How keto affects body composition, strength, and performance.

In 2017, Rachel Gregory published one of the first controlled studies looking at a ketogenic diet in recreational CrossFit athletes. Not sedentary subjects. Not lab-bound theory. People training under load.

That matters. Because most nutrition conversations still revolve around the wrong question: Is keto good or bad?

That’s lazy thinking. The real question, the one that actually applies to strength athletes, is: When does keto improve body composition, and when does it limit performance?

What Gregory’s Study Actually Showed

Gregory’s research, published in the Journal of the International Society of Sports Nutrition (2017), examined CrossFit-trained individuals over six weeks. One group followed a ketogenic diet, the other consumed a traditional mixed macronutrient diet.

They measured:

• Body composition
• Strength performance
• Aerobic capacity

The results weren’t extreme—but they were telling.

• The ketogenic group lost body fat.
• Strength was maintained.
• Aerobic capacity remained largely unchanged.

At first glance, that sounds like a win. But if you’re paying attention, you’ll notice what’s missing: No meaningful increase in lean mass. No jump in performance.

Leaner Isn’t Always Better

Keto works for fat loss. That’s not controversial.

Reduce carbohydrates → lower insulin → appetite drops → caloric intake falls → body fat decreases.

But here’s the trade-off:

• Less available glycogen
• Reduced capacity for repeated high-intensity efforts
• Limited environment for muscle growth

So while the scale moves and body fat drops, you’re not necessarily becoming a more capable athlete. And that’s the disconnect. Most people chase aesthetics rather than output.

Why Fuel Source Matters

High-intensity training—whether it’s heavy barbell work, sprint intervals, or repeated CrossFit efforts—relies heavily on glycogen.

When carbohydrates are chronically restricted:

• Glycogen stores decline
• Training intensity can suffer
• Recovery becomes less efficient

You can still train hard… for a while. But you’re not building the same engine.

This is where keto stops being a performance strategy and starts becoming a limitation—if used at the wrong time.

Keto Is a Tool—Not a Lifestyle

Here’s where most people get it wrong. They find something that works… and refuse to move on from it.

Keto, and more broadly anabolic-style low-carb dieting, has a place in a performance program when:

• You need to drop body fat quickly
• You’re managing a weight class
• You’re improving diet discipline and control
• You’re in a short-term cutting phase

In these cases low-carb becomes a strategic advantage. But avoid living there when:

• You’re trying to build muscle
• You’re pushing high training volume
• You need repeated high-output efforts
• You’re preparing for competition

Because you don’t build peak performance in a restricted fuel environment.

The Real Skill: Metabolic Flexibility

Rachel Gregory has since emphasized the concept of metabolic flexibility—and this is where things actually get useful.

But let’s strip the buzzword down: Metabolic flexibility is the ability to use the right fuel for the job.

Not “I don’t eat carbs”, “I’m always in ketosis”. That’s not flexibility—that’s dogma.

A smarter approach looks like:

• Low-carb when leaning out
• Higher-carb when training demands increase
• Adjusting intake based on output

Fuel should match function. Always.

Especially For Women: Stop Living in the Deficit

This is where things get sideways fast. A lot of women fall into the trap of:

• Chronic low-carb dieting
• High training frequency
• Under-fueling
• Plateaued results

They’re lean… but not progressing. Being under-fueled isn’t discipline—it’s a ceiling.

If the goal is:

• Strength
• Muscle
• Longevity

Then nutrition has to support performance—not just aesthetics.

Final Takeaway

Rachel Gregory’s study didn’t prove keto is superior. It showed something far more valuable:

You can use keto to improve body composition without destroying performance—but it’s not where peak performance is built.

And that’s the nuance most people miss. Keto isn’t wrong. Carbs aren’t the enemy. They’re tools.

The real question is whether you know when to use them.

If you’ve been spinning your wheels running low-carb year round, it might be time to shift gears. Check out our Anabolic Protocol. It’s not about abandoning keto, it’s about using it with intent. If you want to get lean without sacrificing muscle or output, this is how you do it.

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Pod: Ep 543 – An Intelligent Approach to Keto with Rachel Gregory

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Blog: Mastering the Power Athlete Anabolic Diet