Should Endurance Athletes Try to Change Body Composition During a Training Cycle?

In Episode 124 of The Eat for Endurance Podcast, I’m joined by sports dietitian and multi-sport athlete Alex Larson, RD LD as we dive into two important topics: triathlon nutrition and body composition for athletes. 

One of the big questions we explore in this episode is whether endurance athletes should try to change their body composition and get leaner during a training cycle. If you’ve been here awhile, you know that I generally encourage athletes not to pursue weight loss or body comp goals while training for an event, since it can increase the risk of low energy availability, injury, and reduced performance. I still believe this to be true for the majority of the clients that I see.

That said, Alex brings a slightly different perspective based on her experience working with clients in her private practice. This is a very nuanced topic, and it was great to unpack the pros, cons, and context with her to better understand how body comp goals might fit into an athlete’s broader fueling and training plan.

Heads up – we talk a lot about body comp for athletes in this episode. While "getting leaner" is a common goal for many active people, I want to be clear: your health, performance, and worth do NOT depend on you being "lean." I didn't explicitly say that in this episode, and I wish I had.

It's okay to want to change your body composition, and for some athletes, this can be done safely in certain situations. It's also okay (and for some athletes, very necessary) to NOT chase body comp goals, ever. So please take care of yourself, and remember - your body is meant to change over time.

Key timestamps in this episode:

8:53: Triathlon nutrition

34:20: Body composition and endurance training

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Triathlon Nutrition for Training and Racing

It’s been a couple of years since I last talked about triathlon nutrition on the podcast, so I was thrilled to bring Alex on to revisit this important topic from different angles.

Triathlon nutrition is tricky because the strategies that work well for running don’t always translate seamlessly to cycling or swimming. As both a sports dietitian and Ironman finisher herself, Alex understands the unique fueling demands of training for three sports at once and has some great tips on nutrition for multi-sport athletes. 

Fueling for Swim, Bike, and Run

While the swim leg is short compared to the others, it sets the tone for the event. You need a solid pre-race meal plus a gel (or two) right before the swim to top off glycogen stores.

The bike is what Alex calls the “mobile buffet,” and is where you can (and should) take in the bulk of their carbs and fluids in long-course races. This is important because you're catching up from not fueling during the swim, and need to prep for a strong run. She encourages all triathletes to use sports drinks in their bottles to ensure they're getting adequate carbs per hour.

By the time you’re out on the run, fueling becomes more logistically difficult and gut tolerance is often challenging, which makes practice, planning, and gut training essential.

Common Triathlete Nutrition Mistakes

Alex and I also discussed some of the most common nutrition mistakes triathletes make, such as underestimating carb needs, forgetting to fuel in the early stages of the bike, or neglecting hydration until it’s too late.

Another pitfall is failing to match everyday nutrition to training demands, which is something Alex emphasized as key for recovery, adaptation, and long-term performance. Harder training days require more carbs and energy overall, while lighter days allow for a bit more flexibility (just make sure you’re not under-fueling).

Nutrition for Ironman Training

For those tackling long-course events, Alex offered many helpful nutrition strategies. This includes building up tolerance to higher carbohydrate intakes, practicing race fueling in training, and learning how to troubleshoot when things don’t go as planned on race day.

Whether you’re preparing for your first sprint triathlon or looking to dial in your fueling for an Ironman, this part of the conversation is packed with real-world, evidence-based advice.

Should You Work on Body Composition During a Training Cycle?

The second half of our conversation shifted gears into a question many endurance athletes wrestle with: should you try to change your body composition during a training cycle?

It’s not surprising that athletes often ask this. After all, there’s a common belief that being leaner will automatically make you faster or more efficient. And while there can be truth to the idea that carrying less body fat may improve running economy or power-to-weight ratio, the reality is much more complicated.

Nutrition, recovery, training quality, and overall health are all intricately connected, so cutting calories or chasing a lower body fat percentage during high-volume training can backfire. That’s why I typically encourage athletes to avoid directly working on weight loss or body comp goals during a training cycle. The risks (low energy availability, injury, hormonal disruption, reduced performance, etc) are often too high.

In my practice and with the types of clients I often see, performance almost always improves when fueling is prioritized over restriction. Sometimes weight and/or body composition changes do occur from the work that we do and the training that is happening, but these are not things we directly try to shift.

In her work, Alex has worked with athletes to pursue body comp goals without compromising their training. She emphasized that this approach isn’t one-size-fits-all, it requires careful vetting (e.g. no history of disordered eating, poor body image etc), and the changes must be VERY slow. The athlete’s health, mindset, and training demands all need to be aligned.

Even then, it’s important to recognize that getting leaner doesn’t guarantee getting faster. It also won't fix your body image issues.

This was such a valuable conversation because it highlighted the gray area that many athletes live in. Yes, body composition can influence performance, but it’s only one piece of the puzzle.

For some athletes, there may be a safe way to address it during training, but for many others, the risks outweigh the rewards. Knowing where you fall on that spectrum is key, and it’s why individualized guidance and working with a sports dietitian near you is important.

Key Takeaways

• Triathlon nutrition requires a sport-specific approach and fueling needs differ across swim, bike, and run

• Nutrition for Ironman training means dialing in carbs, fluids, and recovery strategies for long-course demands

• Body composition goals for athletes are best tackled in the off-season, but with careful planning, some athletes may safely work on them during training with a Sports RD

• Leaner doesn’t always mean faster, as performance depends on many different factors

• A positive relationship with food and a performance-first mindset should guide every nutrition decision

Ready to Fine-Tune Your Fueling?

If you’re struggling with sports nutrition challenges, whether it’s race-day fueling, dialing in your triathlon nutrition, or figuring out how body composition fits into your goals, I can help. I’ve worked with runners, cyclists, triathletes, and other endurance athletes for over 10 years to fine-tune both everyday fueling and race-day strategies. 

Here’s what some of my clients had to say about our time working together:

“Thank you for the guidance you provided me over the last few months of Ironman prep. The information you gave me was so helpful on race day. I stuck to the plan, which led me to feel so good on the run, and finished much faster than I anticipated. You're awesome and I'm so grateful you were on my team :)”

-Sarah B

"I had the pleasure of working with Claire to prepare for my first Ironman. Claire really helped me focus on my daily meal plan during the months of training leading up to the race and then to dial-into my nutrition plan for race day. We experimented with different options during my long training days until we came up with a plan that we thought would work best for me. I kept to the plan on race day and was able to maintain the necessary energy throughout.Thanks to Claire I had a great race and exceeded my expectations."

-Jennifer F.

Here are a few ways to work with me:

• Join my low-cost, low-commitment membership service, Fuel for Life Crew, for $30/month (cancel anytime)

• Check out my free nutrition downloads

• Browse my library of nutrition masterclasses (all are included inside the Fuel for Life Crew membership)

• Fill out a new client inquiry form if you’re interested in 1:1 nutrition coaching (spots limited)

  
  

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Stick them on your water bottle, laptop, or race gear to make fueling fun, no matter where you are!

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Disclaimer: All information provided is for educational and entertainment purposes only and is in no way meant to replace individual medical and nutrition recommendations.