| King Grub |
2020-03-19 11:32 |
Inga direkta bevis.
"does energy deficiency decrease immunity and increase infection in athletes? A 25% calorie restriction, over a 2-year period in non-obese adults (BMI 25.1 kg/m2), resulted in a 10% body weight loss but did not decrease in-vivo cell-mediated immunity (skin delayed-type hypersensitivity test) or antibody responses to T- and B-cell-mediated vaccinations (hepatitis A, tetanus/diphtheria and pneumococcal); and had no effect on clinical infections [79]. On the contrary, the authors observed salubrious benefits of moderate calorie restriction, without malnutrition, on inflammation; as demonstrated by 40–50% lower circulating C-reactive protein and tumour necrosis factor-α. These inflammatory molecules have well-established roles in the pathogenesis of multiple chronic diseases and aging; as such, the findings align with the contemporary view that dietary restriction without malnutrition elicits a healthy phenotype and extends the lifespan [79,80,81]. Of course, the findings of research examining the influence of long-term moderate energy deficits on immunity in non-obese adults are interesting but arguably of limited relevance to athletic populations. For example, there are obvious population differences in body composition (average BMI of 25.1 kg/m2 is considered overweight [79]) and the energy deficit in athletic populations typically results from high energy expenditure during heavy training, rather than calorie restriction. Notwithstanding, studies in athletic and military populations investigating short-term severe energy restriction (48 h, ~ 90% restriction) and long-term moderate energy restriction during training (8 weeks, ~ 25% restriction) show only subtle and short-lived changes in immunity [82,83,84]; and no increase in the immune-modulating hormone, cortisol. Concordant with these findings, low energy availability in female and male endurance athletes has little effect on circulating cortisol [85]. This is perhaps not surprising as a recent meta-analysis showed that circulating cortisol increases in states of complete fasting but typically not during less severe energy restriction [86]. It is a common misconception, and an oversimplification, that increases in circulating cortisol always decrease immunity [87]; the reality is more nuanced. For example, increases in circulating cortisol during short-term stress (lasting minutes to hours) can have adjuvant-like effects that enhance immunity [31, 88]. In contrast, chronic stress (lasting days to months) can disrupt the cortisol circadian rhythm and increase glucocorticoid resistance, with harmful effects on immunity, inflammation and infection resistance [31, 89]. In summary, direct evidence to support the notion that energy deficiency of the magnitude often reported in elite female athletes compromises immunity is currently lacking."
https://link.springer.com/article/10...79-019-01160-3 |
