The study of the interaction between intermittent anaerobic lactic exercise and fasting during the month of Ramadan is crucial for male university athletes. This period presents unique challenges in terms of nutritional management and training, with potential impacts on haematological responses to exercise.¹ Ramadan fasting involves significant dietary changes, which can affect haematological parameters. Previous research has shown varied effects on haematocrit (HCT) and haemoglobin (Hb) levels during fasting. Some studies report increases,² decreases,³ or no changes⁴ in these parameters. In addition, fasting can influence leukocyte levels and other haematological elements,^5,6 indicating complex physiological responses.

Intensive training also has substantial impacts on haematological parameters. High-intensity exercise can lead to changes in white blood cell (WBC) counts, with increases following maximal exercise and decreases following high-intensity interval training.^7,8 Endurance training is associated with a decrease in various haematological indices because of increased plasma volume.^9,10 High-intensity acute exercise can activate blood platelet (PLT) function,^{11,12,13,14,15} while regular long-term high-intensity exercise may reduce PLT activation.^13,16,17 During Ramadan, the combination of fasting and exercise can lead to specific haematological responses. Some studies suggest an acute increase in red blood cell (RBC) count because of dehydration-induced haemoconcentration,^18,19 while others find no significant changes in WBC or PLT counts.^3,16 There is a notable decrease in post-Ramadan RBC count in some cases,³ and varied responses in WBC counts following exercise.⁷ Platelet responses during Ramadan vary, with some studies observing reductions after high-intensity aerobic exercise,^10,20 and others finding stable levels.^9,21 Despite these findings, there is a lack of detailed studies specifically examining the effects of intermittent anaerobic lactic exercise during Ramadan on haematological parameters in male university athletes. This gap highlights the need for in-depth examination to understand the physiological implications during this unique period.

This study aims to evaluate the effect of intermittent anaerobic lactic exercise and Ramadan fasting on variations in haematological parameters in male university athletes. Specifically, it seeks to assess how these factors interact to influence RBC, WBC, and PLT parameters, with the goal of establishing optimal training and nutritional strategies during the month of Ramadan.

At rest, Ramadan fasting significantly altered erythrocyte-related parameters compared with normal (non-fasted) conditions (Figure 1; Appendix Table 1-A1). Red blood cell counts increased from 4.87 ± 0.51 × 10⁶/µL to 6.04 ± 1.58 × 10⁶/µL (24.02% increase; Cohen’s d = 0.99, 95% CI [0.23, 1.75]), and HCT rose from 37.80% ± 3.39% to 53.33% ± 17.91% (41.08% increase; d = 1.21, 95% CI [0.39, 2.03]; Figure 2). Conversely, Hb levels decreased from 12.98 g/dL ± 1.56 g/dL to 11.58 g/dL ± 4.84 g/dL (10.72% reduction; d = 0.79, 95% CI [0.08, 1.50]), and MCHC fell from 32.90 g/dL ± 1.52 g/dL to 30.61 g/dL ± 0.91 g/dL (6.12% reduction; d = –1.62, 95% CI [–2.32, –0.92]; Figure 2). Mean corpuscular volume and MCH also trended downward (MCV: 87.20 ± 3.97 fL vs. 84.62 ± 5.12 fL, d = –0.57, 95% CI [–1.23, 0.09]; MCH: 29.00 ± 1.76 pg vs. 25.89 ± 2.14 pg, d = –1.92, 95% CI [–2.64, –1.20]), although these fell outside conventional thresholds for significance. During Ramadan, acute intermittent anaerobic exercise further decreased RBC counts from 6.04 ± 1.58 × 10⁶/µL to 5.08 ± 1.26 × 10⁶/µL (15.89% reduction; r = 0.69, 95% CI [0.31, 0.91]), HCT from 53.33% ± 17.91% to 42.64% ± 10.71% (20.04% reduction; r = 0.82, 95% CI [0.48, 0.95]), and Hb from 15.82 g/dL ± 4.84 g/dL to 12.97 g/dL ± 3.40 g/dL (18.01% reduction; r = 0.66, 95% CI [0.28, 0.90]; Figure 2). Under normal conditions, none of these erythrocyte parameters demonstrated significant pre-post exercise shifts (all p > 0.10; | r | ≤ 0.45).

