The study everyone cites
In 2025, researchers at the University of Gothenburg gave ChatGPT, Claude and Gemini 52 standardized food photos and compared their estimates with weighed reference values (Fridolfsson et al., Current Developments in Nutrition). ChatGPT and Claude landed within about 36% on energy per photo. Their conclusion:
ChatGPT and Claude achieved accuracy levels comparable with traditional self-reported dietary assessment methods but without associated user burden.
Read that again. A photo, with zero effort, did as well as the manual food diary.
The manual log was never accurate
The calorie apps' database entries look precise. What you type into them isn't. In a classic New England Journal of Medicine study, dieters who kept food records under-reported what they actually ate by 47% on average (Lichtman et al., 1992). Forgotten snacks, guessed portions, the cooking oil nobody logs. A five-decimal number from a database multiplied by a guessed serving is still a guess.
And the biggest error of all is the meal you never log because opening the app felt like work. Most people are gone from their food log within ten weeks (Turner-McGrievy et al.). Zero logged meals is 100% error.
Those were last year's models
The Gothenburg study tested GPT-4o and Claude 3.5 Sonnet, both from 2024. The models in ChatGPT and Claude today are several generations newer, with much stronger vision and the ability to search the web mid-answer. Every one of those gains reaches Nexus automatically, because Nexus uses whichever model you're already talking to.
How Nexus gets you closer to exact
The study's one consistent weakness was big portions: the models tended to under-estimate large plates. Nexus is built so you can close that gap in seconds:
- Add one sentence. "Large bowl", "cooked in butter", "I had seconds". The model uses it, and it's the difference that matters most.
- Photograph the label. For anything in a package, the nutrition panel gives the exact numbers. That's as good as a barcode, because it's the same source.
- Photograph the bill. At a chain restaurant, the assistant looks up the restaurant's own published nutrition.
- Fix it with one tap. Every meal on the Nexus card is editable. If you know better, change the number; your totals follow.
What actually moves the scale
Weight change comes from the trend over weeks, and a trend survives a meal that's off by 15%. It doesn't survive a log that stops on day eight. The tracker that wins is the one that still has entries in month three. That's the whole design of Nexus: logging is one message in a chat you already have open, so you keep doing it.
Add Nexus to ChatGPT or Claude, or try the card in the sandbox first.