Findings from the present investigation indicate that modifying dietary intake in accordance with a 21-day Daniel Fast 1) does not impact the hemodynamic or biochemical response to a high-fat meal, 2) lowers fasting BP, and 3) increases NOx. As it is currently unknown what specific impact these outcomes have on health, longer-term studies are needed to explore this line of inquiry.
Partaking in the Daniel Fast did not affect the hemodynamic response to the test meal. This may have been due to the fact that the test meal by itself had little effect on the hemodynamic variables measured in this study, thus leaving little room for improvement. However, fasting did lower pre-meal systolic and diastolic BP by 5 mm Hg and 8 mm Hg, respectively (Figure ), despite the fact that subjects' pre-fast BP was low and within normal range.
With reference to antioxidant capacity, we failed to note an increase in TEAC from pre to post fast, which opposes the results of our initial Daniel Fast study [12
]. In fact, average TEAC values in the present study were nearly identical at all times of measurement (Figure ). The lack of increase in TEAC may be explained in at least two ways: First, it is likely that the TEAC measure does not capture in a sensitive manner all changes in the antioxidant pool (e.g., phenol antioxidants, thiols, enzymes), as TEAC is simply a measure of "global" antioxidant capacity. Second, despite the potential increase in dietary antioxidant intake in the form of whole foods from pre to post fast (some of which may have contributed to TEAC and some of which may have not), the omission of coffee from subjects' diet during the fast may have resulted in a lower TEAC value (Increased whole-food antioxidants may have counteracted this decrease to allow for a maintenance
in TEAC.). This is because coffee has been reported to contribute to the majority of daily antioxidant intake [31
]. Although the Daniel Fast prohibits coffee consumption when partaken as a spiritual discipline, studies examining the Daniel Fast from a purely clinical perspective may consider allowing subjects who regularly consume coffee to continue doing so in an attempt to maintain their dietary antioxidant intake.
Along with the absence of change in TEAC from pre to post fast, we noted near identical concentrations for pre-meal TAG (Figure ). In our prior work with the Daniel Fast, we noted modest reductions in fasting TAG (11.5%), which we hypothesized might influence postprandial TAG concentrations, as such an effect has been reported previously [22
]. Neither the pre-meal or post meal TAG concentrations were different from pre to post fast. In much the same way as discussed for TEAC, it is apparent that pre-meal TAG concentrations do not completely influence the postprandial oxidative stress response to feeding. It is possible that other blood lipids such as cholesterol play a role in this response, as both total and LDL cholesterol concentrations decreased from pre to post fast (Table ). The fact that we did not measure the postprandial cholesterol response is a limitation of this work. Furthermore, a decrease in the production of ROS from pre to post fast likely plays a significant role in the resulting lowering in oxidative stress biomarkers. Direct assessment of ROS using electron spin resonance spectroscopy was not performed in the present design, which may be considered a limitation of this work.
In relation to ROS production, our noted decrease in total dietary energy, in addition to dietary protein (Table ), was thought to decrease ROS and the oxidative stress response to feeding, as both dietary energy [9
] and protein restriction [10
] is associated with decreased ROS. However, despite a decrease in kilocalorie intake of approximately 16% and protein intake of approximately 38%, we observed no statistically significant reduction in postprandial oxidative stress. While a greater reduction in these dietary parameters (or a longer time course of dietary intervention) may lead to more robust decreases in our chosen oxidative stress biomarkers, we must question the benefit of such further reduction. That is, participants consumed a relatively low kilocalorie diet and consumed an average of only 58.3 ± 4.9 g of protein daily during the Daniel Fast, which is slightly less than the current recommended amount of 0.8 g·kg-1
. Any further reductions may not be well-tolerated. Rather, maintaining this degree of reduction for a longer time period may be necessary and met with more favorable results.
Our failure to note findings of statistical significance may be partly due to our relatively small sample size. Moreover, although we included a variety of oxidative stress biomarkers in our design, additional measures may be considered in future experiments to better capture the redox status during the postprandial period. Of course, the physiological implications of any potential biochemical change need to be explored in future work with the inclusion of clinical measures (e.g., endothelial function, future cardiovascular disease risk). While elevated oxidative stress [32
] and impaired nitric oxide production [33
] appear to be correlated with disease progression, it is unknown what impact small changes in these variables might have on healthy individuals. This is emphasized when considering the relatively low values (both pre and post fast) that our subjects demonstrated for the measured variables (e.g., pre fast TAG values of 59 ± 7 mg dL-1
). Such low values in our sample of healthy, active subjects may have impaired our ability to note decreases of statistical significance from pre to post fast. The inclusion of subjects with hyperlipidemia may have allowed for greater potential for change in our measured variables from pre to post fast.
As expected, TAG, MDA, H2
, AOPP, and TEAC were each affected by the test meal consumption. Each of these values (except for TEAC) increased at 2 and 4 h post meal compared to pre meal, while TEAC decreased at these times. These findings replicate our prior work using high-fat meals to induce oxidative stress [20
]. In addition, NOx increased from pre to post fast, which may have implications with regards to vascular health and enhanced blood flow [33
While we failed to note any change of statistical significance in postprandial oxidative stress biomarkers from pre to post fast, subjects did appear to process the test meal more efficiently after the fast as compared to before the fast (as evidenced by an approximate 10% reduction in TAG and oxidative stress biomarkers). While this was our working hypothesis, we acknowledge the possibility that reducing the consumption of saturated fat and eliminating the consumption of processed foods for 21 days may have made subjects more
susceptible to the harmful effects of a high- fat meal. In much the same way as a "repeated bout effect" has been noted for exercise [35
], it is possible that such an effect may be present with routine high-fat feeding. That is, regular intake of high-fat meals may not present as significant of a metabolic stress due to the fact that the body is familiar with such a stressor and has adapted to handle this accordingly. Although this explanation was not the case in the present study, as subjects responded in a similar (or slightly more favorable) manner to the high-fat test meal despite abstaining from such foods for a 21-day period, such an effect may have negated some of the benefits of the Daniel Fast, resulting in our non-significant findings.
Although not a primary interest in the present design, we computed the correlations between each of our biochemical variables, including TAG. Table provides these data, which corroborate our prior work demonstrating both significant and strong correlations between blood TAG and a variety of oxidative stress biomarkers [20
]. As TAG is routinely measured in a clinical setting, while biomarkers of oxidative stress are not, it seems plausible that the simple measurement of serum TAG following administration of an oral fat tolerance test could serve as an estimation of postprandial oxidative stress. Future work using a larger data set inclusive of both TAG and oxidative stress biomarkers is needed in order to generate the requisite prediction equations. Furthermore, as the TAG response to feeding is strongly correlated to all measures of oxidative stress, it seems logical that attenuation in postprandial TAG should be the first line defense against an increase in postprandial oxidative stress. In fact, blunting the TAG response to high-fat feeding may be much more important than increasing antioxidant defense. In this way, the problem (ROS production) is controlled before
it presents itself and subsequently needs to be dealt with (via increased antioxidant defense). Interventions (both chronic and acute) aimed at minimizing the TAG response to feeding should be investigated (as has been done successfully with exercise [36
]), with a particular focus on understanding the molecular mechanisms relating elevated TAG and increased oxidative stress and disease.