Long fasting windows in older patients tied to accelerated disease

Clinical takeaway: Ask when older patients eat, not just what. A habitual gap of 13 hours or more tracked with faster accumulation of chronic conditions in the oldest patients, and may signal appetite loss or food access issues. 

Intermittent fasting is the new keto diet, pitched as an optimal, trendy way to help keep weight under control. In younger populations, compressing the eating window produces modest weight loss and better cardiometabolic markers, enough that the practice has drifted into general nutrition advice. But almost all of the evidence to support potential health benefits and safety has come from young and middle-aged populations.

Multimorbidity is the default state of later life, affecting more than half of adults age 60 and older, and the rate at which conditions accumulate tracks with functional decline, loss of independence, and mortality. Diet is one of the few modifiable inputs into that trajectory, which is why meal timing has drawn interest as a low-cost lever. But in older patients, a long gap between meals is not always a choice. It can reflect appetite loss, medication effects, living alone, or the practical difficulty of preparing food, and none of those are visible unless you ask. 

Participants with the longest habitual gaps between meals, 14 to 24 hours, accumulated chronic conditions faster than those with the shortest gaps, 6 to 11.5 hours. The difference worked out to roughly one additional condition per decade. The pattern was graded rather than threshold-driven. Even the 12.75 to 14 hour group accumulated faster than the reference group, meaning the signal was not confined to extreme fasting. 

A gap of roughly 13 hours is what many patients reach by finishing dinner at 7 and eating breakfast at 8. Each additional hour of fasting tracked with a small, consistent increase. Adjustment for diet quality, energy intake, protein intake, and reduced food consumption barely moved the estimates. 

Among participants 78 and older, the longest fasters added new conditions at about one per decade above the reference group. Every additional hour tracked with a measurable increase in that group. Among those under 78, the estimate sat at zero. Longer gaps tracked with no faster accumulation at all in the younger patients, and the difference between the two age groups was itself statistically significant. By organ system, the faster accumulation concentrated in neuropsychiatric conditions. In patients 78 and older, musculoskeletal and cardiovascular disease did not play a role. 

Researchers drew on the Swedish National study on Aging and Care in Kungsholmen, a population-based cohort of 2,981 community-dwelling adults age 60 and older, followed up to 15 years. Habitual fasting duration came from a food frequency questionnaire asking when participants typically ate across a 24-hour period, defined as the longest gap between any two eating occasions. Chronic conditions were counted from physician assessments, medical records, and the national patient register. 

The mechanisms that make fasting tolerable in midlife weaken with age, the authors argue. Micronutrient absorption declines, older muscle responds less efficiently to dietary protein, and many common drugs assume food arrives on a predictable schedule. The study could not separate chosen fasting from meals missed because of illness or appetite loss, though adjusting for frailty and functional dependence did not weaken the association. 

"Much of the research on fasting has been conducted in younger or middle-aged populations. Our findings suggest that the associations may be different in older adults, particularly among the oldest age groups," said Adrián Carballo Casla, postdoctoral researcher at the Aging Research Center, Karolinska Institutet. 

Source: Kalmbach L, et al. (2026 Aug 20) J Intern Med. Habitual fasting duration and accelerated multimorbidity in older adults