Leukocyte-related indices at rest also differed markedly between Ramadan and normal conditions. Total WBC counts declined from 7.79 ± 1.62 × 10³/µL to 5.82 ± 0.83 × 10³/µL (25.29% decrease; d = 0.12, 95% CI [–0.32, 0.56]), while Gran percentages increased from 62.81% ± 7.67% to 71.66% ± 2.58% (14.09% increase; d = 1.55, 95% CI [0.63, 2.47]; Figure 1). At the same time, lymphocyte percentages fell from 26.00% ± 8.52% to 22.87% ± 1.80% (12.04% reduction; d = –0.51, 95% CI [–1.17, 0.15]; Figure 1), and MON and NEU each showed moderate, but significant increases (MON: 4.20% ± 4.29% to 8.78% ± 6.94%, d = 0.79, 95% CI [0.08, 1.50]; NEU: 60.59% ± 9.01% to 66.59% ± 7.28%, d = 0.73, 95% CI [0.03, 1.43]). Following intermittent anaerobic exercise during Ramadan, lymphocyte percentages further increased from 22.87% ± 1.80% to 27.29% ± 2.33% (19.32% increase; r = 0.63, 95% CI [0.23, 0.88]; p = 0.046; Figure 1), whereas Gran percentages decreased from 71.66% ± 2.58% to 68.31% ± 4.00% (4.67% decrease; r = 0.90, 95% CI [0.52, 0.97]; p = 0.005; Figure 1). Under normal conditions, exercise did not produce significant changes in leukocyte or leukocyte-subpopulation percentages (all p > 0.10; | r | ≤ 0.45). All numerical values and effect-size metrics are available in Appendix 1 Table 1-A1, and graphical representations are provided in Figure 1 and Figure 2.

This study looked at changes in haematological parameters observed during the Ramadan fasting period, with significant variations recorded at rest. Figure 1 and 2 illustrates these changes, showing significant increases in Gran (14.09%; Figure 1), RBC (24.02%; Figure 2), and HCT (41.08%; Figure 2). Previous research has partly corroborated our findings. For example, the study, as demonstrated by Kasemsuk et al.²⁴ and Kilic et al.^25, also highlighted increases in HCT and RBC count during Ramadan fasting. These positive alterations could be the result of regular physical activity combined with fasting. These changes may result from haemoconcentration because of decreased water intake and increased erythropoiesis, a process stimulated by increased production of erythropoietin in response to fasting.¹⁹

In contrast, a 25.29% decrease in WBC levels was observed in our study, in agreement with the observations made by Faris et al.,²⁶ but in contradiction with the study carried out by Askari et al.²⁷ who reported an increase in the number of MON and total WBC. However, these variations are contested by Attarzadeh et al.²⁸ and Almeneessier et al.²⁹ who recorded no significant changes in WBC levels. It should also be noted that various factors, including age, diet and training status, can influence WBC concentration, particularly after exercise, highlighting the complexity of the interaction between fasting and immune responses.^30,31,32

In our study, we also observed a 10.72% decrease in Hb levels (Figure 2). This trend is in line with the results of Lamine et al.³³ who also reported a slight, but statistically insignificant drop in this parameter. Our observations regarding the reduction in Hb contrast with prior findings, such as those by Bouhlel et al.² and Maughan et al.,³ who noted stable or increased levels during Ramadan.

We also observed a 6.12% decrease in the mean corpuscular Hb concentration (Figure 2), which could be attributed to a series of physiological changes, including fluctuations in hydration levels leading to haemoconcentration,³⁴ metabolic changes mobilising the body’s energy reserves,³⁵ alterations in circadian rhythms potentially affecting Hb synthesis,³⁶ and hormonal adaptations, particularly in insulin and cortisol profiles, which can indirectly influence blood composition.^37,38 These variations were observed at complete rest before any physical exercise, suggesting that these changes could be mainly attributable to fasting.

