Coach Nathan Castillo spotting a client at the gym
Meet Your Coach

Nathan
"Nate" Castillo

B.S. Kinesiology from California State University, Fullerton. 8+ years helping men and women — a lot of them over 35 and short on time — build muscle, lose fat, and rebuild their strength. Based in Orange, CA.

My Story

From Injury to
8 Years of Results.

I'm Nathan Castillo — most people call me Nate. I'm a personal trainer based in Orange, California with a Bachelor of Science in Kinesiology from Cal State Fullerton. For the last 8+ years I've helped men and women build muscle, lose fat, gain confidence, and create a body that lasts.

My passion for coaching came from my own journey. Early on, I tore up my shoulder from training the wrong way — I thought more was always better. It took time to learn that real results come from smart programming, proper recovery, and consistency. Not just grinding harder.

That experience shaped everything about how I coach today. A lot of my clients are men and women over 35 with careers and families, and they come to me to get stronger, leaner, and healthier without living in the gym. Evidence-based training, flexible nutrition, and practical coaching that fits into a real life with a real job.

Coach Nate coaching a training session in Orange, CA
"Be Taught. Not Told."

That's the whole philosophy.

I don't hand you a printout and walk away. I teach you why — program design, nutrition, recovery, hydration, sleep, supplementation, the whole picture. The goal isn't dependency on me. It's you knowing exactly what your body needs, long after we stop training together.

Background & Specialty

Real Qualifications.
No Fluff.

B.S. Kinesiology California State University, Fullerton
8+ Years Coaching Hands-on, in-person experience
Specialist Men & women 35+ · busy professionals
On Instagram

Free Game on Instagram.

Nate's most-shared clips — straightforward nutrition tips and training breakdowns, no fluff. The same education his clients get in person, free on your feed. Tap any video to watch on Instagram.

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BUILTBYNATE Instagram post
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Hear It From Clients

In Their Own Words.

★★★★★

"My first meeting with Nate, I shared that I had no confidence, hated my body, and couldn't even look in the mirror. He didn't judge me — he encouraged me on how we could change me, not just physically but mentally. After 3 months I lost 30 pounds, 8% body fat, and gained 6 pounds of muscle. I pose in the mirror now instead of avoiding it, and I feel strong. It was the best decision I made for myself."

— Brandon M. · Yelp
★★★★★

"I came to Nate having retired from collegiate cross country — experiencing pain when running and barely any strength on me. He made sure to focus on the quality of every rep. Today, I'm feeling stronger than ever and running pain-free. I've built several pounds of muscle while lowering my body fat. Coach Nate will push you to be a better version of yourself."

— Rachel K. · Yelp
★★★★★

"In my consultation I opened up and told Nate my health status, and he had a program in place — not only physical and healthy, but mental. Since then, I'm the healthiest and happiest I've been in my entire life. He's not just a fitness coach; he encourages me every day. It's only been a year — I can't wait for year #2."

— Arlene P. · Yelp
Think We'd Be A Fit?

Your First Session
Is On Me.

Not a sales call — an actual training session, plus an InBody scan and a walkthrough of your plan. Men and women, any starting point. No pitch, no pressure, no card.

Claim My Free Session
Text Nate