Endocrine and Metabolic Symptoms
1 Temperature Dysregulation
Clinical Presentation.
- Inability to maintain stable body temperature
- Feeling excessively cold (cold intolerance)
- Feeling excessively hot (heat intolerance)
- Alternating between hot and cold
- Night sweats
- Chills without fever
- Inability to tolerate temperature extremes
- Worsening of symptoms in hot or cold environments
Mechanism. Temperature dysregulation reflects hypothalamic dysfunction and autonomic impairment. The hypothalamus regulates body temperature via autonomic pathways; when these are disrupted, thermoregulation fails. Additional peripheral mechanisms contribute: skin temperature circadian rhythm disruption correlates with endothelin-1 (ET-1) levels, indicating that vascular tone dysregulation — not just central autonomic failure — drives thermoregulatory symptoms (Cambras et al. 2023). ME/CFS shares multiple pathophysiological pathways with heat stroke (gut permeability, endotoxemia, endothelial dysfunction, mitochondrial impairment, HSP deficiency), meaning that environmental heat exposure in ME/CFS activates existing vulnerable pathways rather than imposing a new stressor (Stanculescu et al. 2021).
2 Excessive Thirst and Fluid Retention
Clinical Presentation.
- Polydipsia (excessive thirst)
- Dry mouth despite adequate fluid intake
- Edema (fluid retention in legs, hands, face)
- Weight fluctuations due to fluid retention
Mechanism. Excessive thirst may reflect dysregulated antidiuretic hormone (ADH/vasopressin), inadequate blood volume (hypovolemia), or mast cell mediators affecting fluid balance. Fluid retention may reflect aldosterone dysregulation or venous pooling.
3 Weight Changes
Clinical Presentation.
- Unintentional weight loss (due to reduced appetite, GI dysfunction, or hypermetabolism)
- Unintentional weight gain (due to immobility, metabolic slowing, or medication effects)
- Difficulty maintaining stable weight
- Paradoxical sarcopenic obesity: increased fat mass with reduced muscle mass despite normal or elevated BMI
Body Composition and Metabolic Consequences. Weight change in ME/CFS is not simply a matter of caloric imbalance. Both weight gain and weight loss reflect underlying pathophysiology, and standard body weight metrics such as BMI may obscure clinically meaningful body composition changes. Flores et al. (2013) found that obesity compounds functional impairment in ME/CFS, with obese patients reporting greater activity limitations, and emphasized that conventional exercise-based weight management is contraindicated due to post-exertional malaise (Flores et al. 2013). This is consistent with the fibromyalgia literature, where a meta-analysis of 58 studies confirmed that obesity worsens symptoms and weight loss improves pain, fatigue, and function (D’Onghia et al. 2021). Crawley et al. (2013) documented elevated rates of overweight and obesity in adolescents with CFS compared to controls, attributing this partly to the enforced sedentary lifestyle imposed by PEM (Crawley et al. 2013).
A particularly important pattern is sarcopenic obesity: a combination of reduced skeletal muscle mass and increased fat mass that can occur even in patients with normal BMI. Scheibenbogen et al. (2025) documented muscle atrophy and metabolic abnormalities in ME/CFS consistent with impaired protein synthesis and mitochondrial dysfunction (Scheibenbogen and Wirth 2025). This occurs because the conditions driving weight gain (immobility, metabolic dysfunction) simultaneously promote fat accumulation while the energy deficit and mitochondrial impairment reduce the capacity for muscle protein synthesis, leading to accelerated muscle wasting. Anti-catabolic nutritional strategies — protein adequacy (1.5–2.0 g/kg ideal body weight during caloric restriction (Weijs and Wolfe 2025)), HMB (which preserved lean mass during bed rest in older adults), and creatine — are discussed as potential countermeasures in Section Exercise Dose-Response in ME/CFS Is Bifurcated: Maintenance Below Threshold, Deterioration Above; however, no anti-catabolic nutritional trial has been conducted in ME/CFS specifically (Deutz et al. 2013).
Fat oxidation impairment may further entrench abnormal body composition. Maya et al. (2023) identified deficits in acyl-CoA dehydrogenase (ACAD) and carnitine palmitoyltransferase (CPT) enzymes in ME/CFS, indicating reduced capacity to oxidize fatty acids for energy (Maya et al. 2023). When the body cannot efficiently burn stored fat, adipose tissue accumulates even under caloric restriction, while muscle remains deprived of adequate fuel for maintenance. This fat oxidation impairment is discussed further in Chapter Energy Metabolism and Mitochondrial Function.
Standard caloric equations designed for healthy populations overestimate resting metabolic rate by 5–32% in spinal cord injury populations (Alazzam et al. 2023); the degree of overestimation applicable to ME/CFS is unknown but likely falls within this range for severely immobile patients. This overestimation, combined with appetite dysregulation (Chapter Endocrine and Metabolic Dysfunction), may inadvertently promote positive energy balance — which paradoxically accelerates muscle atrophy during immobility (Biolo et al. 2008). Practical weight management strategies adapted to ME/CFS constraints are discussed in Section Weight Management in ME/CFS.
Conventional weight management recommendations—increased physical activity combined with caloric restriction—are contraindicated in ME/CFS. Exercise-based interventions risk triggering post-exertional malaise and worsening disease course. Dietary restriction without attention to nutrient density may exacerbate the mitochondrial and metabolic deficits already present. Moreover, standard caloric equations overestimate energy needs by 15–30% in moderate-to-severe disease (Alazzam et al. 2023), creating inadvertent overfeeding — which paradoxically accelerates muscle atrophy during immobility (Biolo et al. 2008). Patients and clinicians should focus on metabolic support (adequate protein intake, micronutrient repletion, orthostatic management) rather than naive caloric or activity targets.
4 Glucose Metabolism Abnormalities
Clinical Presentation.
- Hypoglycemia-like symptoms (shakiness, tremor, brain fog, fatigue) even with normal blood glucose
- Reactive hypoglycemia after meals
- Carbohydrate cravings
- Blood sugar instability
Mechanism. While blood glucose may be normal, ME/CFS patients experience subjective hypoglycemia because cells cannot efficiently convert glucose into ATP. The experience is similar to true hypoglycemia (cellular energy crisis) but the mechanism differs (fuel conversion failure rather than fuel lack).