Introduction
Christian Orthodox fasting (COF), is a vital subset of the Mediterranean diet (MD)
[
1,
2,
3,
4], which for religious reasons is considered to be deeply integrated in the cultural dietary behavior of a large part of the Greek population [
5,
6,
7,
8,
9] for prolonged periods (from 120 to 180 d) annually [
8].Orthodox monasteries follow this archetype pattern of diet throughout the year, with periods of more strict fasting rituals 2-6 weeks before religious celebrations, as a way of physical and mental prosperity and personal spiritual development [
1,
2]. However, besides the spiritual significance of COF, a plethora of cohort studies suggest that COF shares the beneficial effects of the typical MD by promoting specific cardioprotective mechanisms, including reduced intake of dietary cholesterol and fatty acids, thus providing optimal effects on plasma lipid concentrations [
9,
10]. These benefits have been mainly attributed to the integration of a plant-based diet along with characteristics of dietary restriction of animal products (meat, dairy products and eggs) [
6] and restriction of caloric intake during COF periods [
11,
12,
13,
14]. We have previously reported on the beneficial effects of COF on the adipokine profile [
7,
8,
14] as well as on glucose homeostasis in both monastic and general populations [
15], as markers for prevention of cardiovascular dyshomeostasis, with the exception of profound hypovitaminosis—D in Orthodox Monks, mainly due to their sartorial habits [
11,
16].
Additionally, restriction of food intake in specific time—frames during the day, has also been hypothesized to contribute to the benefits described above, a characteristic which attracted significant scientific and public interest during the last decade, through various intermittent—fasting patterns, practiced worldwide as a health-promoting diet [
17]. Time-restricted eating (TRE), includes specific time-frames of food intake during the day, which vary from 4-12 hours daily [e.g., 20 hours of fasting vs 4 hours of permitted food intake—20:4—as well as additional time frames (18:6,16:8 etc.)] [
18]. On the other hand, impairment of antioxidative capacity of vascular endothelium is an established aggravating factor for development of endothelial dysfunction and future cardiovascular major events [
19,
20]. On that basis, a considerable number of previous studies [
21,
22,
23,
24] have suggested that MD is strongly associated with favorable effects on oxidative status, implying a potential pathway for exerting its well—established cardiovascular benefits. However, results on COF as a vital subset of MD and its effects on oxidative status, particularly compared to other healthy nutritional patterns widely adopted by the general population, remain scarce.
Additionally, these potential interactions have so far not been investigated in conjunction with other metabolic conditions associated with endothelial dysfunction, including impairment of vitamin D status and insulin resistance, particularly in vitamin D deficient and overweight individuals. These results could elucidate potential mechanisms of MD—related effects on antioxidative capacity and also elaborate on the research hypothesis, which indicates the macro- and micronutrient synthesis and increased intake of food antioxidants, rather than the timing of food intake, as the cornerstone of attained metabolic benefits.
The present study attempted to evaluate the effects of COF in a group of vitamin D –deficient and overweight Orthodox nuns from Central and Northern Greece,comparedto the implementation ofTRE16:8 dietary regimen in a cohort of adult women from the general population from the same region, with regard to markers of endothelial oxidative status.
Results
Orthodox nuns were older than lay women (median age 42 vs. 38, p<0.001) but did not differ in median weight and BMI
(Table 1).Groups did not differ in body fat (%), lean body mass (%) and waist circumference,as well as degrees of physical activity, with the exception of intense activity, in which lay women reported higher rates. Regarding nutritional analysis,lay women consumed higher amounts of carbohydrates (gr) (194.3 ± 23.4 vs 159.6 ± 21.8),total and saturated fat (24.4± 0.6 vs 21.0 ± 0.1and 16.4 ± 0.0 and 12.7±0.0,respectively) whereas Orthodox nuns reported higher amounts of protein and fibre intake (36.1± 0.8 vs 24.2 ± 0.8).
