Home
Articles
Nutrition
Why Keto Diets Might Cost You Muscle Mass

Why Keto Diets Might Cost You Muscle Mass

Science confirms: Keto diets can lead to significant muscle loss, especially for lifters.

Written By Jim Stoppani, PhD

Updated January 8, 2025

Keto diets have been hyped for years as the ultimate weight-loss hack, but when it comes to building and preserving muscle, the science tells a different story.

A recent review study published in the British Journal of Nutrition revealed that keto diets may actually cause more muscle loss than other diet strategies—especially for those who lift weights .

Let’s break down why this happens and what a smarter fat loss strategy looks like.

What Exactly Is A Keto Diet?

A ketogenic diet is a high-fat, moderate-protein, extremely low-carb approach—typically limiting carb intake to less than 50 grams per day.

The goal is to push your body into a state of ketosis, where it burns fat for fuel instead of carbohydrates. At first glance, it sounds great: rapid fat loss, a metabolic shift, and a simplified diet plan. But here’s the catch—most of the initial weight loss is water weight, not actual fat.

And long-term results? The research shows keto doesn’t outperform other diet strategies for fat loss over extended periods (six months or more).

The Big Problem with Keto Diets

Every calorie-restricted diet eventually hits a plateau—that point where weight loss slows or stalls.

When this happens, the next logical step is to reduce calories further. But on a keto diet, where do those cuts come from? With carbs already stripped down to almost nothing, your only options are protein or fat—and cutting either isn’t ideal, especially if your goal is to build or maintain muscle.

Instead of diving straight into keto, a smarter approach is to gradually reduce carbs in smaller steps, around 50 grams at a time, each time progress stalls—as I prescribe in Dieting 101 . This gives you room to adjust your diet progressively rather than slamming into a metabolic wall.

Muscle Loss on Keto: What the Research Says

The review study found that despite keto diets being higher in protein, subjects on a keto diet lost significantly more muscle mass than those on other diet plans.

In one study, participants following a keto diet for 12 weeks lost 8 pounds of lean mass, compared to just 2 pounds of lean mass lost by those on a low-fat diet.

Why does this happen? Researchers believe the culprit lies in muscle protein synthesis (MPS)—the process your body uses to build and repair muscle tissue. Keto diets appear to disrupt this process, likely due to biochemical changes in metabolic pathways caused by low carb intake.

In simpler terms: Carbs are essential for supporting muscle growth and maintenance, even during fat loss.

A Smarter Approach to Fat Loss

If building and maintaining muscle is a priority, keto probably isn’t your best bet.

Here’s what to do instead:

Keep carbs in your diet. Reduce them gradually as needed, rather than cutting them drastically from the start.
Focus on protein intake. Keep your protein high to support muscle protein synthesis. You should be consuming at least 1 gram of protein per pound of bodyweight per day, and even up to 1.5 grams.
Strength train consistently. Lifting weights will help preserve muscle mass during fat loss.

For a detailed breakdown of how to structure your diet for maximum fat loss and muscle retention, check out my free Dieting 101 guide. It’s a smarter, science-backed approach to getting lean while holding onto your hard-earned muscle.

My Takeaway On Keto

Keto might work for short-term weight loss, but it’s not the best option if your goal is to build and maintain muscle mass.

Carbs play an essential role in supporting your muscles, and the research makes that clear.

Skip the extreme cuts, be strategic with your diet, and stay consistent in the gym. Your muscles will thank you!

FAQ: Keto Diets and Muscle Loss

1. Why do keto diets cause more muscle loss compared to other diets?

Keto diets are extremely low in carbohydrates, which can disrupt muscle protein synthesis (MPS)—the process responsible for repairing and building muscle. Research suggests that this disruption happens due to biochemical changes in metabolic pathways caused by low-carb intake, making it harder for your body to maintain lean muscle mass.

2. Can I still build muscle on a keto diet if I lift weights?

While it’s possible to build muscle on a keto diet, it’s not optimal. The recent study highlighted in this article found that individuals on keto diets lost significantly more lean muscle mass than those on a low-fat diet, even with consistent weight training.

3. Isn’t rapid weight loss on a keto diet a good thing?

Much of the initial weight loss on a keto diet is water weight, not fat. Over time, keto doesn’t show superior fat-loss results compared to other diets, and the extreme carb restriction can make it harder to sustain progress or adjust when weight loss plateaus.

4. What’s a smarter approach than a keto diet for fat loss?

Instead of slashing carbs all at once, try gradually reducing your carb intake by about 50 grams at a time whenever you hit a weight loss plateau. This approach keeps your metabolism stable, supports muscle protein synthesis, and provides flexibility for continued fat loss.

5. Are carbs essential for muscle growth and maintenance?

Yes, carbohydrates play a critical role in muscle protein synthesis, workout performance, and recovery. Cutting carbs too drastically can reduce your ability to build and maintain muscle, even with adequate protein intake and resistance training.