During the ninth month of the lunar calendar, healthy adults Muslims are not allowed to drink and eat from dawn (El fajr) to sunset (El moghreb) during 29 or 30 days (i.e., based in the Moons observation) (1-3). Thus, food and fluid intake are allowed only during the hours of darkness (4, 5). Advancing by eleven days every year, Ramadan intermittent fasting (RIF) could occur in any seasons (6). When RIF occur during the summer months, the fasting period could exceed 15 hours in some countries and this could adversely affect physical performance (7, 8).
It has been reported that RIF affect meal frequency (9) and quantity (10) and fluid intake (11-16). Not only is the daily eating pattern, but also the food type consumed during RIF is always different from that usually eaten at pre- and post-RIF (17). In this context, increases in preference for fatty food (11, 15, 18, 19) and decreases of water intake (11, 13) has been shown during RIF. These changes can influence substrates utilization and storage and could modify body composition (11-14, 20-22). Likewise, changes in some hematological and biochemical parameters indicative of hydration status and renal function were reported (11, 13-15, 20, 21, 23-25). During RIF, adults Muslims often maintain their physical activity levels for recreation and health purposes (26-28). In the same way, many athletes continue to train or participate to competitions during RIF (29-31). During the last years, RIF occur during the summer and thus exercise training places additional stresses on performances (32-34) and energy metabolism and fluid/electrolyte balance (13, 35). The purpose of this review article is to describe the results of published scientific research which has examined the effect of RIF on indicators of health (i.e., hematological and biochemical parameters) in physically active persons.
The literature concerning the biochemical and hematological changes during RIF was reviewed using PubMed/MEDLINE and Google Scholar database, and cross referencing the selected manuscripts with the following keywords: Ramadan fasting, Ramadan observance, hematological, biochemical, renal function, hydration status, lipid profile, physical activity, physically active and sport. The last search was completed in August 28, 2018
2. Hematological Parameters
Blood hemoglobin concentration and hematocrit are two hematological parameters utilized in body water status evaluation of athletes (36). The few studies that have investigated the effects of RIF on these two markers of hydration status in physical activity practitioners have reported conflicting results. In fact, both hemoglobin and hematocrit have been increased in physically active men (13), rugby union players (11) and rugby sevens players (14) indicating a dehydration state. Dehydration during RIF has been attributed to reductions in water intake (11, 13, 14). Decreases in hemoglobin and hematocrit were reported in footballers (37) possibly because the collection of blood samples was realized in the morning. Recently, Aloui et al. (28) showed that hemoglobin and hematocrit values of amateur footballers were superior during compared to before RIF and were higher at 05:00 P.M. compared to 07:00 A.M. during RIF. Accordingly, these data indicate that the subjects were marginally more hypo-hydrated in the afternoon than in the morning during RIF (3). Tayebi and associates (38) evaluated the effect of a hypertrophic training program (i.e., three sessions/week) during RIF on hematological parameters in weightlifters. The authors reported that hemoglobin, hematocrit, mean corpuscular hemoglobin, red blood cell count, distribution index of red blood cells and mean corpuscular volume did not change between before and during RIF (38). Likewise, it has been also demonstrated that blood platelets did not change during RIF (13, 38, 39). However, during RIF, micronutrient deficiencies (i.e., iron and vitamins) might decrease blood platelets in physically active men (40).
3. Biochemical Parameters
3.1. Plasma and Serum Electrolytes
As a hydration status indicator (36, 41), serum sodium has been observed to increase during RIF in sedentary men; but interestingly no-changes were reported in physically active subjects (40). Likewise, Maughan et al. (37) showed that serum sodium concentration did not change during RIF in footballers. It may be that physically active individuals, particularly athletes, concentrate on ensuring adequate fluid intake in the evening hours. However, during hot and humid RIF, daily fluid loss is frequent, as previously observed in rugby union (11) and sevens (23) players.
During the day of RIF, a progressive dehydration occurs (42, 43) which explains higher plasma sodium and potassium concentrations recorded at 07:00 A.M. compared to 05:00 P.M. in amateur footballers (28).
Some physically active men train at night during RIF to minimize the fluids losses that would occur if training was conducted during the day (44). This effective strategy is supported by the results of Trabelsi et al. (15) who reported that serum sodium, potassium and chloride concentrations are maintained during RIF if long-duration training was scheduled after the break of the fast; although an increase in chloride and sodium concentrations was reported if the same training was performed before the Iftar meal.