Although expected, according to the study protocol, hypovitaminosis D evident in the Orthodox nuns’ group, resulted in significantly higher median serum PTH than among lay women (45.6 vs. 19.4, p<.001), after adjusting for seasonal variation. In addition,after adjusting for age and 25(OH)D3 concentrations in linear regression across all patients, PTH had a significant positive association with age (+6.0 pg/ml per 10-year increase in age, p<0.001) and a significant negative association with serum 25(OH) D3 status (–0.61 pg/ml per ng/ml increase in serum D3). Orthodox nuns demonstrated lower median fasting insulin concentrations (5.3 vs. 7.2, p 0.02) compared to lay women and evenafter adjusting for age and BMI, the difference remained significant; Of major interest is the fact, that insulin concentrations lacked a significant association with BMI or age in both groups. Regarding redox status, Orthodox nuns manifested a lower median GSH compared to controls (6.0 vs. 7.2, p .04) and a higher median TAC (0.92 vs. 0.77, p <.001). TBARS comparisons showed no significant difference between the two groups. After adjusting for age in linear regression, Orthodox nuns had a lower GSH concentration in serum (mean difference -1.7; 95% CI -2.7 to = –0.7, p .001) compared to controls, while the age effect was not significant (p=0.45). After adjusting for age, nuns had a higher TAC concentration in serum (mean difference 0.19; 95% CI0.13 to0.26, p <.001), whereas after adjusting for age,BMI and total fat in linear regression, nuns had a lower GSH concentration in serum (mean difference –1.6; 95% significant (p=0.45). After adjusting for age, nuns had a higher TAC concentration in serum (mean difference 0.19; 95% CI0.13 to0.26, p <.001), whereas after adjusting for age,BMI and total fat in linear regression, nuns had a lower GSH concentration in serum (mean difference –1.6; 95% CI –2.6 to = –0.7, p .001) compared to lay women, while the age and BMI effects were not significant. After adjusting for age and BMI, nuns had a higher TAC concentration in serum (mean difference 0.21; 95% CI0.15 to 0.27 p <.001); age, BMI and total fat, effects were not significant. No significant associations of oxidative status with 25(OH)D, PTH and markers of glucose homeostasis were evident.
Figure 1.
Concentrations of TAC in Orthodox Nuns and lay women group.
Figure 1.
Concentrations of TAC in Orthodox Nuns and lay women group.
Figure 2.
Concentrations of GSH in Orthodox Nuns and lay women group.
Figure 2.
Concentrations of GSH in Orthodox Nuns and lay women group.
Discussion
To our knowledge, this the first cross-sectional study reporting preliminary results on the comparative effects of COF on oxidative status in vitamin D deficient Greek Orthodox nuns and TRE (16:8) dietary regimen in a group of lay women with vitamin D sufficiency. These results indicated: i) increased antioxidative capacity (TAC) in the group of Orthodox Nuns after a 16 week period of COF compared to a 16:8 TRE, ii) increased GSH levels in the lay women group compared to the group of Orthodox nuns as well as comparable of TBARS levels in both groups, after adjusting for several confounders, which suggest potential diverse effects of COF and TRE on oxidative status.
MD is a plant-based diet, rich in fruit, vegetables, nuts, herbs, with fewer fish and dairy products and with less red meat and red wine. MD includes various nutritional compounds, with well-established beneficial effects on oxidative status. A plethora of previous basic and clinical studies suggested that MD has been shown to be one of the healthiest eating patterns, with various metabolic benefits, partly mediated through its antioxidant capacity [
34,
35]. Dai et al. studied the ratio of reduced to oxidized glutathione (GSH / GSSG) in twins. The higher the ratio, the lower the oxidative stress, giving a result of a higher ratio up to 7% in individuals who followed the Mediterranean diet, regardless of the adjustment of the energy intake [
36]. In a sub-cohort of The PREDIMED trial, participants with
high cardiovascular risk were randomized to a Mediterranean diet supplemented with extra-virgin olive oil and manifested a significant reduction in cellular lipid levels and lipid oxidation, as well as malondialdehyde concentrations in mononuclear cells, without changes in serum glutathione peroxidase activity [
37]
.
Documented benefits of MD include consumption ofunsaturated fatty acids, found in olive oil, which contain 3,3dimethyl-1-butanol, thuspreventing the formation of trimethylamine-1-oxide, one of the oxidants related to cardiovascular events [
38,
39].
Additionally, MD synthesis is rich in oleic-acid and alpha-linoleic-acid,found in nuts, fruit and vegetable flavonoids, as well as omega-3-polyunsaturated-fatty-acids, and fiber and polyphenols, all of which have anti-oxidative, anti-bacterial and anti-inflammatory effects [
40,
41,
42].
Moreover, whole-grains, as a vital compound of MD, contain a polyaminecalled spermidine, which has been shown to extend chronological life-span in flies, nematodes, rodents, and human cells. Spermidine is known to inhibit histone acetyltransferases, which results in higher resistance to oxidative stress [
43]
.
