Studies are needed into the long-term effects of the ketogenic diet on bone health, according to Australian researchers who found adverse effects on bone modelling in athletes who followed a low carb diet for a few weeks.
A study involving world-class race walkers (25 male, 5 female) at the Australian Institute of Sport assessed the short term effects of a ketogenic low-carbohydrate, high-fat (LCHF) diet compared to a high carb diet on 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) .
It found that after 3.5 weeks of the ketogenic diet, fasting CTX concentrations increased significantly while P1NP and OC levels decreased.
Similarly, post-exercise CTX concentrations increased significantly in the ketogenic diet intervention group, and were above those seen in a high carbohydrate diet group. P1NP and OC concentrations decreased during exercise.
Exercise-related area under curve (AUC) for CTX was increased by LCHF after the ketogenic diet, with decreases in P1NP and OC.
Some of the ketogenic diet-related changes in bone markers were not reversed in a subsequnt 3.5 week period of carbohydrate restoration. Exercise-related AUC for P1NP and OC remained suppressed, while post-exercise CTX concentrations and CTX exercise-related AUC recovered.
The researchers said a catabolic effect of low carbohydrate intake on bone could be explained by previous studies showing that endurance exercise with low glycogen availability stimulates the release of the cytokine interleukin-6 (IL-6) from the exercising muscles.
They noted that IL-6 has been hypothesized to lead to enhanced activity of the receptor activator of the nuclear factor K B-ligand, which controls bone turnover by increasing osteoclastic activity, thereby increasing bone breakdown.
“Our data reveal novel and robust evidence of acute and likely negative effects on the bone modeling/remodelling process in elite athletes after a short-term ketogenic LCHF diet, including increased marker of resorption (at rest and post-exercise) and decreased formation (at rest and across exercise), with only partial recovery of these effects following acute restoration of CHO availability.”
“Long-term effects of such alterations remain unknown, but may be detrimental to bone mineral density (BMD) and bone strength, with major consequences to health and performance,” they added.
“Given the injury risks and long-term outcomes underpinned by poor bone health in later life, in athletes as well as individuals who undertake exercise for health benefits, additional investigations of the ketogenic diet and its role in perturbing bone metabolism are warranted.”
The findings are published in Frontiers in Endocrinology.