If you’re struggling with the transition to a ketogenic diet, chances are you’re not eating enough fat. This is one of the top reasons athletes fail to stay on track long enough to become fully fat-adapted.

Basic Reasoning

Let’s start with the fundamentals. Being ketogenic means that your body becomes efficient at:

• Using fat for fuel
• Breaking down body fat
• Producing ketones
• Utilizing ketones effectively

For now, we’re going to focus on using fat and breaking down body fat.

If you have a lot of body fat, you don’t need as much dietary fat. This is where most people on a properly structured ketogenic diet see major benefits. When fat intake is adequate but not excessive, body fat loss happens more readily.

However, many people fall into the trap of the “butter chugger” philosophy, where they consume excessive fat and then wonder why they aren’t losing weight. Your body won’t release stored fat if it has no reason to.

A Real-World Example

A perfect example of how little fat intake is needed when body fat stores are high comes from the case of Angus Barbieri, who fasted for 382 days. During that time, he survived on vitamin and yeast-based protein supplements without any significant health issues.

👉 Study: Features of a Successful Therapeutic Fast of 382 Days’ Duration — PMC

Now, to be clear, I’m not suggesting anyone fast for a year. The point is simple: if you have a lot of body fat, your need for dietary fat is lower. Conversely, if you have low body fat, your dietary fat intake must increase to compensate.

How Athletes Are Different

Athletes operate in a completely different metabolic context than the average person. Here’s why:

1. Athletes tend to be leaner — Fat loss is often not their primary goal.
2. Athletes train at a higher intensity and frequency — They place extreme energy demands on their bodies.
3. Athletes have more lean mass — This means higher fuel demands, particularly for recovery.

These three factors create a higher overall fat requirement, making adequate dietary fat intake a top priority for any athlete looking to transition successfully into a ketogenic lifestyle.

Leanness: The Missing Energy Source

One of the biggest mistakes lean athletes make is undereating fat when switching to keto. Many endurance athletes, weightlifters, and CrossFitters are accustomed to eating high-carb, low-fat diets. The constant intake of carbs means body fat is less preferentially used as a primary fuel source.

When they remove the carbs but don’t compensate with enough dietary fat, they often feel sluggish, weak, and unable to perform at their usual level. This leads to the false assumption that keto doesn’t work for athletes when, in reality, they’re just under-fueling.

Activity: Energy Demands Beyond Daily Living

A standard ketogenic diet designed for body fat loss often limits dietary fat intake to create a fuel macro deficit. An athlete’s body operates under entirely different rules. Training at high intensities increases energy expenditure significantly, which means that:

• Fat intake must be sufficient to fuel performance and recovery.
• Glycogen stores will still be used but are replenished efficiently through gluconeogenesis and the breakdown of triglycerides…. If they are available.

Failing to meet fuel macro demands results in poor recovery, performance drops, and fatigue.

Lean Mass: More Muscle, More Fuel Needed

Muscle is an expensive tissue to maintain. More lean mass means a higher resting energy demand, meaning ketogenic athletes require more total fat intake.

For the average person, 1 gram of fat per pound of lean body mass or body weight is usually sufficient for maintenance and energy balance. However, athletes — especially those engaged in high-intensity or endurance training — often need 1.25 to 1.5 grams of fat (or more) per pound of lean mass or body weight to sustain energy levels, optimize performance, and support recovery.

For example:

• A 150-pound non-athlete with moderate activity levels may do well on 150g of fat per day.
• A 150-pound athlete training at a high intensity may require 188–225g of fat per day to meet energy needs.

This higher fat intake ensures that athletes don’t under-fuel, which can lead to performance loss, excessive fatigue, and impaired recovery.

Practical Takeaways for Ketogenic Athletes

• If you’re lean, eat more fat. You don’t have the stored reserves to make up for a fuel deficit.
• If you feel sluggish, check your fat intake. Under-eating fat is a common reason for poor performance during keto-adaptation.
• If your training volume is high, adjust accordingly. You should experiment with your fat intake to optimize energy levels.
• Don’t be afraid of protein. Fat is essential, but adequate protein intake is also critical for recovery and muscle retention.

Final Thoughts

Adapting to a ketogenic diet as an athlete requires a different strategy than someone who is sedentary or looking to lose body fat. Fat intake is a crucial part of making the transition smooth and effective. The key is knowing your energy needs, adjusting accordingly, and trusting the adaptation process.

If you’ve struggled with performance or energy on keto, it’s time to take a hard look at whether you’re truly fueling yourself enough — and if you’re an athlete, that likely means eating more fat.