If you are building anything that turns a photo of food into a number, this one is worth a minute.

Researchers in the intramural program of the US National Institute of Diabetes and Digestive and Kidney Diseases (NIH) cooked 102 meals in a metabolic kitchen, where the content of every plate is known. They analysed photos of each meal with the photo features of four apps and compared every estimate with the known value.

Every app came in low. Mean energy underestimate per meal:

App Underestimate 95 % CI

Appediet 252 kcal 210–295 kcal

MyFitnessPal 327 kcal 269–385 kcal

Lose It! 333 kcal 282–383 kcal

Cal AI 345 kcal 296–392 kcal

That is roughly a third of the meal missing. All four also underestimated fat, by about 30 g ; Lose It! and Cal AI underestimated carbohydrate too, by about 14 g.

The fat line is the interesting one

Thirty grams of fat is about 270 kcal on its own (9 kcal per gram, the standard Atwater factor). That is close to the whole gap.…