Fat and Endurance Performance: Why Athletes Need to Burn Fat Efficiently

Is fat an athlete’s enemy?

If you are trying to improve your power-to-weight ratio, excess body fat is weight you may want to lose. But there is an interesting contradiction in endurance sports: while reducing excess body fat can improve performance, your ability to use fat as a fuel source during exercise is critically important for long-distance cycling, running, triathlon, and other endurance events.

For endurance athletes, the goal isn't simply to burn more calories. It is to become more aerobically efficient, allowing your body to use fat for energy while conserving its limited carbohydrate stores.

Why Fat Is Important for Endurance Athletes

The human body stores energy in several forms, but fat represents an enormous energy reserve. Even a relatively lean athlete carries enough stored fat to provide energy for many hours of exercise.

The challenge is that the body cannot access all of that stored energy at the same rate or intensity.

During lower-intensity aerobic exercise, fat can provide a significant portion of the energy required by working muscles. As exercise intensity increases, the body increasingly relies on carbohydrates because they can provide energy more rapidly.

This is one reason fat oxidation is so important to endurance athletes.

The ability to access and utilize fat efficiently can help preserve glycogen and carbohydrate stores during prolonged exercise.

What Is Fatmax?

Fatmax refers to the exercise intensity at which your body is oxidizing fat at its highest rate.

For endurance athletes, training at appropriate intensities can improve the body's ability to utilize fat as a fuel source. This is particularly relevant for events lasting two hours or more, where conserving carbohydrate stores can become a major factor in performance.

Training and racing substantially above your individual Fatmax intensity generally increases your reliance on carbohydrates. As intensity rises, fat oxidation typically decreases while carbohydrate utilization increases.

The exact Fatmax intensity varies considerably from athlete to athlete. It is influenced by fitness, training history, nutrition, genetics, exercise intensity, and other factors.

Why Carbohydrate Becomes So Important at Higher Intensities

Although the body stores considerably more energy as fat than as carbohydrate, carbohydrate has an important advantage: it can provide energy at higher exercise intensities.

Fast-twitch muscle fibers also tend to rely more heavily on carbohydrate than slow-twitch fibers. Sustained high-intensity efforts, climbing at race pace, attacks, sprints, and other maximal efforts can therefore consume glycogen much more rapidly.

This creates an important endurance-sport balancing act.

You want your body to be capable of using fat efficiently at aerobic intensities while maintaining enough carbohydrate availability to support the harder efforts.

The Problem With Relying Entirely on Carbohydrate

An endurance athlete can consume carbohydrates during exercise, but there are practical limits to how much carbohydrate can be absorbed and tolerated while exercising.

As exercise intensity increases, feeding can become more difficult. Blood flow is directed toward the working muscles and away from the digestive system, and gastrointestinal distress can become more likely.

This is one reason endurance athletes cannot simply continue replacing every calorie they burn during a long event.

Instead, successful endurance performance involves a combination of stored energy, carbohydrate intake, fat oxidation, pacing, and training adaptations.

The more effectively an athlete can use fat aerobically, the more valuable their limited carbohydrate stores can become.

Does Having More Body Fat Make You a Better Endurance Athlete?

Not necessarily.

This is where the distinction between body fat and fat oxidation becomes important.

Having additional body fat does provide additional stored energy, but excess body fat does not directly make you faster. In cycling, additional body mass can be particularly costly when climbing, and excess body fat can also increase aerodynamic drag and make thermoregulation more difficult.

In other words, you don't need to carry extra body fat simply because fat is an important endurance fuel.

Your body already has a substantial supply of stored fat.

The goal for an endurance athlete is to become efficient at accessing and using that stored energy, not to maintain unnecessary body fat.

Fat Burning and Your Power-to-Weight Ratio

For cyclists, body composition can have a significant impact on performance, particularly when climbing.

Power-to-weight ratio is commonly expressed as watts per kilogram. If an athlete can maintain the same power while reducing unnecessary body mass, their power-to-weight ratio improves.

However, weight loss should not come at the expense of training quality.

A cyclist who loses weight but cannot train effectively, recover properly, or produce the same power may ultimately become a slower cyclist rather than a faster one.

This is why the timing and rate of weight loss matter.

When Is the Best Time for an Athlete to Lose Body Fat?

Reducing body fat requires a caloric deficit, meaning you consume fewer calories than your body uses over time.

The problem is that maintaining a caloric deficit can interfere with training and recovery. If you consistently underfuel your training, you may experience reduced performance, poor recovery, increased fatigue, and difficulty maintaining training intensity.

For many endurance athletes, the best opportunity to gradually reduce excess body fat is during the off-season or base-training period, when racing is less frequent and training intensity may be lower.

Unfortunately, this is also the time of year when many athletes gain weight.

A better strategy is to plan body-composition changes rather than attempting a rapid weight-loss program immediately before an important race.

Slow and Steady Weight Loss Is Better for Performance

Rapid weight loss may look attractive on the scale, but endurance athletes should be cautious about aggressive calorie restriction.

A gradual reduction in body fat allows you to maintain a greater portion of your training quality while continuing to provide your body with the nutrients it needs for recovery.

The objective should be to arrive at the racing season lean, well-trained, well-fueled, and healthy—not simply lighter.

The Bottom Line: Burn Fat, But Don't Chase Fat

Fat isn't simply the enemy of an endurance athlete.

Excess body fat may hurt your power-to-weight ratio, but the ability to burn fat efficiently can help improve endurance performance.

Long-duration endurance events are partly about conserving energy as much as they are about producing it. An athlete who can efficiently utilize fat at appropriate aerobic intensities can potentially preserve valuable carbohydrate stores for later in the event, when higher intensities demand them.

The key is understanding the difference between having body fat and being metabolically efficient at using fat for fuel.

For endurance athletes, the goal isn't to carry more fat. It is to become better at using the fat you already have while preserving carbohydrate for when you need it most.

References

Peak Performance Cycling, Issue 224, pp. 1–4.