Introduction 

Population aging is accompanied by an increasing burden of chronic diseases and multimorbidity. Age is a major risk factor for diseases affecting multiple organ systems, while the proportion of older adults worldwide continues to increase.1,2 Multimorbidity, commonly defined as the coexistence of two or more chronic conditions, affects a substantial proportion of adults aged ≥60 years and is associated with functional decline, reduced independence, psychological distress, and increased mortality.3-5 These trends have intensified interest in lifestyle interventions that can simultaneously address metabolic health and promote healthy aging. 

Nutrition is an important modifiable determinant of chronic disease risk and healthy aging.6 In addition to what and how much people eat, increasing evidence suggests that when food is consumed may influence metabolic health. Intermittent fasting (IF), including time-restricted eating (TRE), involves alternating periods of eating and fasting and has been associated with improvements in body weight, insulin sensitivity, and several cardiometabolic risk factors.7,8 However, the applicability and safety of prolonged fasting in older adults remain uncertain. 

Intermittent fasting and metabolic health 

IF encompasses several dietary approaches, including TRE, alternate-day fasting, and periodic energy restriction. TRE is characterized by limiting daily food consumption to a predefined window, often resulting in a fasting period of approximately 14–16 hours. During fasting, metabolic switching from glucose toward greater fatty-acid utilization may occur, accompanied by changes in insulin signaling, cellular stress responses, and other metabolic pathways.7,8 

Evidence from clinical trials suggests that IF can produce modest reductions in body weight and adiposity and may improve glucose regulation and blood pressure. However, many studies have been conducted in younger or middle-aged adults with overweight or obesity, and interventions have generally been short in duration.8,9 Therefore, whether these metabolic benefits translate into improved long-term health outcomes in older adults remains unclear. 

Evidence in older adults 

The potential benefits of fasting in older adults require careful consideration because aging is accompanied by physiological changes that may alter the response to energy restriction. Older individuals are at increased risk of sarcopenia, frailty, malnutrition, and unintentional weight loss. Consequently, a dietary intervention that reduces energy intake may have different consequences in an older adult than in a younger person with obesity. 

Recent evidence suggests that moderate IF may have favorable effects on body composition in middle-aged and older adults without major short-term reductions in fat-free mass.9 However, the evidence remains limited regarding skeletal muscle strength, physical performance, frailty, and long-term functional outcomes. Preservation of muscle mass and function is particularly important in older adults because loss of muscle strength is strongly associated with falls, disability, hospitalization, and mortality. 

Observational data suggest that the relationship between fasting duration and health outcomes may not be linear. Zhang et al. reported that among adults aged ≥60 years, habitual fasting for >12.4 hours was associated with increased cardiovascular mortality, whereas a fasting duration of approximately 11.5 hours was associated with the lowest overall mortality.10 These findings raise the possibility that prolonged fasting may not necessarily provide additional benefits in later life. However, because the study was observational, residual confounding and reverse causation cannot be excluded. 

Potential risks of prolonged fasting 

Longer fasting periods may be problematic for older adults who already have inadequate nutritional intake. Reduced appetite, dental problems, gastrointestinal disorders, swallowing difficulties, polypharmacy, and chronic diseases can make it challenging to consume sufficient calories and protein within a restricted eating window. In individuals with frailty or sarcopenia, further reductions in energy or protein intake could potentially accelerate muscle loss. 

Observational studies have also linked longer habitual fasting intervals in community-dwelling older adults with unfavorable metabolic biomarkers and poorer physical function.11 These findings contrast with some short-term intervention studies reporting metabolic benefits from TRE, emphasizing the importance of distinguishing between controlled dietary interventions and habitual prolonged fasting. 

The potential risks are particularly relevant in adults with diabetes receiving glucose-lowering medications, because prolonged fasting can increase the risk of hypoglycemia. Older adults taking multiple medications may also require adjustment of medication timing when meal patterns change. Thus, IF should not be regarded as a universally appropriate dietary intervention for all older individuals. 

Younger-old versus older-old adults 

Older adults are a heterogeneous population, and the effects of fasting may differ substantially according to age, frailty, nutritional status, and comorbidity burden. A healthy 60-year-old with obesity and preserved muscle function may respond differently to IF than an 80- or 90-year-old with frailty, sarcopenia, or multimorbidity. 

The distinction between the younger-old and older-old is therefore clinically important. Although younger-old adults may potentially derive metabolic benefits from moderate fasting, the oldest adults may be more vulnerable to inadequate energy and protein intake. Current evidence is insufficient to determine whether fasting recommendations should differ across these age groups.9,12 

Future studies should specifically examine whether fasting duration modifies outcomes according to age and functional status. Trials should include clinically meaningful measures such as appendicular muscle mass, handgrip strength, gait speed, physical performance, frailty, nutritional status, and quality of life rather than relying solely on body weight and metabolic biomarkers. 

Clinical implications 

The available evidence suggests that moderate, individualized meal-timing interventions may be more appropriate than prolonged fasting for many older adults. When IF is considered, attention should be given to maintaining adequate total energy and protein intake, hydration, and nutrient density. Resistance exercise and adequate protein consumption may also help preserve muscle during weight-loss interventions. 

IF should be approached particularly cautiously in individuals with frailty, sarcopenia, undernutrition, unintended weight loss, advanced age, or multiple medications. In patients with diabetes or other conditions in which meal timing affects medication safety, fasting should be undertaken with appropriate clinical supervision. 

Importantly, the available evidence does not establish that longer fasting is better. A recent systematic review emphasized that although IF may provide metabolic benefits, evidence for long-term health outcomes remains limited and excessive fasting may carry potential risks.12 

Conclusion 

Intermittent fasting is an increasingly studied dietary strategy with potential benefits for body weight and cardiometabolic health. However, evidence in older adults remains limited and heterogeneous. While moderate fasting regimens may provide metabolic benefits, prolonged fasting could pose nutritional and functional risks, particularly among frail or nutritionally vulnerable individuals. 

Future research should move beyond weight loss and metabolic biomarkers to evaluate muscle preservation, physical function, frailty, cognition, quality of life, and mortality. Importantly, studies should distinguish between younger-old and older-old adults because the balance between metabolic benefit and nutritional risk may change substantially with advancing age. Until more robust long-term evidence becomes available, fasting in older adults should be individualized, nutritionally adequate, and focused on preserving functional independence. 

References 

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2. United Nations, Department of Economic and Social Affairs, Population Division. World Population Ageing 2020 Highlights. New York: United Nations; 2020. 
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9. Santero S, Blagojević BD, Merzah M, Celada Guerrero JA, Cena H, Ordovas JM, et al. Intermittent fasting and fat-free mass outcomes in middle-aged and older adults: a scoping review. Adv Nutr. 2026;17(7):100663. 
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12. Santero S, Blagojević BD, Merzah M, Celada Guerrero JA, Cena H, Ordovas JM, et al. Intermittent fasting and healthy aging in older adults: a systematic review of cardiometabolic, mental health and cognitive outcomes with a network meta-analysis of anthropometric measures. Nutrients. 2026;18(9):1450.