Samsung's Galaxy Watch 8 antioxidant sensor proves surprisingly useful for diet tracking

Samsung's Galaxy Watch 8 comes with a feature that most other smartwatches don't have: the ability to measure the antioxidants in your body by pressing your thumb against the watch face. The sensor reads carotenoids—the pigments that make carrots orange, tomatoes red, and spinach green—which accumulate in your skin and serve as a proxy for how much fruit and vegetables you're actually eating. It's a clever bit of engineering, but the real question is whether it works.

The reviewer started skeptical, especially after the watch told them their antioxidant levels were "Low." Rather than dismiss the reading, they decided to test it: spend a week eating as many carotenoid-rich foods as possible and see if the watch could detect the difference. The premise is straightforward. Carotenoids are one type of antioxidant—compounds that counteract oxidative stress from smoking, drinking, overeating, and chronic stress. The WHO recommends 400 grams of fruits and vegetables daily. Samsung's watch is designed to tell you, without any manual food logging, whether you're hitting that target.

Here's how it works: the Galaxy Watch 8's optical sensors detect carotenoids stored in your skin. You press your thumb against the sensor, which pushes blood away from the measurement area, allowing the multicolored LEDs to get a clean reading. Samsung calibrated the scoring system using clinical trials at Samsung Seoul Hospital, correlating fruit and vegetable intake with carotenoid accumulation. A score of 75 to 100 means you're meeting recommendations. Between 50 and 75 means you're getting 50 to 99 percent of what you should. Below 50 is critically low. The company also notes that stress, smoking, and drinking can tank your score, making this as much a lifestyle tracker as a nutrition one.

The reviewer started at 53—meaning they were consuming about 56 percent of the recommended daily amount. Over the next week, they loaded up on salads, bell peppers, cantaloupe, and other produce. They discovered something important along the way: raw vegetables are high in fiber and vitamins but low in beta-carotenes. Cooked vegetables paired with healthy fats—oil, meat, peanut butter—deliver far more carotenoids to your body. By day seven, their score had climbed to 65, representing 80 percent of recommended intake. The watch had detected a real dietary shift. Samsung says it can take up to two weeks for the full effect to show, and the trajectory suggested one more week of eating well would push the score to the target of 75.

But there's a catch. Carotenoids are just one type of antioxidant. Flavonoids, polyphenols, and lycopene—found in beans, teas, and countless other foods—are equally important for fighting free radicals and slowing aging. The Galaxy Watch 8 can't measure these because they don't have the pigmentation that makes carotenoids visible to optical sensors. So while the watch gave the reviewer useful feedback about one dimension of their diet, it was missing the full picture. A person eating tons of antioxidant-rich foods that don't contain carotenoids would get no credit from the watch, even though they're doing themselves real good.

The reviewer appreciated having a tool that didn't require obsessive food logging—a feature that appeals to people who care about eating well but hate calorie counting. The antioxidant index proved responsive enough to validate real dietary changes. But it's important to understand its limits. The watch isn't lying when it says your antioxidant levels are low; it's just measuring one piece of a much larger puzzle. The real value isn't in hitting a perfect score on Samsung's scale. It's in having a baseline, noticing when you slip, and using that feedback to make better choices. Everything else—all the antioxidants the watch can't see—is just extra credit.