However, both training at night or during the day induce increases in some serum electrolytes at the end of RIF in bodybuilders (45). These conflicting results may be explained by the fact that total water intake decreased in bodybuilders training after the break of the fast during RIF; whereas it was maintained in practitioners of long-duration exercise during the same time-of-day. It appears that resistance training athletes concentrate less on hydration than those undertaking aerobic-based training.
Regardless of training time to minimize chronic dehydration, it has been previously recommended to drink about 600 mL/h from the Iftar meal until the sleep and a supplementary 1 L at Sahour meal (46).
3.2. Renal Function Markers
Creatinine clearance, creatinine, urea and uric acid concentrations of the plasma/serum can all be used to evaluate renal function (47-49). During RIF, serum urea and creatinine increased in sedentary men that could induce kidney adaptations in physically active men and allow maintaining the concentrations of markers of renal function (40). Similarly, creatinine values did not change during RIF in elite rugby union players (50).
However, RIF of a humid and hot summer season increases creatinine, urea and uric acid concentrations (23). Additionally, increases in serum concentration of creatinine and decreases in clearance of creatinine were noticed in practitioners of long-duration exercise in a fasted (i.e., before the break of the fast) or in a fed state (i.e., after the break of the fast) during RIF (15). Furthermore, hypertrophic training program performed in a fed or in a fasted state induced an increase in creatinine values of bodybuilders who maintain their training routines during RIF (45).
RIF induces a reduction in blood concentration of glucose during the fasting day in healthy sedentary peoples (51, 52). Higher gluconeogenesis capacity could prevent the reduction in blood concentration of glucose in sportsmen despite the decrease in caloric intake during RIF (11, 23). Unchanged glycemia has been observed in recreational bodybuilders (24, 45), physically active men (13, 15) and footballers (53). In contrast, other studies have shown a decrease in blood glucose levels in runners (54-56) and football and basketball players (57).
Blood glucose levels will be affected by the time-of-day during which the sample was collected during RIF. Indeed, glycemia recorded in the afternoon (04:00 P.M.) during RIF was lower than that in the morning (09:00 A.M.) in martial arts practitioners (58). Such results suggest that the ability to complete intense physical training sessions in the afternoon may be affected by a drop in blood glucose concentrations and should be avoided. However, in some cases athletes are obliged to undertake intense training session in the daylight. Although Png and colleagues (59) concluded that ingesting food with a low glycemic index at Sahour meal has no-beneficial effect (i.e., physiological, metabolic or performance aids) during long-duration exercise realized 12 h post-prandial during RIF, a useful strategy might be that athletes should anticipate the possibility of low afternoon blood glucose by consuming low glycemic index foods at Sahour meal in order to prolong the sugars release into the blood stream (60).
3.4. Lipid Profile
The combined effect of physical activity and RIF on the lipid profile present inconclusive results. Lipid profile is highly influenced, not only by diet, but also by physical activity levels, body fat and weight, and timing of blood sampling. Nevertheless, these measures are good indices of cardiovascular health and should be reported.
It has been shown that serum total cholesterol concentrations increased in judo athletes (20); but remained unchanged in footballers (21), middle-distance runners (61), rugby union players (50) and bodybuilders (24, 45). Mobilization of body fat stores during RIF may explain the observed increases in serum concentration of high density lipoprotein cholesterol (HDL-C) in judo athletes (20), footballers (21) and rugby union players (50). In support, an increase of HDL-C in practitioners of long-duration exercise before the break of the fast (15) or resistance training (bodybuilding) either in fed or fasted state (45) during RIF has been observed. Concentrations of low density lipoprotein (LDL) cholesterol has been shown to increase during RIF in judo athletes (20). This result may be explained by the increase in the consumption of saturated fatty acids due to alteration in food choices (62).
Chaouachi et al. (20) showed that serum values of triglycerides increased at sixteen days after the commencement of RIF and then return to pre-RIF values at the end of the month in judokas. In contrast, Bouhlel and colleagues (50) showed that triglycerides increased at the end of RIF in rugby players. Other reports indicate that triglycerides concentrations do not change during RIF (15, 38, 45).
The feeding behavior that occurs during RIF may increase apolipoprotein A1 levels which may protect cardiovascular system (20, 63), although apolipoprotein B concentrations have not been shown to change (20).
Practicing physical activity during RIF can cause a myriad of modifications in some hematological and biochemical parameters reflecting changes in hydration status and impairment in renal function. However, since the reported changes in hematological and biochemical parameters are all within the normal reference ranges of the laboratory, intense physical training could be practiced safely during RIF.
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