During Ramadan, daytime fluid restriction induces a relative dehydration state. Leiper and Molla³⁴ demonstrated that morning haematological measures often reflect partial rehydration from nocturnal intake, yet residual haemoconcentration persists. In our protocol, sampling between 9:00 and 11:00 meant participants had rehydrated overnight, but could remain slightly dehydrated, explaining elevated HCT and Hb at baseline – a pattern consistent with Moussa et al.³⁹ and Chaouachi et al.⁴⁰ Adequate iron stores are crucial for maintaining Hb synthesis during caloric restriction. Bachero-Mena et al.⁴¹ and Jastrzębska et al.⁴² demonstrated that vitamin D-supplemented athletes preserve red cell parameters better under high-intensity training, pointing to micronutrient interplay. In our cohort, the decrease in MCH and MCHC despite increased RBC count (Figure 2) suggests early iron mobilisation or modest depletion, especially if nocturnal meals lacked sufficient heme iron (e.g. meat, fish) or enhancers like vitamin C. Future protocols should include ferritin and transferrin measurements to confirm iron’s role.

Regarding the effects of exercise during Ramadan fasting, our data indicate a 19.32% increase in LYMP percentages and a 4.67% decrease in Gran (Figure 1). These changes are corroborated by the existing literature (Chaouachi et al.⁴³), which reports a variable increase in LYMP in response to acute and chronic exercise during this period⁷ as well as a potential decrease in certain immune cells, including Gran.²⁷ Fasting and physical exercise can increase oxidative stress, which may lead to a modulation of Gran levels, possibly explaining the observed decrease. Intense exercise during fasting can temporarily increase the concentration of LYMP in the blood, a normal immune response to exercise, which is likely exacerbated in the presence of fasting.⁴⁴

In the present study, a significant decrease of 15.89% in erythrocyte parameters was observed (Figure 2). These results differ from those of the study by Zerguini et al.¹⁷ which reported no significant change in erythrocyte count during Ramadan fasting combined with physical activity. Several mechanisms could explain this reduction. Firstly, the increase in protein catabolism could have an influence on the erythropoietic process, as suggested by Trabelsi et al.³⁵ Secondly, the increase in oxidative stress could cause alterations to erythrocyte membranes, leading to a reduction in the number of RBC.^45,46

In our sample, significant decreases in HCT and Hb levels were recorded as 20.04% and 18.01% respectively (see Figure 2). These results are corroborated by a previous study of Tunisian footballers during Ramadan, which also documented a decrease in Hb levels.³ In contrast, work carried out by Chaouachi et al.⁴⁰ on elite judokas during the same period showed an increase in HCT levels associated with a reduction in Hb levels. Although the latter study also reported a decrease in Hb content, the concomitant rise in HCT suggests a divergence in the underlying mechanisms from those identified in our work.

The primary limitation is the small sample size (n = 10), which constrains statistical power and generalisability. We did not measure direct hydration markers (e.g. body mass change, plasma osmolarity) or iron indices (ferritin, transferrin). Future work should include a larger cohort, longitudinal tracking of iron status and direct hydration assessments to disentangle haemoconcentration from plasma volume effects.⁴⁷ Moreover, stratifying by training level (sedentary vs. moderate vs. elite) would clarify how chronic adaptation modifies haematological responses to Ramadan and exercise.

By incorporating hydration, iron status and training level considerations – alongside key literature comparisons^{7,9,18,19,24,25,40,42,44} – this discussion addresses reviewer recommendations, contextualises our findings and outlines necessary methodological refinements for future research.

Our research highlights significant changes in haematological parameters both at rest and post-exercise during Ramadan fasting.

These changes may reflect the body’s adaptation to fasting, with potential implications for immune health and erythropoietic function. Although these findings provide reliable data, further studies are needed to elucidate the mechanisms underlying these changes and to assess their clinical impact. Further investigations should also consider confounding variables such as age, diet and training status for a more nuanced understanding of these phenomena. Despite the establishment of a solid empirical base, further studies are imperative to clarify the underlying mechanisms of these variations.⁴⁸