Although several studies have indicated intermittent fasting (IF) promotes weight loss and improves metabolic health, its effect on bone health is unclear. Recently, scientists reviewed existing literature and summarized the effect of varied forms of IF, such as the 5:2 diet, alternate day fasting (ADF), and time-restricted eating/feeding (TRE/TRF), on bone health.
In this study, the authors obtained relevant articles from the MEDLINE database until the 30th of September 2022. The impact of IF on bone health was assessed based on animal studies and human observational and interventional studies in adult populations.
Impact of Intermittent Fasting on Human Health
Although fasting has been practiced for centuries during religious events, such as Ramadan, short-term fasting is a relatively new phenomenon. This type of fasting is also known as IF, which started being practiced in the last decade. It is an unconventional approach to improving metabolic health and promoting weight loss.
IF has quickly become popular for reduced calorie consumption. A recent survey showed that in the US, one in four Americans consider using or have tried IF. In addition, several studies on IF revealed that it substantially improves insulin sensitivity and blood lipid profile and lowers blood pressure.
Compared to traditional fasting, IF is associated with daily energy restriction. In this case, complete or substantial energy restriction occurs within a specific timeframe, after which adequate or ad libitum eating is permitted.
Bone Health Assessment Tools and Techniques
It is important to determine the impact of IF on other body systems, such as the skeletal system. Weight loss is associated with a reduction in bone mass which might affect bone microstructure. Bone mass or density, strength, and structure could be analyzed using biomarkers, bone measurements, or surrogate endpoints.
Dual-energy X-ray absorptiometry (DXA) is a common technique used to determine bone mineral content (BMC) and areal bone mineral density (aBMD). Peripheral quantitative computed tomography (pQCT) is another technique used to measure bone geometry and volumetric BMD (vBMD). Bone turnover markers (BTMs) are used to assess the changes in bone formation and bone resorption rates.
Animal studies have been conducted to understand the effect of IF on bone health. These studies have revealed that IF, in addition to a high-fat or ketogenic diet, negatively affected bone health. The effect of a ketogenic diet with or without ADF was studied using a rat model. This study showed that rats subjected to ADF and a ketogenic diet exhibited inhibition in osteoclast proliferation and osteogenic differentiation.
Compared to the control group of rats subjected to a regular diet, rats under the ADF ketogenic diet showed decreased bone strength and poor overall bone health. In addition, the control group possessed reduced bone resorption and higher bone formation markers levels compared to the rats under the daily ketogenic diet and ADF ketogenic diet. Furthermore, TRF that involved three hours of feeding per day for 4 weeks showed reduced femoral BMD. Hence, TRF was found unable to protect bones from adverse effects. In contrast, TRE regimes practiced for a relatively short period of up to six months did not show any adverse effects on bone.
Not many observational studies related to the effect of IF on bone health were found. However, one cross-sectional analysis revealed no significant changes in lumber spine BMD or total body BMC in healthy adults following ADF and in those who followed a regular diet.
Another cross-sectional analysis indicated that young women who skipped breakfast around three times per week had lower hip BMD than those who consumed breakfast daily. A longitudinal study observed that young men who skipped breakfast almost every day had a higher chance of experiencing bone loss in the lumbar spine than those who consumed breakfast daily.
The current understanding of the effect of IF on bone health is limited due to a lack of adequate evidence. The current trials have short durations ranging between three and six weeks, and trial duration is important because it affects body weight and metabolic and skeletal effects. Therefore, in the future, longer trial durations are required to assess how IF affects bone during weight loss properly.
The majority of studies have analyzed regional BMC/BMD considering the total body DXA assessments. They have failed to conduct scans at clinically relevant sites, such as the lumbar spine and hips. These studies have not investigated the effect of IF on bone microstructure or fracture risks. These shortcomings in existing research must be rectified in the future.
Since most available studies included small sample size, they failed to determine the statistically significant difference in bone parameters. In addition, the authors pointed out the scarcity of research assessing the effects of IF regimens on bone outcomes in vulnerable groups, such as elderly and postmenopausal women.