Current study was purposed to assess plant-based dietary indices in male footballers and healthy non-athlete controls, and also their associations with urinary oxidative biomarkers. The findings indicated that PDI was higher in footballers. Furthermore, a negative association between PDI and F2a-IP was shown in all participants, and others did not show statically significant relationships.
The Academy of Nutrition and Dietetics, the American College of Sports Medicine, and Dietitians of Canada have concluded that “well-chosen nutrition strategies can enhance the performance of, and recovery from, sporting activities”[32]. As mentioned earlier, plant-based nutrition is a growing trend among athletes not only for the health advantages, but also for enhancement in athletic performance [33], in justification of which it can be said that plant-based dietary patterns may offer following effects; role in cardiovascular health, a leaner body mass, facility glycogen storage, delay fatigue, reduced OS, reduced inflammation, reduced blood viscosity, and increased tissue oxygenation [22, 23].
Current study showed that footballer group had significantly higher PDI score in comparison to non-athlete group, but no significant differences were shown in hPDI and uPDI scores between the two groups. Wirnitzer et al. stated that exercise alone is not enough for health and exercise performance, beside healthy diet-at best whole food vegan diet- is critical for this purpose. Therefore, the integration of a healthy diet- and a regular exercise program into the athlete’s daily schedule, can offer the most promising intervention for optimizing their health and performance [34]. In a cohort study over a 12-years period, it has been demonstrated that greater increase in PDI score over study period was correlated with an increase in physical activity, and also lower risk of all-cause mortality [35]. Footballers were more adherent to PDI than non-athletes, and also in terms of PDI components, the intake of healthy-based plant foods such as vegetables, nuts, and fruits was significantly higher in footballers. Vegetables, whole grains, fruits, and beans tend to be high in minerals, vitamins, and fiber, very low in saturated fatty acids, and devoid of cholesterol [22]. In addition, total fat, and animal fat intake of footballers were lower. Hinton et al. illustrated that more intake of dietary fat could be related to cognitive difficulties in former football players, thus they suggested the encouragement of football players to adherence to a healthy dietary habits [36]. Fuhrman et al. study recommended both vegan and non-vegan athletes to intake more beans, nuts, seeds, greens, whole grains, and other colorful plant products, to maximize their performance, endurance and resistance to illness, and also their recovery [37].
While several studies demonstrated that plant-based diets may provide benefits for athletes, some studies stated that vegetarian diet is not superior to omnivores diet in terms of augmenting health, performance, and fitness [38, 39]. Lynch et al. claimed that despite differences in nutrient intake, plasma carnitine and creatine in vegetarians compared to omnivores, there is no difference in exercise performance [40]. As a result, it is likely that following a plant-based diet may be a healthful option for athletes such as footballers, but further investigation is required to be investigated the effects of plant-based diets on sports performance. It is noteworthy that with any dietary regimen, nutrient adequacy is a critical consideration [22], therefore, any athlete who follows a plant-based diet should be supervised by a registered dietitian with a background in sport nutrition to ensure optimal nutrient and energy intake [38].
In the present study a significant and negative association between PDI and F2a-IP was observed in all participants. Even though more and more athletes have increasingly been adopting plant-based diets, its relation with OS is not well understood, especially in footballers. A systematic review study by Aleksandrova et al. revealed that diets with high intake of vegetables and fruits, the Dietary Approaches to Stop Hypertension (DASH) diet, and Mediterranean diet can lead to lower levels of F2a-IP [41]. Further, Dietrich et al. observed vegans illustrated lower excretion levels of F2a-IP than omnivores. Also held an inverse correlation between vegan diet and OS measured by malondialdehyde, 8-OHdG and F2a-IP [19]. A study by Griffiths et al. indicated that more adherence to critical points of Mediterranean diet, such as more consumption of vegetables, exerted positive effects on OS and inflammation [42].
The influence of plant-based diets on anti-oxidative properties, seems to be due to the high concentration of polyphenols and antioxidants found in this dietary patterns [33, 43]. Moreover, aforementioned compounds may enhance the delivery of oxygen and nutrients to cells and removing metabolic by-products through augmenting vessel diameter and improving blood flow [44, 45]. People following plant-based dietary patterns, such as vegetarianism and veganism, which intakes more amounts of vitamin E, vitamin C, beta-carotene, polyphenols, and other antioxidants, may have a superior antioxidant status, and subsequently better management of OS [46–49]. However, mentioned information is based on the assumption that the intake of antioxidants compounds is higher in vegetarians compared to omnivores [50].
Tomey et al. reported an inverse relationship between three vegetable components (lutein, beta-carotene, and lycopene) and F2a-IP concentration in midlife women. Chemical structure of mentioned molecules can lead to decreased peroxidation, due to the double bonds on the polyene chains, which play roll in oxidation/reduction reactions [51]. Likewise, Block et al. revealed a negative correlation between beta-carotene and plasma level of F2a-IP in healthy adults [52].
In addition to mentioned compounds, other dietary factors such as dietary fats could be related to F2a-IP. Dietary fats may indeed affect directly or indirectly the levels of F2a-IP, as they 1) are the main substrates of F2a-IP production, 2) influence the plasma concentrations of F2a-IP transporters, and 3) alter the tissue’s fatty acid composition [53]. Although the precise effect of dietary fats on F2a-IP levels in different populations still requires more research, it has been indicated that some specific fatty acids, such as trans-fatty acids (TFA) may increase F2a-IP excretion in healthy adult individuals [53–55]. TFA can incorporate into cellular membrane’s phospholipids and reduced cell membrane fluidity via displacing cis-polyunsaturated fatty acids, leading to more activity of free radicals in the phospholipids, and subsequently exacerbating oxidative damages [56].
As TFA are present in plant-based foods less than animal-based foods [57], it is likely that the higher the PDI is, the lower the intake of TFA, which they may lead to lower formation of F2a-IP. Tomey et al. cohort study held a positive association between TFA intake and the urine F2a-IP concentration in women [51]. In addition, in other studies in healthy men and women, TFA enhanced urinary F2a-IP levels [58, 59]. Moreover, in vivo investigations it has been confirmed that more intake of TFA is associated with higher urinary F2a-IP levels [60]. Altogether, it is likely that through more intakes of plant-based foods, the body's oxidant status may be improved, and then formation of F2a-IP may be decreased.
As positive remarks, to our knowledge, this is the first study that evaluated PDI and its relationship with urinary 8-OHdG and F2a-IP concentrations in footballers, also a valid and reliable FFQ was applied to assess food intake. As a limitation, inferring the mechanisms of the results is impossible due to the cross-sectional design of this research. F2a-IP levels categorized as < 0.86 ng/mg creatinine and ≥ 0.86 ng/mg creatinine are considered low and high, respectively [61]. In our study F2a-IP levels in all participants are classified as low (0.12 ng/mg creatinine in footballer group, and 0.24 ng/mg creatinine in non-athlete group). Although even at this level, a relationship between plant-based diet score and OS was observed, further researches are needed to ascertain if this association exists at different OS levels.