YC Spring 2026 (P26) founder

Manuel Castro

Founder of Napkin Math, AI nutrition coach in your pocket

Napkin Mathconsumer17 public signals

Company

Manuel Castro is listed as a founder of Napkin Math. Napkin Math is the personalized AI food journal that people love to use. We gamify nutrition tracking so people are 2x more likely to stick with us than other trackers. Claire, Manuel, and I (best friends for 10 years from MIT) are obsessed with how we can make nutrition fun, and turn fun into health outcomes. === Existing consumer health apps focus on scaling a one-size-fits-all solution: calorie deficits. But they don’t answer the questions you actually have. Food is deeply personal, and so is Napkin Math: Get the fuel you need for marathon training, while understanding you eat catered office lunches five days a week. Discover what’s triggering your stomach irritation, without sacrificing your weekly dinner with friends. Napkin Math tailors a plan for not only your specific health goal, but also your life.

Founder traction evidence

Public posts and activity attributed directly to this founder.

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    Im thrilled to launch @NapkinMath on @ProductHunt today with @clairen19 and @jynnie ! Napkin Math is the hyper-personalized AI food journal that helps people achieve their health goals as simple as taking a photo of your food so cute you'll share it with a friend Check us out! 0:00 / 0:05

    Im thrilled to launch @NapkinMath on @ProductHunt today with @clairen19 and @jynnie ! Napkin Math is the hyper-personalized AI food journal that helps people achieve their health goals as simple as taking a photo of your food so cute you'll share it with a friend Check us out!...

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    We're building Napkin Math for how real people eat and live. Join us! Quote Y Combinator @ycombinator · May 27 What’s messing up your tummy? Napkin Math ( https:// napkinmath.club) knows. Napkin Math is the hyper-personalized AI food journal that helps people achieve their health goals. Congrats on the launch, @jynniit, @clairen19 & @manny4c! https:// ycombinator.com/launches/QXK-n apkin-math-hyper-personalized-ai-food-journal …

    We're building Napkin Math for how real people eat and live. Join us! Quote Y Combinator @ycombinator · May 27 What’s messing up your tummy? Napkin Math ( https:// napkinmath.club) knows. Napkin Math is the hyper-personalized AI food journal that helps people achieve their...

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    Now we just had an explosion heard from Potrero Hill. Sounded like it came from mission direction.

    Now we just had an explosion heard from Potrero Hill. Sounded like it came from mission direction.

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    I love this! People should absolutely do this and the hardest part is tracking your food. The rest was automated or a test. That’s why we are making Napkin Math, so you have the data to unlock your health. Quote Amy Deng @amydeng_ · Jun 16 I’m an AI researcher turned brain tumor patient, and recently I used the models to crack my mystery fatigue faster than my PCP could. I believe everyone can do the same with their own symptoms. Here’s how:

    I love this! People should absolutely do this and the hardest part is tracking your food. The rest was automated or a test. That’s why we are making Napkin Math, so you have the data to unlock your health. Quote Amy Deng @amydeng_ · Jun 16 I’m an AI researcher turned brain...

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    Wow! @ProductHunt really delivered on signups! Now we just gotta see if they retain as well as our usual cohort

    Wow! @ProductHunt really delivered on signups! Now we just gotta see if they retain as well as our usual cohort

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    If an agent knew everything you ate what would you have it do?

    If an agent knew everything you ate what would you have it do?

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    Fable are you there??

    Fable are you there??

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    Hell ya! New calendar preview thanks to Fable 5 0:06 / 0:10

    Hell ya! New calendar preview thanks to Fable 5 0:06 / 0:10