Why people quit tracking
People don't quit because they stop caring. They quit because logging is a chore. In a 24-week weight-loss study, participants spent 23 minutes a day on self-monitoring in month one, and only 65% were still recording anything by month six (Harvey et al., Obesity 2019). In another study, fewer than half were still tracking after week 10 (Turner-McGrievy et al., JMIR mHealth). Lapsed users describe journaling as "too much effort" and "tedious" (Cordeiro et al., CHI 2015).
Most of that time goes to the app, not the food: open it, search a database, pick between twelve near-identical entries, guess a serving size, repeat for every ingredient. Nexus removes that part. The chat you already have open does the estimating.
Say it like you'd say it to a friend
Had 2 rotis, dal and a small bowl of curd for lunch. Log it.
That's the whole interaction. ChatGPT or Claude works out the calories, protein, carbs, fat and fiber, then calls Nexus to save the meal. One message can hold a whole day: breakfast, a snack, a workout and this morning's weight all go in one call.
Take a picture and log it
Snap your plate with the ChatGPT camera, add a few words if you want ("ate half of this"), send. The assistant reads the photo, works out the portions and Nexus saves the result. Packaged food? Photograph the nutrition label: it's the exact numbers a barcode scanner would look up, read straight off the box (why you don't need a barcode scanner). Ate out? Photograph the bill and the assistant looks up the restaurant's published nutrition (snap the bill, log the meal).
In MyFitnessPal, Cronometer and Lose It!, photo logging sits behind a paid plan. In Nexus it is just a message. See Nexus as a MyFitnessPal alternative.
Talk instead of typing
Tap the mic in the ChatGPT or Claude composer and dictate the meal. Or stay in a ChatGPT voice conversation and say what you ate while you walk back from lunch; the assistant logs it through Nexus without you looking at a screen.
The card is where you fix things
After each log, Nexus shows your day as an interactive card: calories and protein against your goals, every meal and set listed. Tap a meal to change its calories or protein. Tap a set to change the weight or reps. Type this morning's weight and it saves when you leave the field. No re-prompting, no "actually make that 250".
Chat is great at estimating and bad at small edits. A card is the opposite. Nexus gives you both, so a wrong guess costs one tap, not a new conversation. You can also try the card yourself, with no account, in the sandbox.
It remembers, so the chat doesn't have to
Chat history scrolls away and memory is fuzzy. Nexus is a real log with dates, ids and totals. Ask "how much protein have I had this week?" or "what did I bench last Tuesday?" in any new conversation and the answer comes from what you logged, not from what the model remembers.
Workouts too
Ask for a workout and you get a page you can follow at the gym: exercises with illustrations, target weights from your history, a tick for every set. Tap Finish and the sets you did become your workout log. Already trained? Just say what you did.
More than 200 exercises have their own illustrations. Your previous session for each lift shows next to today's sets, so progress is visible without a spreadsheet.
Works where you already are
- ChatGPT: listed in the ChatGPT plugin directory. Add it once and use it on iPhone, Android, web and desktop.
- Claude: listed in the Claude connectors directory. Same account, same log.
- Anything that speaks MCP: Codex, Claude Code and other agents connect to the same server. There is also a command-line tool.
Log breakfast in ChatGPT on your phone and ask Claude about it on your laptop. It is one log. There is no separate Nexus app to install, and no new habit beyond the chat you already open every day.
Don't use ChatGPT much?
You don't need to be a power user. The ChatGPT and Claude apps are free, and opening one takes the same tap as opening a calorie app. The difference is what happens next: one sentence instead of a search box, a serving-size picker and a confirm screen. Once logging lives there, you'll find yourself asking it the next question too ("what should I eat for dinner with 600 calories left?"), with your real day as context.
How accurate is it?
Researchers who tested ChatGPT and Claude on food photos found them as accurate as traditional hand-kept food diaries, with none of the effort, and that was with 2024 models (the study, and what it means). Add a word about portion size, photograph labels and bills, tap to fix anything, and you're closer to exact than most people ever get by hand.
What it costs
Free. Photo and voice logging included, where most calorie apps put them behind a paid plan.
Check it yourself
Don't take this page's word for it. The sandbox runs the production tools and the real card with no sign-in, and any assistant can test it with plain URLs or MCP. When you're ready, add Nexus to ChatGPT or Claude.