A Short-Term Ketogenic Diet Impairs Markers of Bone Health in Response to Exercise.

To investigate diet-exercise interactions related to bone markers in elite endurance athletes after a 3.5-week ketogenic low-carbohydrate, high-fat (LCHF) diet and subsequent restoration of carbohydrate (CHO) feeding. World-class race walkers (25 male, 5 female) completed 3.5-weeks of energy-matched (220 kJ·kg·d) high CHO (HCHO; 8.6 g·kg·d CHO, 2.1 g·kg·d protein, 1.2 g·kg·d fat) or LCHF (0.5 g·kg·d CHO, 2.1 g·kg·d protein, 75-80% of energy from fat) diet followed by acute CHO restoration. Serum markers of bone breakdown (cross-linked C-terminal telopeptide of type I collagen, CTX), formation (procollagen 1 N-terminal propeptide, P1NP) and metabolism (osteocalcin, OC) were assessed at rest (fasting and 2 h post meal) and after exercise (0 and 3 h) at Baseline, after the 3.5-week intervention (Adaptation) and after acute CHO feeding (Restoration). After Adaptation, LCHF increased fasting CTX concentrations above Baseline ( = 0.007, Cohen's = 0.69), while P1NP ( < 0.001, = 0.99) and OC ( < 0.001, = 1.39) levels decreased. Post-exercise, LCHF increased CTX concentrations above Baseline ( = 0.001, = 1.67) and above HCHO ( < 0.001, = 0.62), while P1NP ( < 0.001, = 0.85) and OC concentrations decreased ( < 0.001, = 0.99) during exercise. Exercise-related area under curve (AUC) for CTX was increased by LCHF after Adaptation ( = 0.001, = 1.52), with decreases in P1NP ( < 0.001, = 1.27) and OC ( < 0.001, = 2.0). CHO restoration recovered post-exercise CTX and CTX exercise-related AUC, while concentrations and exercise-related AUC for P1NP and OC remained suppressed for LCHF ( = 1.000 compared to Adaptation). Markers of bone modeling/remodeling were impaired after short-term LCHF diet, and only a marker of resorption recovered after acute CHO restoration. Long-term studies of the effects of LCHF on bone health are warranted.