Intermittent fasting has become one of the most popular health strategies of the past decade, and for good reason. In younger and middle-aged adults, compressing the eating window has been linked to better insulin sensitivity, lower inflammation, modest weight loss, and improvements in cardiometabolic risk factors. Much of that evidence is genuinely encouraging.
But a new report in the Journal of Internal Medicine asks a question most fasting articles skip: does the same advice hold up at 75, 80, or 85 years old? After following nearly 3,000 older adults in Stockholm for 15 years, the researchers found that those with the longest daily gaps between meals developed chronic diseases faster than those who ate on a more conventional schedule. The effect was concentrated almost entirely in one group: adults aged 78 and older.
This study is worth understanding carefully, because it neither condemns fasting nor confirms it. It draws a line based on age.
What the researchers actually measured
The data come from the Swedish National study on Aging and Care in Kungsholmen, a long-running population study of randomly selected adults aged 60 and older. Researchers collected baseline information between 2001 and 2004, then re-examined participants repeatedly over roughly 15 years. The final analysis included 2,981 people with an average starting age of 74 years, and about 64% were women.
Here is the most important detail, and the one most likely to be lost in headlines. The investigators did not study people who had chosen a fasting protocol. They calculated the longest gap between any two eating occasions in a 24-hour day, using detailed food frequency questionnaires that asked about up to eight eating events, including snacks and drinks. That number is simply an observed eating pattern, not a deliberate practice. A person who skipped breakfast because of poor appetite and a person following a disciplined 16:8 protocol would look identical in this dataset.
Participants were divided into four groups by the length of that gap: 6-11.5 hours (the comparison group), 11.5-12.75 hours, 12.75-14 hours, and 14-24 hours. Researchers tracked health outcomes as the total number of chronic conditions a person had, drawn from a validated list of 60 disease categories confirmed through physician examinations, medical records, laboratory measures, medication use, and the national patient register. The researchers then measured how fast new conditions accumulated each year.
What they found
Compared with the shortest-gap group, participants in the 14-24 hour group accumulated chronic diseases at a meaningfully faster annual rate. In plain terms, the difference amounts to roughly one and a half to two additional chronic conditions over the full 15-year follow-up. Each additional hour of habitual fasting was associated with a small but consistent increase in that rate.
When the analysis was broken down by organ system, cardiovascular and neuropsychiatric conditions drove the finding. Musculoskeletal disease showed no consistent relationship.
The age split is the headline. Among participants aged 78 and older, longer eating gaps were clearly associated with faster disease accumulation. Among those younger than 78, the association essentially disappeared, and the estimate for the longest-fasting group actually pointed slightly in the opposite direction without reaching significance. The authors tested the durability of their findings across 21 different sensitivity analyses, including removing people with cognitive impairment or dementia, excluding those who died early in follow-up, adjusting for frailty and functional status, and accounting for the number of medications. The pattern held.
Why age might change the equation
The paper offers several plausible biological explanations, and each reflects how the aging body handles nutrition differently than a younger one.
Absorption capacity declines with age. Reduced stomach acid production and lower pancreatic enzyme activity impair uptake of vitamin B12, folate, calcium, and iron. Add delayed gastric emptying, altered motility, and shifts in the gut microbiome, and the same plate of food yields less usable nutrition. Compress the eating window on top of that, and small deficits can compound quietly over years.
Protein timing matters more in later life. Older muscle responds less efficiently to dietary protein, a phenomenon called anabolic resistance. Long fasting windows reduce opportunities to stimulate muscle protein synthesis and make it harder to distribute protein evenly across the day, both of which have been linked to lower muscle mass. Because sarcopenia is tied to cardiovascular disease, metabolic disorders, and cognitive decline, this offers a direct route from a long fasting window to accumulating chronic illness.
Metabolic flexibility narrows. Age-related declines in insulin sensitivity, beta cell responsiveness, and skeletal muscle glucose uptake may leave older adults more vulnerable to blood sugar swings during extended fasts.
Medications complicate the picture. Many commonly prescribed drugs require food for proper absorption or to limit side effects, and older adults carry the heaviest medication burden of any age group. Long gaps without food can interfere with those requirements.
What this study cannot tell you
Honest interpretation requires naming the limits, and the authors are candid about them.
This is observational research, so it demonstrates association, not causation. Reverse causation is a real possibility: people may eat less often because they are already sick, have lost their appetite, or are physically limited. The researchers worked hard to address this by adjusting for frailty, functional dependence, reduced food intake, formal and informal caregiving, and by excluding people who died early, and the results held. Still, the concern remains.
The comparison group is not what most people picture. A 6-11.5 hour gap between meals reflects ordinary meal spacing, not a fasting protocol. In fact, more than three-quarters of participants had gaps longer than 11.5 hours, which the authors note is simply typical overnight eating behavior in Sweden.
The people with the longest gaps also differed in many other ways at the start. They ate fewer meals per day, skipped breakfast far more often, had lower diet quality, lower total energy and protein intake, exercised less, took more medications, lived alone more often, and were already carrying more chronic conditions. Statistical adjustment can reduce this kind of confounding, but not eliminate it entirely.
Finally, this was a predominantly highly educated, urban, community-dwelling Swedish population. Other studies point in other directions. A cross-sectional Italian study found that early dinners combined with an overnight fast of roughly 17.5 hours was a common pattern among people who reached extreme old age.
The practical takeaway
For patients in their 60s and early 70s who are metabolically healthy, active, well-nourished, and eating adequate protein, this study offers no reason to abandon a time-restricted eating pattern that is working well.
For adults approaching or past their late 70s, especially those who are frail, underweight, taking multiple medications, losing muscle, or eating poorly to begin with, the calculus shifts. In that setting, a long daily gap without food is far more likely to represent a nutritional gap than a metabolic advantage. The priority becomes adequate protein spread across the day, sufficient calories, nutrient density, and consistency rather than restriction.
The wisest reading of this paper is that a strategy is not good or bad in isolation. It is good or bad for a particular body at a particular stage of life. The same 16-hour fast that sharpens metabolism at 55 may quietly erode muscle and micronutrient status at 82. Stewardship of the body we have been given means paying attention to which season we are in, and adjusting accordingly.
If you are over 75 and currently practicing extended fasting, this is worth discussing with your physician, particularly a review of your protein intake, body composition, medications, and nutrient status. This article is educational and is not a substitute for individualized medical advice.
