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How to Trim Weight While Still Crushing Endurance Training

by Dr. Alex Harrison | Dec 31, 2020

Entire libraries have been written on the topic of weight loss—entire industries, companies, and academic fields are dedicated to people losing weight. And many of the same principles found in the bounty of available books and media on the topic apply to endurance athletes. So, why write an article on trimming weight while nailing training and health?

Because despite all the resources out there, literally thousands of books written about weight loss for the lay-person, there is very little good information available for endurance athletes who would like to trim their weight, but still crush lofty training goals.  

Dozens of diet books and programs exist, but very few combine proper fueling for grueling triathlon training with sustainable fat loss. The RP Diet for Endurance is one book that does just that. (Yes, it’s co-written by me.)

First and foremost for an endurance athlete, before you jump into a plan to lose weight, there are some factors to consider wisely—like is it worth the trade-offs, can you sleep more during this time to make up for the recovery, do you have any of the signs that now is not the time to trim weight, such as chronic fatigue, cold, or hunger or a history of disordered eating?

RELATED: Is Trimming Weight for Performance Worth the Trade-Offs?

Once you consider these factors, then you should know the things that high-performance endurance athletes do when they want to sustainably lose weight:

  1. They set a strict timeline for fat loss and have a plan for future weight maintenance.
  2. They target a conservative weight loss rate.
  3. Fuel their training like they’re not trying to lose weight.
  4. Know how much of each macronutrient to eat.
  5. Choose high-volume foods when hunger is present.
  6. Eat protein around the clock.
  7. Keep fats reserved for outside training and use them strategically.
  8. Create a calorie deficit by limiting fats to almost exclusively healthy fats.
  9. Eat loads of veggies.
  10. Sleep slightly more than normal, and actively manage their stress.
  11. Reduce calories temporarily and methodically.

Let’s break each one down:

Why should my weight loss be timeline-constrained?

If you’re not setting a discrete timeline for your weight loss efforts, you’re setting yourself up for burnout. A healthy diet should be a lifestyle; weight loss diets should not. Incorporating all your training and life stressors into a future plan for weight maintenance once your weight loss phase is over is more important than the weight loss itself.  

Minor body weight fluctuations of 2-4% are common with food consumption variability, hydration differences, and hormone cycles. But if your ups and downs on the scale haven’t been of that normal amount, then you’d be wise to consider what weight maintenance takes as a lifestyle for you as an athlete, before pursuing weight loss.

Keeping weight loss phases succinct serves three primary purposes:

  1. It prevents long-term diet fatigue and the hormonal trouble and subtle but chronically slower metabolism that might result.
  2. It provides psychological fortitude to do something potentially rigorous by providing a short time frame with light at the end of the tunnel. That light at the end of the tunnel is a marked increase in calorie consumption that should ensue during the subsequent intentional move into a weight maintenance approach.
  3. It allows you to be selective with your training and life stressors, and ensure that they are compatible with your current choice to attempt weight loss. If you’re not totally sure that your life stressors are currently compatible, then re-check those factors you should first consider in ‘Is Trimming Weight for Performance Worth the Trade-Offs?’

How fast should I lose weight?

At the absolute maximum, 1% of body weight lost per week is OK for folks who are farther from their ultimate weight loss goal.

For most triathletes, 0.5-0.8% of body weight lost per week is better for performance.

Cutting calories too low and losing weight too quickly might feel sustainable initially, but it invariably leads to poorer health and performance, and weight regain. You’re not going to be the exception to this rule.  

Why should I fuel training like I’m not trying to lose weight? 

What does fueling training mean? It means consuming enough energy before, during, and after training such that your performance ability and training adaptations are perfectly maintained.  

Consuming a large mixed meal 2 to 2.5 hours before training will set you up best—high in carbohydrate, with moderate amounts of protein and some limited healthy fats. If crunched for time, you might even be able to skip it by consuming a blend of whey protein and your workout carb source about 20 minutes before you jump in the pool or on the bike or treadmill.

Fueling training also means consuming at least the minimum amounts of intra-workout carbohydrates, and not doing fasted training.  

Sure, you can do fasted training, but the evidence is clear that your power and speed will be better, and your heart rates lower for a given output, if you fuel during training. Even for training sessions as short as 45 minutes!  

Most triathletes can lose weight and perform best while using the recommended rates of intra-workout carbohydrate consumption found in this table: intra-workout carb needs per hour of training. (For more tables like this one, The RP Diet for Endurance is the place to go.)

Not sure how to consume that much carbohydrate during training? Check out this article: 'When and How to Use High-Carb Fueling'

How much protein should I eat for weight loss?

The answer to how much protein you should eat boils down to how much lean body mass you have, and how much you’d like to keep it. 

If you’re a very well-muscled recovering gym-addict, like me, or you’re a very lean, high-performing endurance athlete, then you can err on the lower side of 0.6-0.8 grams of protein per pound of lean mass.

If you’d like to retain all your hard-earned muscle for all the benefits it provides you in performance, personal aesthetic preference, health and longevity, then erring a little higher, up into the 0.8-1 grams of protein per pound of lean body mass is a better option. This is the range of protein consumption that everyone should start with when starting out seeking fat loss.

For example, for a 160-pound female triathlete that might look like consuming 95-120 grams of protein daily. For a 200-pound male triathlete, that might be about 120-160 grams. Lean body mass differences are the only differences in consideration here.

Protein is important around-the-clock! You worked hard for your muscle. Keep it! Steady consumption of high-protein foods is the best way to accomplish that goal, and helps keep blood sugar steady when you need it to be.

How much fat should I eat for weight loss?

