Is Weight Gain Normal During Marathon Training?

Is weight gain normal during marathon training? Yes, weight gain can be normal during marathon training, especially for beginner and age-group endurance athletes. Small increases often reflect training stress, fuel changes, and fluid shifts rather than fat gain. For runners, triathletes, and multi-sport athletes, the scale can move even when training is going well.

If you are wondering, is weight gain normal during marathon training? the short answer is that it often is, particularly early in a training block or when volume increases. What matters more than the number itself is how your body feels and how your training is progressing.

Why This Happens

Increased Muscle Glycogen and Water Storage

When you train more, your muscles store more glycogen, which is the body's preferred fuel for endurance work. Glycogen binds with water, so fuller fuel stores mean more water weight.

This is common when mileage rises or workouts get longer. It shows up most often in the first few weeks of a marathon plan or after adding intensity. The scale goes up even though body composition may not have changed.

Higher Training Stress and Short-Term Inflammation

Long runs, hill work, and new workouts create small amounts of muscle damage. Your body responds by holding extra fluid to support repair and adaptation.

This kind of weight gain is usually temporary. It is more likely during peak training weeks or after hard back-to-back sessions. Many athletes notice it midweek or after a big weekend.

Eating More, Sometimes Without Realizing It

Marathon training increases hunger, but appetite signals can lag behind training load. Some athletes underfuel workouts, then overeat later in the day without noticing.

This pattern is common for beginners and masters athletes who are learning how much fuel they actually need. It does not mean you are doing anything wrong. It means your body is trying to keep up.

Reduced Daily Movement Outside of Training

When training volume goes up, non-training activity often goes down. You might sit more, nap more, or skip casual movement to save energy.

This tradeoff is normal during heavy training. It can slightly shift energy balance even when weekly mileage is high. It tends to show up during busy work weeks or high-stress periods.

Hormonal and Sleep-Related Shifts

Hard training combined with poor sleep can affect how your body manages fluids and hunger. This is especially relevant for masters athletes and multi-sport athletes juggling multiple sessions.

These changes are usually subtle and temporary. They are more likely during peak phases, travel weeks, or when recovery gets squeezed.

Is Weight Gain Normal During Marathon Training for All Athletes?

Weight changes vary by athlete, training history, and life context. Some runners lose weight, some stay the same, and others see small increases. All three can happen during effective marathon preparation.

The key is understanding what the weight change represents. In many cases, it reflects fuel, water, and recovery needs rather than loss of fitness or discipline.

What Matters vs What You Can Ignore

Signs That Matter

• Rapid weight gain paired with worsening fatigue
• Declining workout quality over several weeks
• Persistent soreness that does not improve with recovery days
• Trouble fueling long runs or finishing key sessions

Signs That Are Usually Normal

• Small weight increases during high-volume weeks
• Day-to-day scale fluctuations
• Feeling fuller or heavier after rest days
• Weight changes that stabilize without intervention

This distinction helps you avoid overreacting to normal training responses.

What to Do This Week

Keep Easy Days Truly Easy

If easy runs creep too fast, stress and fatigue rise. Slow your easy pace enough that you could hold a relaxed conversation.

This supports recovery and helps regulate appetite and fluid balance.

Fuel Around Workouts, Not Just After

Aim to eat before long runs and quality sessions, even if the run feels manageable. This reduces rebound hunger later in the day.

Simple carbs before and a balanced meal after are often enough.

Watch Patterns, Not Daily Numbers

If you weigh yourself, do it consistently and sparingly. Compare week to week trends rather than reacting to single days.

Better yet, pair scale data with how your legs feel and how workouts go.

Protect Sleep and Recovery Windows

Extra training only works if recovery keeps pace. Prioritize sleep, especially after long runs and brick workouts for triathletes.

Even small improvements here can stabilize appetite and fluid retention.

Avoid Sudden Training or Diet Changes

Resist the urge to cut calories or add extra workouts to "fix" weight gain. Short-term adjustments often create more stress than benefit.

Stay consistent for now and reassess later.

When to Reassess

Give changes at least two to three weeks before drawing conclusions. Single weeks rarely tell the full story during marathon training.

Reassess if weight continues to rise alongside declining performance or growing fatigue. Patterns matter more than isolated weigh-ins or tough workouts.

If training feels strong and recovery is improving, the scale may simply be reflecting adaptation.

Frequently Asked Questions

Why am I gaining weight even though I am running more?

Running more increases fuel storage and fluid retention, which can raise scale weight. It can also increase hunger and reduce non-training movement. These effects often balance out over time.

Is weight gain normal during marathon training for beginners?

Yes, beginners often see small increases as their bodies adapt to new stress. Early training phases are when glycogen storage and inflammation are most noticeable.

Should I try to lose weight during marathon training?

Most athletes do better focusing on training quality and recovery rather than weight loss. Trying to lose weight during heavy training can interfere with adaptation.

Does weight gain mean I am undertrained or overtrained?

Not by itself. Weight gain is a weak signal on its own. Training performance, fatigue trends, and recovery markers give better information.

Will the weight come off after the race?

Often it does, especially as training volume drops and recovery normalizes. Post-race routines usually bring appetite and fluid balance back toward baseline.

Conclusion

Weight gain during marathon training can feel frustrating, but it is often a normal part of endurance adaptation. Focus on how your training feels, fuel consistently, and give your body time to respond. The scale is only one small piece of the bigger picture.