Intermittent fasting and bone health: a bone of contention?

Abstract

Intermittent fasting (IF) is a promising strategy for weight loss and improving metabolic health, but its effects on bone health are less clear. This review aims to summarize and critically evaluate the preclinical and clinical evidence on IF regimes (the 5:2 diet, alternate-day fasting [ADF] and time-restricted eating/feeding [TRE/TRF]) and bone health outcomes. Animal studies have utilised IF alongside other dietary practices known to elicit detrimental effects on bone health and/or in models mimicking specific conditions, thus, findings from these studies are difficult to apply to humans. Whilst limited in scope, observational studies suggest a link between some IF practices (e.g., breakfast omission) and compromised bone health, although lack of control for confounding factors make these data difficult to interpret. Interventional studies suggest that TRE regimens practiced up to 6 months do not adversely affect bone outcomes and may even slightly protect against bone loss during modest weight loss (<5% of baseline body weight). Most studies on ADF have shown no adverse effects on bone outcomes, while no studies on the “5-2” diet have reported bone outcomes. Available interventional studies are limited by their short duration, small and diverse population samples, assessment of total body bone mass exclusively (by DXA) and inadequate control of factors that may affect bone outcomes, making the interpretation of existing data challenging. Further research is required to better characterise bone responses to various IF approaches using well-controlled protocols of sufficient duration, adequately powered to assess changes in bone outcomes, and designed to include clinically relevant bone assessments.

Nutritional therapy bridges the critical cut-off point for the closed-loop role of type 2 diabetes and bone homeostasis: A narrative review

“… Bone benefits [ 55 , 93 , 142 ]: Higher incidence of bone turnover markers and accelerated bone renewal; Lack of protein, calcium, vitamin D and other nutrients that maintain bone mass and density: Low bioavailability and need for higher intake to maintain bone health; The anti-inflammatory and antioxidant effects of the surplus components have positive effects on calcium absorption and bone metabolism. Intermittent fasting Fasting methods [ 143 , 144 ]: Time-restricted eating: Eating only during specific periods (4–12h) in 1 day, with overnight fasting extended for at least 12h. Alternate-day fasting: 1 day of fasting alternating with 1 day of casual or adequate eating (<25% energy expenditure).…”

“… Regular fasting: 2 days per week of fasting (25 per cent of energy consumption) and the remaining 5 days of free-feeding. Bone benefits [ 144 ]: The net effect of metabolic changes induced by lifestyle/behavioral changes on bone outcomes is unclear; Reduced energy intake and weight loss may have a negative impact on bones; Indirect negative impact on bones as a result of the independent effect of reduced physical activity; The contribution of compositional changes in muscle, fat, and bone to bone effects is uncertain; Frequent metabolic shifts cause acute insulin resistance at the first meal after fasting Low concentrations of C-terminal cross-linking telopeptide of type I collagen and OCN, gastrointestinal hormones (GPI, GLP-1) affect bone health by enhancing insulin secretion; Focus on time constraints rather than quality and quantity of food; Increased gut microbial abundance positively affects bone by influencing metabolite (SCFAs, etc.) production, improving nutrient bioavailability, and modulating immune hormones; Time-restricted eating induced changes in circadian rhythms are indirectly associated with improved bone outcomes.…”

“…A study held by Clayton DJ et al found that short-term 24-h strict energy restriction did not affect bone resorption or bone formation markers [ 163 ]. An RCT showed that a time-restricted eating program for up to 6 months was effective in reducing body weight and showed some bone protection, while an alternate-day fasting program had no adverse effects on bone [ 144 ], which were confirmed in an RCT of a 6-week time-restricted eating program in older adults, which was safe, well tolerated and did not affect lean body mass, bone density or nutrient intake [ 164 ]. In contrast, the Muslim month of Ramadan, a one-month Time-restricted eating program, has been shown to be beneficial to bone health, as dietary changes during Ramadan result in reduced mean PTH levels [ 165 ].…”

Time-Restricted Eating and Bone Health: A Systematic Review with Meta-Analysis

“…Regarding weight loss interventions based on dietary strategies, caloric restriction and intermittent fasting (IF) are common approaches to reducing energy intake that have shown effectiveness on weight loss and cardiometabolic-related outcomes [ 16 ]. Despite this, epidemiological evidence that considers breakfast omission as IF is associated with bone loss [ 17 ], and caloric restriction alone or in combination with exercise has been shown to reduce bone mass and negatively affect bone microstructure [ 18 , 19 , 20 , 21 ]. These negative effects could be caused by mechanical unloading, nutrient deficiencies, and endocrine changes caused by a low energy intake [ 22 , 23 ].…”