Photo-based calorie-tracking apps may underestimate energy in meals

Thanks to advances in AI, popular calorie-tracking apps can now use a photo of a meal to estimate the nutritional content of what you’re eating. Although these apps are convenient, a new study found that four photo-based apps underestimated the calorie and fat content of meals by about a third.

Photo-based calorie tracking uses AI image recognition to identify foods in a meal photo and estimate portion sizes. This information is then compared with nutrition databases to calculate estimated calories and nutrients.

“Photo-based calorie tracking apps are very popular, especially for people trying to manage their health or lose weight,” said Aaron Hengist, a postdoctoral visiting fellow with the Intramural Program of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. “However, the accuracy of many of these apps has not been thoroughly evaluated. Our study helps address this question by looking at whether these apps can reliably estimate calories.”

Olivia Charles, a postbaccalaureate intramural research training fellow at NIDDK, will present the findings at NUTRITION 2026, the annual meeting of the American Society for Nutrition, held July 25–28 in National Harbor, Maryland, just outside Washington, D.C.

The new research is part of a larger diet study at the NIH Clinical Center examining how the body processes nutrients when a person eats a low-carbohydrate (ketogenic) or standard diet. Meals for this clinical trial are prepared in a controlled metabolic kitchen, a type of research kitchen where ingredients are carefully weighed to the nearest 0.1 gram.

To evaluate how well photo-based calorie-tracking apps estimate nutritional content from images, the researchers acquired standardized photos of 102 meals prepared as part of the diet study and then ran them through the MyFitnessPal, LoseIt!, CalAI and Appediet apps.

“By using meals prepared in a tightly controlled metabolic kitchen, we were able to compare the apps’ estimates against a precise reference,” said Hengist. “This kind of direct, high-quality comparison hasn’t been available before.”

All four apps underestimated the calorie content of meals by an average of 250 to 345 calories and fat content by about 30 grams. The analysis also showed that the MyFitnessPal and LoseIt! apps estimated the energy content of higher-calorie meals more accurately than lower-calorie meals and that all four apps estimated carbohydrates more consistently than other macronutrients.

“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,” said Hengist. “These apps tend to underestimate calories, especially from fats, so what they actually ate is likely higher than what the app shows.”

After performing the initial analysis, the researchers examined more than 200 additional meals to better understand what might affect the accuracy of the apps. Their early results suggest that the apps struggle more with meals that are part of a low-carb ketogenic diet, likely because the higher fat content of these meals tends to be consistently underestimated.

The investigators say that combining photo-based features with more traditional methods of measuring diet quality could improve the real-world accuracy of calorie-tracking apps.

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Swati Mestri

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Robert Egan

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