two groups (fasters vs controls). In the fasters' group the mean decrease within all three fasting periods was 9% for total cholesterol and 12% for LDL-C. However, it was observed that during non-fasting periods when fasters returned to their usual dietary habits, total cholesterol and LDL-C increased by 6% and 9% respectively. This shows that the reduced end-total and LDL cholesterol concentrations that were observed within the fasting periods were not sustained when the subjects returned to their usual dietary habits even though the increase did not reach the initial pre- levels. The reduction in HDL that occurred in fasters is a common finding with low-fat and vegetarian diets [28–31]. The findings above are in agreement with the results reported by Barnard et al who conducted a strict vegetarian-diet intervention study for 5 weeks on 35 women [30]. The intervention diet consisted of grains, legumes, vegetables and fruit. After the intervention diet phase total cholesterol, LDL and HDL were decreased by 13.2%, 16.9% and 16.5% respectively [30]. BMI was also significantly reduced (p < 0.001) while, in agreement with our findings, the TC/HDL and LDL/HDL ratios remained unchanged (table 5)[30]. Similar were the findings in another 6-week vegetarian-diet intervention study by Masarei et al [28] and in a 12-week low-fat-vegan-diet intervention study by Nicholson et al [32]. Lee [33] and Hoffman [34], who compared omnivores with lacto-ovo-vegetarians, found no difference in LDL/HDL ratio between the two groups. The contrasting results on LDL/HDL ratio could be attributed to differences in the population samples studied.

Nieman et al [14] and Toohey et al [35] investigated Seventh-Day Adventists with similar demographic and life-style factors and with comparable diets and dietary habits to our cohort. They found that lacto-ovo-vegetarians and lifetime strict vegetarians had lower concentrations of total and LDL cholesterol when compared with non-vegetarians and lacto-ovo-vegetarians respectively (p < 0.05) [14]. Toohey et al found also found lower levels of BMI, triacylglycerols and TC/HDL ratio [35]. The present study showed that women had lower levels of LDL/HDL ratio and TC/HDL ratio, which is also a better predictor for CHD in women [36–38]. This is explained by the higher concentrations of HDL that women have compared to men [39].

The positive association of waist-to-hip ratio with total and LDL cholesterol is in agreement with other studies that correlate waist-to-hip ratio with coronary risk factors and CHD prevalence [40–42]. Waist-to-hip ratio measurement is a simple and cost-effective measure that contributes in predicting abnormal lipoprotein levels and increased risk of cardiovascular disease.

Both the fasting and control groups had mean BMI in the overweight category. Fasting had a small but statistically significant impact on fasters' BMI at the end of the fasting periods that was not sustained in non-fasting periods. In accordance to the results in this study, Haddad et al studying a group of vegans and nonvegetarians found significantly lower BMI levels in the vegan group [43]. Moreover, others found that vegetarians have lower BMI than meat eaters [44–46]. At the same time following a Mediterranean-style diet has also been proven to be beneficial to weight loss [47]. As regards religious fasting some studies associate it with weight loss and decline in BMI [2, 3] while others do not [4, 5, 48].

Educational level was not found to influence any of the blood lipid variables in this study (Table 3). This was an unexpected result since higher education is associated with better health care and awareness whereas low educational level has been related to unfavorable lipid profile [49], all-cause and CAD mortality [50] and hypertension [51].

The beneficial changes seen in fasters diet during the fasting periods, especially regarding energy intake, total fat and fiber consumption, can also explain the reductions in the biochemical and obesity indices. A recent study of the University of Crete showed that the Christian Orthodox nuns' diet was very low in cholesterol and in saturated fat intake (6% of total energy intake), and high in fiber and antioxidant vitamins [16]. This could be attributed to nuns' high consumption of fruit, vegetables, cereals and legumes. In another study Haddad et al found that vegans consume more grains, vegetables, fruit, legumes and seeds and as a result their diet consists of more dietary fiber and less dietary cholesterol [43]. It is well known that reduced intakes of dietary SFA and cholesterol lower total and LDL cholesterol concentration and are associated with low risk of cardiovascular diseases [52, 53]. The Orthodox Christians' diet, which is based on vegetables, legumes, fruit, cereals, bread and olive oil, is a Mediterranean-type of diet with periodic abstinence from meat and other animal products during the fasting periods. Numerous investigators [54–56] have recognized the beneficial role of the Mediterranean diet in cardiovascular diseases, and the protective effect in terms of cancer and longevity have also been noted [57, 58]. In addition, supplementary studies have associated religiosity with good health [10]. This has been confirmed in a recent study by Chliaoutakis et al [59], which is the only published work to date which investigates the association between the Orthodox Christian lifestyle and health. Chliaoutakis et al found that devout Orthodox Christians adopt healthier life-styles and that religion has a substantial impact on mental and physical health-related behaviors [59]. In the present study, contrary to Chliaoutakis' findings, the physical activity of the two groups (fasters vs controls) did not differ in any of the testing periods.

Our study attempts to provide an understanding of the impact of Christian Orthodox fasting on serum blood lipids and obesity indices before and at the end of the three major fasting periods. Compared to controls, fasters presented decreased lipoproteins and BMI levels. These results support our hypothesis by highlighting the beneficial influence of Christian Orthodox fasting on lipoprotein profile and prevalence of obesity.