Zomato founder Deepinder Goyal has defended his much-discussed Temple wearable against doctors questioning its scientific foundation, saying he has invested millions of dollars in developing the technology. However, as the Rs 85,000 device enters the Indian market, experts say its biggest challenge is proving that it can accurately measure what it claims.
In a post on X addressed to “concerned Indian doctors”, Goyal said Temple’s development cost around $30 million, with $20 million coming from his personal funds. He rejected suggestions that the venture was designed to make quick money and highlighted its 14-day, no-questions-asked return policy.
“If the product doesn’t work, it fails out of the gate and the company dies before recovering a tenth of its R&D,” he wrote.
Goyal also said the company would make its claims independently verifiable as more people began using the device. He indicated that pre-print research papers would be released before peer-reviewed publications and that independent studies would follow.
However, doctors say the central issue is not the investment behind Temple or its hardware but whether its technology has been scientifically validated.
What Does Deepinder Goyal’s Temple Wearable Claim to Do?
Temple is a forehead-worn wearable developed under Goyal’s health-tech venture. Unlike conventional smartwatches that primarily track heart rate, sleep and physical activity, it claims to monitor changes in blood flow and oxygenation in the brain.
Its proprietary BrainFlow metric is designed to provide insights into cerebral circulation. Another measurement, called Entropy, is presented as a real-time score indicating how hard the body is working to sustain itself.
Ranging from 1 to 250, Entropy is influenced by factors such as sleep, exercise, stress, food, caffeine and meditation. Goyal has described it as a measure of real-time energy expenditure, with potential applications in fitness, recovery and longevity.
The device is also associated with his Gravity Ageing Hypothesis, which proposes that gravity and prolonged periods spent upright may influence blood circulation to the brain and contribute to ageing.
Pre-orders in India opened on November 1, with Temple priced at Rs 85,000. Each unit is made to order, and delivery is expected within approximately three months. The product is positioned as a wellness and research device rather than a medical diagnostic tool.
Doctors Question the Science Behind Entropy
Neurologists have questioned whether Entropy can be considered a scientifically established biomarker.
Hyderabad-based neurologist Dr Sudhir Kumar previously described the idea as intriguing but said the available evidence did not establish its validity. He argued that observing changes in a reading during exercise or stress does not prove that it reliably measures metabolism, biological ageing or longevity.
He also pointed to the absence of publicly available information about the metric’s biological basis, calculation methodology and independent validation.
Neurologist Dr Rahul Chawla had similarly called for more details about the technology and the research behind it, saying that the available information was insufficient to assess its claims.
Doctors say the crucial questions include whether Entropy measures a clearly defined biological process, whether it performs consistently across individuals and whether it provides useful information beyond existing health metrics.
Can Temple Actually Measure Blood Flow to the Brain?
Another major concern involves Temple’s headline BrainFlow claim.
The device uses optical sensors based on photoplethysmography (PPG), positioned over the superficial temporal artery in the forehead. This artery supplies blood to the scalp and face, while the brain receives its primary blood supply through the internal carotid and vertebral arteries.
Dr Navin Gnanasekaran, head of clinical services for radiology and interventional radiology at Apollo Hospitals, Chennai, has questioned whether measurements from superficial blood vessels can establish what is happening inside the brain.
For example, exercise increases blood flow to the skin and scalp as the body attempts to regulate temperature. A forehead sensor may detect these changes, but they do not necessarily indicate corresponding changes in cerebral circulation.
He has also questioned whether correlations between Temple readings and clinical transcranial Doppler measurements prove that the wearable directly measures brain blood flow. Correlation during major physiological changes, he argues, does not establish direct measurement.
Gravity Ageing Hypothesis Faces Further Questions
Temple’s broader longevity claims have also attracted scrutiny. The Gravity Ageing Hypothesis suggests that prolonged exposure to gravity while standing upright could gradually affect blood supply to the brain.
However, doctors point to cerebral autoregulation, the body’s mechanism for maintaining relatively stable brain blood flow despite changes in posture and blood pressure.
Dr Gnanasekaran has also cautioned against treating inversion practices as a solution, particularly for older people and those with conditions such as hypertension or glaucoma, as inversion may increase pressure inside the eyes and skull.
Experts acknowledge that Temple could have practical uses as a wearable, including potentially tracking heart rate during intense exercise. But that would be different from proving its ability to measure cerebral blood flow or assess biological ageing.
As Goyal promises further research, doctors say the device’s credibility will ultimately depend on transparent methods, rigorous clinical validation, peer-reviewed studies and independent replication.
