Carbon deserves its reputation. Co-founded by Dr Layne Norton — a PhD in nutritional sciences with a serious evidence-based following — and registered dietitian Keith Kraker, it was one of the first apps to automate what a human macro coach does: check in weekly, compare your result to your target, and adjust your numbers. It supports cutting, gaining, maintenance and reverse dieting, offers balanced, low-carb, low-fat, keto and plant-based styles, and its annual plan is £99.99 a year in the UK — about £8.33 a month (UK App Store, August 2026).
The difference is what happens after the numbers. Carbon hands you updated targets — and, by its own design, it only adjusts them if you were compliant that week; the food itself remains your job, priced in dollars, with no trial before you pay. Fettle’s Engine works from your weekly trend even when the data is imperfect, places you in an explicit, named state — hold, adjust, diet break, protective hold — explains the decision, then finishes the job: the plan becomes meals, and the meals become a ready-to-buy grocery checkout.
Carbon prices are published US prices as of July 2026, charged in USD; sterling equivalents vary with exchange rate. We aim to keep this accurate — corrections welcome.
This is Fettle.
One-tap grocery checkout
Every change explained · no black-box coaching
Choose Carbon if…
You follow Layne Norton’s work and want his methodology in app form
You log consistently and can hold a compliant week — the algorithm rewards it
You’re happy planning and shopping for your own food
You only want the numbers — Carbon does targets and check-ins and nothing else, at the same £99.99 a year
Choose Fettle if…
You want the plan turned into meals and a filled grocery basket, not just targets
Your weeks aren’t always compliant — and you want a system built for that
You want the reasoning shown, plus protective handling of messy-data weeks
You’re in the UK and want UK foods, sterling pricing and a free first month
The short version
Carbon automates the coach’s arithmetic — credibly, and at a fair price — then hands the food problem back to you. Fettle takes the whole job: the thinking, the meals and the shopping, with the reasoning shown even on imperfect weeks. Different scopes, both done well.
