You snap a photo of your lunch, the app spits out a number, and you log it without thinking twice.
For millions of people trying to lose weight or manage diabetes, that number sets the day.
A new analysis from the National Institutes of Health suggests the number may be far off.
The AI photo features in four popular tracking apps underestimated meal calories by about a third, in results not yet peer reviewed.
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Researchers at the National Institute of Diabetes and Digestive and Kidney Diseases presented the finding at the American Society for Nutrition's NUTRITION 2026 meeting in July, according to EurekAlert.
They prepared 102 meals in a controlled metabolic kitchen, weighing every ingredient to 0.1 gram.
Then they ran photos through MyFitnessPal, Lose It!, Cal AI, and Appediet, and compared each app's estimate to the actual nutrient content.
How far off each app was
Across the four apps, the AI photo features missed by about 250 to 345 calories per meal. Appediet came closest.
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Cal AI landed furthest off, with MyFitnessPal and Lose It! in between.
Fat was the bigger problem. All four apps missed about 30 grams of fat per meal on average.
Fat carries more than twice the calories of protein or carbohydrate, and it is often invisible in a photo. Think oil in a pan, butter on toast, dressing on a salad.
Carbohydrates were the most consistent of the three macronutrients across all four apps.
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The team then tested more than 200 additional meals and found the apps struggled most with high-fat, low-carb meals.
Weight loss and diabetes tracking
A 300-calorie gap is not small. Over a day of three logged meals, that is close to 900 calories a person never recorded.
Someone eating a reported 1,800 calories a day to lose weight may be closer to 2,700. That can explain stalled weight loss on an app that looks perfect on paper.
The gap matters even more for people on a ketogenic diet or managing blood sugar.
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The researchers found the apps misread high-fat meals the most, exactly the pattern many people with type 2 diabetes are told to follow.
Aaron Hengist, a postdoctoral fellow at the NIDDK, said in the press release that people using a photo-based tracking app without adjusting portions should take the results with a grain of salt.
A simple fix that cuts the error
The study only looked at the apps' automatic photo features. Most of these apps also let users enter food quantities by hand or scan barcodes, which pulls from standard nutrition databases rather than image analysis.
Weighing one or two higher-fat items, like oil, nuts, or cheese, and entering them manually closes much of the gap.
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A free alternative is the US Department of Agriculture's FoodData Central database, which gives verified nutrient values for tens of thousands of foods.
The abstract was presented in the President's Oral Session at NUTRITION 2026 in National Harbor, Maryland, and a full peer-reviewed paper has not yet been published.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.