Four popular photo-based calorie-tracking apps underestimated calories and fat by about one-third when compared with carefully prepared meals, according to findings presented at the American Society for Nutrition’s NUTRITION 2026 meeting.
Researchers tested four photo-based calorie-tracking apps—MyFitnessPal, LoseIt!, Cal AI and Appediet—against 102 precisely prepared meals made in a controlled metabolic kitchen at the U.S. National Institutes of Health, according to a news release from the American Society for Nutrition.
In the test, the apps’ estimates were substantially lower than the meals’ known nutrition values. On average, the apps underestimated calories by roughly 250 to 345 calories and underestimated fat by about 30 grams.
Aaron Hengist, a postdoctoral visiting fellow with the Intramural Program of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) at NIH, urged users not to rely on photo-based estimates alone.
"People using a photo-based tracking app without adjusting the portions or entering the amounts of food should take the results with a grain of salt," Hengist said. "These apps tend to underestimate calories, especially from fats, so what they actually ate is likely higher than what the app shows."
The findings were presented by Olivia Charles, a postbaccalaureate intramural research training fellow at NIDDK, during the President’s Oral Session at NUTRITION 2026, the society said. The meeting was held July 25–28 in National Harbor, Maryland, just outside Washington, D.C.
The research team also reported early, preliminary results from follow-up testing of more than 200 additional meals, suggesting the apps may have greater difficulty estimating low-carbohydrate ketogenic meals, which are typically higher in fat.
The researchers recommended pairing photo-based tools with more traditional tracking approaches—such as adjusting portions or entering amounts—to improve accuracy in real-world use.
