{"id":10705,"date":"2023-08-14T06:00:25","date_gmt":"2023-08-14T05:00:25","guid":{"rendered":"https:\/\/blogs.bmj.com\/bjsm\/?p=10705"},"modified":"2023-08-21T15:41:16","modified_gmt":"2023-08-21T14:41:16","slug":"a-bad-situation-made-worse-low-carbohydrate-intake-amplifies-low-energy-availability-hormonal-disturbances","status":"publish","type":"post","link":"https:\/\/blogs.bmj.com\/bjsm\/2023\/08\/14\/a-bad-situation-made-worse-low-carbohydrate-intake-amplifies-low-energy-availability-hormonal-disturbances\/","title":{"rendered":"A Bad Situation Made Worse: Low Carbohydrate Intake Amplifies Low Energy Availability Hormonal Disturbances"},"content":{"rendered":"

Hypothetical Model for REDs Endocrine Disruptions<\/h1>\n

Introduction<\/h3>\n

Persistent or severe low energy availability (<\/span>what is termed <\/span>\u2018problematic\u2019 LEA) places an athlete at risk for the development of Relative Energy Deficiency in Sports (REDs) which compromises both their health and performance capacity <\/span>(1)<\/span>. Studies indicate LEA\/REDs are associated with hormonal disturbances in male and female athletes (1). These disturbances are especially noted in the reproductive sex steroid hormones (i.e., reduced levels of testosterone [T], oestradiol-\u03b2-17 [E<\/span>2<\/span>], and progesterone [P<\/span>4<\/span>]) (2). Additionally, evidence supports the development of low triiodothyronine (T<\/span>3<\/span>) profiles in LEA\/REDs athletes (2,3). Recent work suggests the presence of low carbohydrate (LCHO) intake coupled with LEA exacerbates the likelihood of REDs symptoms <\/span>developing<\/span> (1,4). <\/span>This blog presents a hypothetical model of how LCHO dietary intake and LEA interact to create an amplification of the endocrine dysfunctions associated with REDs<\/span><\/p>\n

What’s Carbohydrates Endocrine Connection?<\/h3>\n

Over 40 years ago Galbo et al. demonstrated that as little as four days of a low carbohydrate diet intensified the exercise cortisol response (5). Cortisol, whilst an essential hormone in the human <\/span>internal milieu<\/span><\/i>, has a cascading series of direct-indirect agonist-antagonist detrimental actions on other hormones (6,7). Figure 1 shows a hypothetical model of some of the hormone interactions and the effects of cortisol exposure.\u00a0<\/span><\/p>\n

Chronic Repetitive exposure<\/h3>\n

Researchers often <\/span>assume persistent, chronic exposure to a hormone such as cortisol, is necessary to invoke the changes demonstrated in Figure 1. <\/span>In actual fact, this <\/span>is only one scenario. Elite and semi-elite athletes train almost daily and <\/span>often<\/span> have multiple sessions per day. Most such training sessions will invoke repetitive exposures to elevated cortisol levels (albeit transient, proportional to training intensity, and can approach supraphysiological levels) (8). These <\/span>frequent <\/span>exposures to daily cortisol elevations can potentially have an additive effect similar to that of chronic elevations (6,9,10).<\/span><\/p>\n

Figure 1.<\/b> Hypothetical model of how low energy availability (LEA) plus low carbohydrate intake creates an amplification effect on creating a hormonal profile associated with problematic LEA and Relative Energy Deficiency in Sports (REDs) (16).<\/span><\/h6>\n

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Criticality of Triiodothyronine (T3)<\/h3>\n

In the model depicted in Figure 1, T<\/span>3<\/span> plays a critical role due to its permissive actions <\/span>(i.e., helping in the function of other hormones) <\/span>(11). The reduction of T<\/span>3<\/span> driven by LEA (<\/span>N.B.,<\/span><\/i> caloric restriction\/reduction suppresses T<\/span>3<\/span>) is intensified by cortisol activation of the 5\u2019deiodinase enzyme activity resulting in the prohormone thyroxine and T<\/span>3<\/span> conversion to inactive metabolites, principally 3,3′,5′-triiodothyronine (reverseT<\/span>3<\/span> [rT<\/span>3<\/span>]) (11). The lack of T<\/span>3<\/span>, <\/span>which functionally is more bioactive (i.e., brings about changes in tissues)<\/span>, leads to the amplification of T, E<\/span>2<\/span>, and P<\/span>4<\/span> reductions <\/span>already occurring due to the regulatory axis controlling their production being disrupted (see Figure 1 and Table 1 [HPG Axis]). These key reproductive hormones are <\/span>further compromised via cortiso<\/span>l’s<\/span> direct inhibition of <\/span>their production (steroidogenesis inhibition) <\/span>as well as <\/span>its <\/span>similar <\/span>inhibitory<\/span> actions on leptin and insulin (7, 11-14). Additionally, while cortisol and growth hormone (GH) linkage is complicated, glucocorticoids such as cortisol can inhibit somatostatin (GH inhibiting hormone) gene expression and <\/span>cause <\/span>circulating GH <\/span>to increase <\/span>as well as subsequently <\/span>leading to altered<\/span> insulin-like growth factor (IGF) levels (15).<\/span><\/p>\n

Conclusions<\/h3>\n

In their excellent review article, Elliott-Sale and associates summarized the endocrine profiles of female and male athletes with LEA\/REDs (2). Table 1 presents a summary of their key findings. While the model presented in Figure 1 does not capture all facets of the hormonal changes reported by these authors, it does represent the major ones generally <\/span>reported<\/span> in REDs literature (1).\u00a0<\/span><\/p>\n

Table 1.<\/b> Summary of the hormonal changes associated with low energy availability and Relative Energy Deficiency in Sports (REDs) as reported by Elliott-Sale et al. (2). Legend: <\/span>\u21d3<\/b> = decrease, <\/span>\u21d1<\/b> = increase, <\/span>\u21d4<\/b> = no change. Abbreviations: HPG = hypothalamic-pituitary-gonadal, FSH = follicle-stimulating hormones, LH = luteinizing hormone, HPA = hypothalamic-pituitary-adrenal, <\/span>HPT = hypothalamic-pituitary-thyroid<\/span>,\u00a0 TSH = thyroid stimulating hormone, T3 = triiodothyronine, T4 = thyroxine, GH = growth hormone, IGF = insulin-like growth factor, PPY = peptide YY, <\/span>RMR = resting metabolic rate (non-hormonal measure) (2).<\/span><\/h6>\n

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There are two key <\/span>take-home message<\/span>s here: <\/span>\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/h5>\n