TRE has been also the objective of recent studies regarding its potential beneficial effects on cardiometabolic health. Given the fact that hormones undergo a circadian rhythm, metabolic and stress hormones as insulin, cortisol, growth hormone and melatonin undergo the same variation, giving different levels between a calorie-restricting diet and intermittent-fasting diet, which restricts the feeding time in certain hours [
44]. Mc Allister et al. studied the impact of intermittent fasting on markers of cardiometabolic health, measuring several markers of inflammation, OS, and cardiometabolic health (insulin, ghrelin, leptin, glucagon, adiponectin, resistin, advanced glycated-end products (AGE), advanced oxidation protein products, total nitrite-nitrate levels, tumor necrosis factor-α, interleukin (IL)-6, IL-8, IL-10and showed that time-restricted feeding resulted in significant reductions in advanced oxidation protein products (∼31%) and AGEs (∼25%); however, no other changes were found [
45]. Recent randomized clinical trials also demonstrated that a
6-hr feeding period for 5 weeks improved insulin sensitivity, β-cell responsiveness and oxidative stress, irrespective of weight loss [
46]
. These results were also previously confirmed by other groups,where
4- and 6-h TRE for 5 weeks, resulted in a reduction of 8-isoprostane, as a marker of oxidative stress to lipids,4-hydroxynonenal adducts, protein carbonyls and nitrotyrosine [
47]
.
COF is a plant-based subset of the traditional MD followed for more than a thousand years from a large part of the Greek Orthodox general population for religious purposes from 90–150 days per year. Greek Orthodox monasteries adhere to this dietary regimen throughout the year, with the addition of TRE (usually 16:8) characteristics in their daily dietary regimen, which is strictly followed by all members of the monasterial community, comprising an optimal sample for nutritional studies .We have repeatedly reported on the effects on COF on body weight, lipid parameters, adipokines and vitamin D status, regarding the existence of severe hypovitaminosis D in Orthodox male monks, mainly due to their sartorial habits.
However, this is the first report on the effects of COF on oxidative equilibrium, particularly compared to a health –promoting pattern like TRE.
Our research hypothesis raised the question for non-inferiority of TRE compared to COF, in a vitamin D deficient monastic population (as most similar monastic communities in Greece), taking into account that women included in the TRE, were not instructed to follow a MD—specific dietary pattern. According to previous results, chronic vitamin D deficiency is a state of increased oxidative stress, which reduces the capacity of mitochondrial respiration, through modulating nuclear mRNA down regulating the expression of complex I of the electron transport chain, reducing of adenosine triphosphate (ATP),resulting in increased formation of ROS, augmenting oxidative stress [
48].
Maintaining optimum levels of redox biomarkers is crucial for preventing oxidative damage, supporting detoxification processes, and ensuring proper immune function. Previous literature proposed that clustering of high and low GSH levels might provide strong causality for type 2 diabetes and metabolic syndrome [
48]. Our results failed to suggest a superiority of COF over TRE, in a group with confirmed MD-type dietary regimen and TRE characteristics as Orthodox nuns, compared to a 16:8 without specific MD—related dietary characteristics.
A plausible explanation could be that the general population following a TRE pattern comply with a healthy dietary pattern, which despite not being identical to MD,also exerts benefits on GSH concentrations, always taking into account the limitations of this study. Another explanation, could lie on the potential adverse effects of hypovitaminosis D, evident in Orthodox nuns included in this study, on GSH concentrations, as previously reported [
12]. Vitamin D supplementation in this group of vitamin D deficient nuns could elucidate this potential biological association on GSH status. TRE could also have independent beneficial effects on oxidative status, which are evident without strict adherence to a MD-related pattern, as previously reported [
12]. Finally, our study failed to establish an association of impaired vitamin D status and oxidative markers, which could be attributed to its cross-sectional design. This study has several limitations and can only be considered as a pilot study, with findings which definitely require confirmation in a prospective study.
In detail, the number of included participants was relatively small; however, this is a representative sample of Orthodox nuns, according to their dietary and physical activity plan. We have also not included a detailed analysis regarding the intake of the dietary antioxidatives in the two groups, which could explain diversity in markers of oxidative status. Finally, since no baseline evaluation, prior to the implementation of dietary interventions, was feasible for both groups, we were unable to establish causal associations.
In conclusion, results of this small pilot study indicate that both dietary regimens have advantages over oxidative markers, compared to each other, with increased TAC in the groups of Orthodox Nuns after a 16th-week period of COF in comparison to increased GSH concentrations in the lay women group following 16:8 TRE, and comparable concentrations of TBARS. Future randomized trials are required to investigate superiority or non-inferiority between these dietary patterns, in the daily clinical setting.