Although several studies have indicated that intermittent fasting (IF) promotes weight loss and improves metabolic health, its effect on bone health is unclear. Scientists recently reviewed the existing literature and summarized the effect of various forms of IF, such as the 5:2 diet, alternate day fasting (ADF), and time-restricted feeding/feeding (TRE/TRF), on the bone health. This review is available at he british nutrition magazine.
In this study, the authors obtained relevant articles from the MEDLINE database up to September 30, 2022. The impact of IF on bone health was evaluated based on animal studies and human observational and interventional studies in adult populations. .
Accepted manuscript: Intermittent fasting and bone health: a bone of contention? Image Credit: Kattecat / Shutterstock
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 fast is also known as IF, which began to be practiced in the last decade. It’s an unconventional approach to improving metabolic health and promoting weight loss.
IF has quickly become popular for its reduced calorie intake. A recent survey showed that in the US, one in four Americans are considering using or have tried FI. In addition, several studies on FI have revealed that it substantially improves insulin sensitivity and blood lipid profile, and reduces blood pressure.
Compared to traditional fasting, IF is associated with daily energy restriction. In this case, the total or substantial energy restriction occurs within a specified period of time, after which the ad libitum eating is allowed.
Bone Health Assessment Tools and Techniques
It is important to determine the impact of FI on other body systems, such as the skeletal system. Weight loss is associated with a reduction in bone mass that can 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 changes in rates of bone formation and resorption.
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 affects 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 put on a normal diet, rats given the ADF ketogenic diet showed decreased bone strength and poor overall bone health. Furthermore, the control group possessed reduced bone resorption and higher levels of bone formation markers compared to rats on the daily ketogenic diet and the ADF ketogenic diet. Additionally, TRF involving three hours of feeding per day for 4 weeks showed reduced femoral BMD. Therefore, it was found that TRF could not protect bones from adverse effects. By contrast, ERT regimens practiced over 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, a cross-sectional analysis revealed no significant changes in lumbar spine BMD or total body BMC in healthy adults after ADF and in those who followed a regular diet.
Another cross-sectional analysis indicated that young women who skipped breakfast about three times per week had lower hip BMD than those who ate breakfast daily. A longitudinal study found that young men who skipped breakfast nearly every day were more likely to experience bone loss in the lumbar spine than those who ate breakfast daily.
Limitations in Understanding the Effect of FI on Bone Health
Current understanding of the effect of IF on bone health is limited due to a lack of adequate evidence. Current trials have short durations ranging from three to 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 adequately assess how IF affects bone during weight loss.
Most studies have analyzed regional BMC/BMD taking whole body DXA assessments into account. They have been unable to perform scans in 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 deficiencies in existing research need to be corrected in the future.
Since most of the available studies included a small sample size, they failed to determine the statistically significant difference in bone parameters. In addition, the authors noted the paucity of research evaluating the effects of IF regimens on bone outcomes in vulnerable groups, such as the elderly and postmenopausal women.