Most people learn about their health through occasional doctor visits and yearly blood tests. These checks are useful, but they capture only what is happening at one moment.
Researchers at the National University of Singapore are exploring a different idea: health may be better understood by watching how the body changes and recovers every day.
The project, called DELTA, is unusually personal. Professor Dean Ho, director of the Institute for Digital Medicine at the Yong Loo Lin School of Medicine, National University of Singapore, served as the only participant.
His research team continuously tracked his body while changing his eating, exercise, fasting, and sleep routines.
The idea behind DELTA is that every person has a biological starting point, but that starting point is not fixed. Sleep, stress, food, exercise, illness, age, and other factors can shift how the body works from day to day. Even the same person may respond differently to the same challenge at different times.
Ho began the project in August 2024, and the study is continuing. For about eight months, he wore three consumer devices: a Whoop tracker, a Garmin device, and an Apple Watch. These provided repeated information about measures such as heart rate, activity, recovery, and sleep.
The team also introduced demanding lifestyle changes. Ho often fasted for about 20 hours a day and completed several 48-hour fasts. Each morning he performed about 90 minutes of strength or cardiovascular exercise.
His diet emphasized leafy vegetables, seeds, olive oil, lean protein, and other foods commonly associated with a Mediterranean-style eating pattern. Drinks were largely limited to water, electrolytes, black coffee, and black tea without milk or sugar. This was a tightly controlled personal experiment rather than a general lifestyle program designed for the public.
One major focus was metabolic flexibility. The body normally uses both carbohydrates and fat for energy, changing the balance depending on whether a person has recently eaten, is fasting, or is exercising. Researchers wanted to measure how quickly Ho could shift from mainly using sugar toward using stored fat.
According to the study, his switching time improved during the project. It initially took more than 24 hours and later fell to about 16.5 hours. The researchers viewed faster switching as a sign that his metabolism had become more responsive to changes in energy supply.
The study also reported a large change in resting heart rate. Ho’s resting rate fell from about 65 beats per minute to 46. A lower resting heart rate can occur as cardiovascular fitness improves, although the meaning of any heart-rate value depends on the individual and should be interpreted in the context of symptoms, medications, and overall health.
Sleep changed substantially as well. Ho shifted from going to sleep after midnight to going to bed at around 9 p.m. His reported sleep duration increased from roughly five hours to almost eight hours, with more deep sleep and less time awake during the night.
The researchers also examined his gut microbiome, the large community of microbes living in the digestive system.
They reported favorable changes during the study, including no detectable Fusobacterium in the measurements described. The data also suggested changes related to how efficiently the body conserved energy during some fasting periods.
A custom artificial intelligence system was used to combine the large amount of information. The researchers described it as a healthspan copilot designed to measure how the body responds to and recovers from stress. The system estimated Ho’s biological age at about 32 even though he was 47.
Biological age is an attempt to describe how old the body appears based on biological measurements rather than years since birth. Many biological-age systems use a single set of blood, genetic, or physiological measurements. The DELTA researchers argue that watching how quickly the body responds and recovers may provide additional information about healthy aging.
This idea of resilience is central to the project. Two people can have similar test results on a normal day but respond very differently to fasting, exercise, poor sleep, or other challenges. Measuring the speed and quality of recovery could potentially reveal information that a routine annual check misses.
The study was published in PLOS One and builds on earlier work involving Ho that appeared in PNAS Nexus in 2024. The researchers hope the approach will eventually help people use their own long-term health data to make more individualized decisions instead of following the same lifestyle plan as everyone else.
The project is scientifically interesting because it demonstrates how dense, continuous measurements can reveal changes that ordinary health checks cannot. Tracking one person repeatedly can provide an extremely detailed view of that individual and can help researchers develop new questions, measurement methods, and technology. It is particularly useful as an exploratory experiment.
But the study has an obvious and very important limitation: it involved only one person, who was also the senior researcher leading the work. The findings cannot show that the same fasting, exercise, or dietary routine would produce similar results in other people. They also cannot separate with certainty which part of the program caused each change because many lifestyle factors changed together.
The biological-age estimate should also be interpreted cautiously. Saying that a 47-year-old has a biological age of 32 does not mean the person has literally reversed 15 years of aging. Such estimates depend on the measurements and mathematical model used, and their ability to predict long-term health outcomes still needs validation.
The fasting and exercise schedule was also unusually intensive. Fasting for 20 hours regularly, completing 48-hour fasts, and exercising for 90 minutes every morning may not be suitable or safe for everyone, particularly people with certain medical conditions, people taking some medicines, older adults, pregnant people, or those with a history of eating disorders. The study should not be treated as instructions for copying Ho’s routine.
Overall, DELTA is best viewed as a demonstration of what highly personalized health tracking might make possible rather than proof of a new longevity formula. Its strongest contribution is the idea that health is dynamic and that recovery from challenges may reveal information hidden between routine checkups.
Larger studies involving diverse participants will be needed to determine whether these measurements can reliably predict healthier aging or help people live longer.
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