Stephen M. Walker II
Product leader, fitness operator, and AI founder. Former Head of Product at Freeletics, now building Fuel.
Led product at Freeletics, now building AI nutrition at Fuel
Stephen is the founder of Fuel and writes most of the Fuel Journal. He builds nutrition coaching for the same audience he has shipped products to for a decade: people who take training seriously and want software that respects it.
From 2017 to 2020 he led product, design, research, content, and subscription monetization as Head of Product & Design at Freeletics, where his teams helped the digital fitness app surpass 50 million users worldwide across 100+ countries, with 70% week-one training activation. That stint — owning every surface that touches habit formation in a fitness app — is the operator lens behind every article here.
After Freeletics he grew Productboard 5x to $50M+ ARR as Senior Director of Product Management (2020–2022), reshaping the product from SMB/PLG-darling to enterprise roadmap software adopted by 6,000+ companies. Since 2022 he has been co-founder and CEO of Klu.ai, an LLM infrastructure platform used by thousands of AI teams — which is why Fuel's AI food logging and coaching feel less hand-wavy than most.
Earlier he ran global UX programs at Amazon (2016–2017) for cross-border eCommerce, led mobile investing design at Capital One (2014–2016), and spent a decade (2003–2014) running Smoov, a boutique design studio shipping work across consoles, desktop, mobile, and web. He speaks regularly at EU CPO Conference, SXSW, La Product Conf, and Product Led Alliance. Verifiable on SMW.ai, LinkedIn, and Speaker Deck.
The Importance of Protein: Why It's the Most Critical Macro for Weight Loss & Muscle Gain
Best Peptide Advice From Huberman Lab, The Drive, FoundMyFitness, & Tim Ferriss (2021–2026)
Food Database Accuracy: Why Your Macro Numbers Drift and How to Audit Them
Sodium Loading for Endurance Racing
A practical, evidence-based guide to sodium loading before long races. Learn when pre-race sodium helps, when it backfires, how it differs from hourly replacement, and how to build a dose that matches heat, sweat rate, and event duration.
Protein Quality Scores Explained: DIAAS vs PDCAAS in Real Meal Planning
A protein log can look solid and still be built on weak feedings. This guide explains DIAAS, PDCAAS, limiting amino acids, and why protein quality matters most when meals are small, calories are tight, or plant protein has to do more work.
Strength Training Minimum Effective Dose During a Cut
The smallest lifting dose that protects muscle in a cut is not a static minimalist program. This guide shows trained men how to keep the muscle-retention signal alive when calories, recovery, and GLP-1 appetite tolerance all get tighter.
Omega-3 Index: What Your Number Means, How Much EPA and DHA You Need, and When to Retest
Most omega-3 advice stays stuck at fish-oil labels. This guide explains what the Omega-3 Index actually measures, what result is worth aiming for, how much EPA and DHA usually moves the number, and why flax or walnuts do not solve the same problem.
Andrew Huberman Supplement List (2026)
Andrew Huberman's supplement list has become internet canon, but his stack keeps changing. This review separates the short list worth copying from the speculative add-ons, the occasional tools, and the compounds that make more sense only with bloodwork and a clear use case.
Everything by Stephen Walker
72 articles in the Fuel Journal, newest first.
