Live Wisely: Why You Might Gain Weight When Starting Half Marathon Training (and Why It’s Totally Normal!)

If you're like me, training for a half marathon is both exciting and a little overwhelming. I just started training for my own half marathon in October, and like many of you, I had a moment of panic when I noticed the scale creeping up during the first few weeks. But guess what? It's totally normal! In fact, it's a part of the process—and here's why.

The 3 Brains in Action: Why Weight Gain Happens (Temporarily)

Training for a half marathon isn’t just a physical challenge; it’s a mental and emotional one too. And it turns out that each of our three brains—the head brain, heart brain, and gut brain—play a role in how our body responds to new training. Let’s break it down:

Head Brain (The Cognitive Brain):

When you start running, your head brain is focused on your goals. You’re tracking your progress, measuring your distance, and thinking about race day. So when you notice a slight increase in weight, your head brain might start questioning, “What’s going on here?” But don’t worry—this is actually quite normal. When you’re increasing your physical activity, your body needs time to adjust. This can include temporary weight gain due to things like water retention and muscle gain. It's not fat, it's just your body getting stronger and more efficient!

Heart Brain (The Emotional Brain):

Your heart brain is all about how you feel. You might be frustrated or even disappointed with the number on the scale, but trust me—this is where you need to give yourself some love and encouragement. You’re doing this for so much more than weight loss. Training for a half marathon is about pushing yourself, building resilience, and achieving something incredible. The emotional payoff—feeling proud, strong, and capable—is just as important as the physical results. So don’t stress about the scale; focus on how amazing you’ll feel crossing that finish line!

Gut Brain (The Instinctive Brain):

Your gut brain is your body’s survival center, and when you start increasing your training intensity, your body reads this as stress. Your gut brain might trigger some water retention as your body holds onto extra fluids, thinking you need them for future runs. This is a normal adaptive response as your body adjusts to the increased physical demands.

Cortisol and the Fight/Flight Response:

Now, here's where things get a bit more interesting. When you start training for something like a half marathon, your body is essentially going through a stress response—even though it’s a good kind of stress. This is because your body views new training as a challenge, and the fight or flight response kicks in to help you adapt and push through.

One of the key hormones produced during stress is cortisol—also known as the "stress hormone." Cortisol plays a significant role in regulating your metabolism, energy levels, and fat storage. When you’re pushing your body to run farther and faster, cortisol is released to provide the necessary energy and focus. However, when cortisol levels remain elevated for a prolonged period (such as in the initial stages of training), it can lead to increased fat storage, especially in the abdominal area.

This is your body’s way of ensuring that you have enough energy reserves for the physical demands of your training. But cortisol’s effects are temporary and, with time, will stabilize as your body adapts to the new demands of training.

The Science Behind the Weight Gain:

• Water Retention: As you run and train, your muscles use glycogen for fuel. For every gram of glycogen stored, your body holds onto about 3 grams of water. This water retention can make it seem like you’re gaining weight, but it’s really just your muscles soaking up what they need to recover.

• Muscle Gain: As you train, your muscles grow stronger and more efficient. Muscle mass weighs more than fat, so your body may gain a bit of muscle, which can show up as a slight increase in weight. But trust me, this is a great thing! Strong muscles are what will help you perform better on race day.

• Inflammation: Training causes tiny tears in your muscles, which is totally normal. As your muscles repair themselves, your body can experience temporary inflammation. This is part of the recovery process and often reflects as weight gain—again, totally normal and temporary.

• Cortisol’s Impact on Fat Storage: Elevated cortisol levels in the beginning stages of training can contribute to temporary weight gain, as your body holds onto fat for energy reserves. But as your training becomes more consistent, cortisol levels will stabilize, and your body will transition from a "fight or flight" mode to a more balanced state of performance.

Personal Story: My Own Journey

When I started training for my half marathon this year, I was excited but also a little anxious. I thought I would see instant results. However, like many of you, I noticed that I gained a couple of pounds in the first few weeks. At first, I was frustrated—I wanted to see the pounds drop, not go up! But then I remembered that this is part of the process. I focused on how I felt during my runs, how strong I was getting, and how much more energy I had throughout the day. Now, I feel more confident than ever that the weight gain is just my body adapting to the new physical demands, and I’m trusting the process.

What You Can Do:

• Trust the Process: The weight gain is usually temporary. Your body is simply adjusting to a new training regimen. Stick with it, and in time, the weight will likely stabilize or drop as your body gets more efficient.

• Focus on How You Feel: Rather than focusing on the scale, pay attention to how you feel during your runs and throughout the day. Are you feeling stronger? More energized? More confident? These are the true signs of progress.

• Be Patient: The early stages of training can bring some ups and downs, but trust me—it’s all part of the journey. The scale will catch up, and you’ll be amazed at how much stronger you feel as you continue to train.

Key Takeaways:

• Gaining weight when you start training is normal and often temporary.

• Your body is adjusting to the new physical demands, which could mean water retention, muscle gain, and inflammation.

• Cortisol is a key hormone involved in the fight/flight response during training, and while it helps you adapt, it can temporarily lead to weight gain.

• Focus on how you feel and the progress you’re making. Training for a half marathon is about building strength and endurance, not just losing weight.

So, if you’re training for a race or starting any new fitness journey, know that it’s okay to see some changes on the scale at first. Your body is becoming stronger, more capable, and ready for what’s ahead. Trust yourself, stay patient, and keep going—you’re doing amazing things!