Dietary fat is necessary for optimal hormone function and production. If you go below basic minimums, even for a short time, the results are typically: 

  1. Increased hunger
  2. Stronger cravings
  3. Poorer performance and energy

The good news is, so long as you stay above about 0.3 grams of fat per pound of body weight, any hormone or performance issues aren’t likely to be directly linked to insufficient fat consumption. We can use this to our advantage as endurance athletes because dietary fats are quite high-calorie and don’t directly provide much, if any, energy for training. Our bodies have ample resources for burning fats and accessing those fats during training.  

Generally, 0.6 grams of fat per pound of body weight is the maximum needed, especially during a weight loss diet phase.

If you’re interested in a higher fat diet approach as an endurance athlete, check out: 'Can Fat Adaptation Make You Faster?'

How much carbohydrate should I eat for weight loss?

This answer boils down to: “How much are you burning?” During a weight loss phase, starting with a minimum of 1 gram per pound of body weight for a rest day is a good bet. Some folks will be able to get eat up to 2 grams per pound of body weight for rest days and still see substantial weight loss.

But what about training days? That’s when you add up all the carbs burned during training!

Here are some good rules of thumb to follow for minimum carbohydrate needs, daily:

Running: Distance (km) x Body Mass (kg) x 0.25

Cycling: Distance (km) x Body mass (kg) x 0.1

Swimming: Distance (km) x Body mass (kg) x .75

If you do multiple training sessions in a single day, add up all your sessions worth of carb-burn and consume that as a minimum for the day. If your training is under 90 minutes for the day, then that might not add up to very much, so adding these amounts to your rest day minimum is a good idea.

Confused? We’ve built a calculator that does all the math for you: RP Endurance Macro Calculator.

Why high-volume foods?

High-volume foods are foods that physically take up more space in your digestive system. They’re also usually more nutrient dense and have a higher fiber content, both of which are good for your health.   

The only time not to choose high-volume foods might be during training, when the gut is more sensitive to fiber and food volume. Otherwise, eat your heart out on mostly whole and limited-processed foods, and your hunger will be much better managed than if you were to choose highly processed foods outside of training.

How can I use dietary fat to my advantage?

Fat consumption slows down the absorption of everything it’s consumed with. This is a good thing! (Except when you’re training.)

Increasing a meal’s fat content can be used strategically to:  

  1. Prevent blood sugar spikes to prevent energy crashes.
  2. Smooth out absorption of carbs for upcoming workouts.
  3. Manage hunger by consuming fat with a meal that might be followed by a longer delay before the next meal.

How to create a calorie deficit while eating healthy fats

Saturated fats sure are tasty! Cake, sweet dairy treats, donuts, cookies, pies, marbled or processed meats can all be delicious and seem even more appetizing when you’re trying to trim weight.  

You’ll be wise to avoid or limit them, however, if you’re trying to trim weight, because they’re packed with calories and are not usually very nutrient dense. Limiting your healthy fat consumption to things like almonds, avocados, and olive or canola oil is a good idea if you’re going to try to keep your fat consumption to the levels more optimal for weight loss as a triathlete.

How important are veggies, really?

Could you lose weight without them. Sure. Should you? Nope! And your weight loss efforts will be much easier if you include copious amounts of vegetables. Veggies are not only nutritious and fiber-rich, but they’re incredibly high-volume and filling. Getting a good chunk of your daily carb needs from vegetables is one of the most time-tested strategies for creating a calorie deficit and sustaining good satiety—both of which you’ll need if you plan to maintain your weight after the weight loss phase has passed.

Why are sleep and stress management important for weight loss?

Neither of these seem important towards your weight loss efforts, until they become really important. These are the two biggest things that derail the weight loss efforts of the hardest working folks.

Moreover, when in a calorie deficit, sleep needs are increased because energy availability is lower. This is particularly true in order to recover well from workouts and maintain your training efforts. Sleep more!

Intentionally manage your stress by choosing a time to lose weight when you may be able to pare back other commitments in your life. Stress is cumulative—ie. training stress plus life stress plus weight loss stress equals too much stress. Intentionally choosing the timing of a weight loss diet that works for you and your life is as valuable all the other components of your effort.

For athletes, this also means: Don’t attempt to trim weight in your lead-up to races or in the highest volume phases of your training.

Will I need to reduce calories at some point?

Yes, metabolic adaptation is a real thing. Your metabolism does slow down when you eat less. For most non-chronic dieters, it’s minimal and very much reversible. This is not true if you’re chronically on a weight loss diet or yo-yo-ing your weight loss efforts. That’s why constraining your weight trimming effort to a shorter time-defined phase, keeping it mild, and continuing to train and to fuel training as if you weren’t in a calorie deficit at all is key to minimizing these effects.  

Because of this slight metabolic adaptation, there may come a time when you need to reduce your calories. Be patient with yourself before doing so and ensure that your weight loss rate stays in the 0.5-0.8% of body weight per week, and you’ll be much more likely to continue performance improvements and maintain your weight loss permanently.

Parting words of encouragement

Weight loss can be hard. Sometimes it’s worth it; sometimes it’s definitely not. Choose when and if to take on a weight loss phase wisely. If the time is now, be gentle and patient with yourself throughout the process. Plan intelligently and use strategies known to be common among other successful folks. Use science to your advantage. Then, enjoy the fruits of your labor with what really matters: a healthy lifestyle and a loving long-term relationship with your body, your food, your sport, and your weight.


Dr. Alex Harrison, a certified USA Triathlon coach, holds a PhD in Sport Physiology and Performance. He is the author of The RP Diet for Endurance, creator of the RP Endurance Macro Calculator, and has authored and contributed to dozens of articles. When he isn’t pumping out training and nutrition plans in his RV-garage-turned-mobile-office, he can be found on his bike, clinging for dear life to his wife’s wheel.