New Study Finds Age When Intermittent Fasting May Stop Helping

Intermittent fasting has become one of the most popular health strategies of the past decade. Millions of people have adopted it for weight loss, better blood sugar control, and hopes of a longer life. But a large new study tracking older adults for 15 years delivers a sobering message: for people in their late 70s and beyond, going long stretches without eating is linked to a faster buildup of chronic diseases, not a slower one.

Researchers reporting in the Journal of Internal Medicine followed nearly 3,000 adults aged 60 and older in Stockholm, Sweden, tracking how long they typically went between meals and how many chronic health conditions they developed over time. What they found runs counter to the fasting narrative that has taken hold in popular health culture. Older adults who habitually went the longest between meals, anywhere from 14 to 24 hours, accumulated chronic diseases faster than those who ate more frequently throughout the day. That pattern showed up in adults aged 78 and older but not in younger adults, suggesting that the risks of long fasting gaps may grow sharper the older a person gets.

For a population already juggling multiple health conditions, that finding carries real weight. More than half of adults aged 60 and older are already living with multiple chronic diseases at the same time, according to the researchers. Adding more conditions faster means more medications, more doctor visits, more loss of independence, and a greater risk of early death. If longer gaps between meals are contributing to that for the very old, it matters.

How This Fasting Study Worked

Data came from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), an ongoing long-term study of randomly selected adults aged 60 and older in Stockholm. Baseline data were collected between 2001 and 2004, with a 73% response rate. After excluding participants without meal-timing information, the final group included 2,981 people. Participants were followed for an average of about 7 years, though disease data stretched up to 15 years across six waves of follow-up. Adults under 78 were checked in every six years, while those 78 and older were assessed every three years to keep up with faster changes in health.

Participants reported their typical eating schedule over the previous year, noting when they usually ate breakfast, lunch, dinner, and any snacks in between. From that information, researchers calculated each person’s longest typical gap between any two eating occasions in a 24-hour window. Participants were grouped into four roughly equal categories: those fasting 6 to 11.5 hours (the reference group), 11.5 to 12.75 hours, 12.75 to 14 hours, and 14 to 24 hours.

Chronic disease burden was tracked using a system that counted conditions across 60 categories, drawn from physician assessments, medical records, lab results, and a national patient registry. Conditions were grouped into three major body systems with the biggest impact on older adults: heart and blood vessel diseases, brain and mental health diseases, and bone and joint diseases. Researchers used statistical models that accounted for repeated measurements over time and adjusted for a wide range of factors, including age, sex, education, living situation, social support, smoking, physical activity, sleep quality, overall diet quality, calorie intake, and protein intake.

What the Data Showed About Fasting and Aging

Compared to those in the shortest fasting group, participants who went 14 to 24 hours between meals accumulated chronic diseases at a meaningfully faster rate over the follow-up period. Each additional hour of habitual fasting was associated with a higher yearly rate of disease accumulation. Heart and blood vessel diseases and brain and mental health diseases both showed faster accumulation in longer fasters, while bone and joint diseases did not show a consistent pattern in either direction.

When researchers split the group by age, the picture became much clearer. Among participants aged 78 and older, those in the longest fasting group accumulated total chronic diseases significantly faster than shorter fasters, and the association also held for brain and mental health conditions. Among adults younger than 78, no statistically significant association was found. The findings held up across 21 sensitivity analyses designed to test whether sick people eating less, rather than less eating making people sick, missing data, cognitive impairment, extreme calorie-reporting errors, and other potential problems distorted the results.

Why Fasting May Hit Older Bodies Differently

Researchers point to several biological realities of aging that could explain the findings. As people get older, the stomach and digestive system naturally become less efficient. The body produces less stomach acid and fewer digestive enzymes, making it harder to absorb key nutrients like vitamin B12, calcium, and iron even when adequate food is consumed. When eating is compressed into a shorter window, those already-limited absorption opportunities get squeezed further, a shortfall the researchers say could build into subtle but cumulative nutritional gaps that contribute to disease over time.

Aging also changes how muscles respond to protein from food. Older muscle tissue is less sensitive to the signals that protein normally sends to trigger repair and growth. Longer gaps between meals reduce how often those signals are sent, which the paper notes has been linked to lower muscle mass in older adults. Loss of muscle mass in aging has, in turn, been tied to worse outcomes across multiple organ systems, including heart disease and cognitive decline. Additionally, many medications commonly prescribed to older adults require food for proper absorption or to avoid side effects, and extended fasting could interfere.

“Although fasting is often promoted for metabolic health, our findings suggest that such benefits may be confined to younger individuals,” the study’s authors wrote in their conclusion.

A Caution Worth Taking Seriously

This study cannot prove that long fasting gaps directly cause faster disease accumulation. It is observational, meaning researchers tracked what people naturally did rather than assigning them to fasting or non-fasting groups. The study was also conducted in a specific population: predominantly urban, highly educated, community-dwelling older adults in Sweden. Whether these findings apply to more diverse populations or to people in different countries and healthcare systems remains an open question.

Still, the study is large, long, and rigorous in ways that are hard to dismiss. With 15 years of follow-up, nearly 3,000 participants, and results that held steady across more than 20 sensitivity analyses, the association proved consistent. At a time when fasting is routinely marketed as a near-universal health strategy, this research reminds us that age changes how the body handles food timing in ways that matter. For the very old, the wellness industry may have some catching up to do.

Disclaimer: This article summarizes findings from a single observational study and is for general informational purposes only. Because the research tracked people’s natural eating patterns rather than assigning fasting schedules, it can show an association between longer meal gaps and chronic disease but cannot prove that one causes the other. Nothing here is medical advice. Anyone considering changes to their eating schedule, especially older adults or people managing chronic conditions or medications, should consult a qualified healthcare professional.

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