Can You Lose Weight While Training For An Ironman? Nutritionist Answers
Training for an Ironman while trying to lose weight feels impossible for many triathletes. In this article, I'll show you why this happens and give you a practical framework to make it work without compromising your training.
Many think Ironman training will automatically lead to weight loss.
But what happens is that triathletes often aren’t able to do this at all, and occasionally, the exact opposite happens. The very thing they think will help them lose weight – all that training – actually makes it harder.
I’ve seen this with the triathletes I’ve worked with in a 1:1 capacity. Some triathletes successfully lose weight while still fuelling their training, but in total candour, I’ve had some who weren’t able to, and so instead, we focused on fuelling their Ironman training properly and got back to it after their race.
This is because it is important to understand what is actually happening in your body when you combine Ironman training with weight loss attempts.
You're already putting your body under enormous stress when training for an Ironman. We're talking about 10-15 hours of training per week minimum for most triathletes.
Your body is constantly trying to adapt to long runs, four-hour bike rides or more, and swim and strength sessions.
This is a heck of a lot of physiological stress on the body, and then you decide to add a calorie deficit on top of this because that’s what’s required for true weight loss, or more specifically, fat loss, which is the real goal.
But here's where things get interesting.
Your body doesn't really know that you’re trying to get faster or that you’re trying to lose weight for your race. It only knows two things: you're doing a lot of physical work and not providing enough fuel to support it.
This triggers a cascade of responses that make weight loss much harder than it needs to be. Your body becomes more efficient at conserving energy, reducing non-essential expenditure, and increasing hunger signals, which can make weight loss harder. On top of that, your recovery takes a hit because you aren’t providing as much food as your body wants.
One of the most heartbreaking things is that many triathletes make this even harder than necessary because they have a weight loss goal in mind.
They often reduce the amount of food they eat before and during training, thinking it will help them to lose weight.
But your body is an incredible thing, and it knows that you haven’t eat enough food to support the amount of exercise you’ve just done.
That triggers what I call the monster hunger.
The sort of hunger where you want to devour everything and anything in sight, and you don’t care if it’s slightly gone off yoghurt or your partner’s favourite food.
And unless this is well controlled, this leads to overeating, which is then counter to your weight loss goals.
One of the triathletes inside The Hub, my nutrition membership, noticed this exact issue.
They were going through my complete triathlon nutrition course and showed fantastic insight into how their current approach was actually making it harder to lose weight. They were absolutely right.
They’ve since been increasing their eating before and after, and they’ve found that the cravings are much better later in the day.
The solution framework
So how do we fix this?
Let me share the framework I use with my triathletes.
First, we need to shift your mindset.
The goal isn't to lose weight as quickly as possible — it's to lose weight while maintaining your ability to train effectively.
Setting realistic targets
The first step is setting realistic weight loss targets during Ironman training.
Normal weight loss advice would say that 0.5-1 kilo, or 1-2 pounds per week, is the goal, but for most Ironman athletes, this isn’t feasible.
Instead, aiming for about 0.3-0.5 kilos per week is more realistic and sustainable.
This might sound slow, but remember you're trying to train for one of the hardest endurance events while doing this.
Sure, you might be able to lose more, and some can do this, but it’s not unusual for this to just feel like too much of a struggle and lead to quitting in the long term.
Fueling your training
The next is to fuel your training properly, and this is absolutely crucial.
In fact, like The Hub member I mentioned, you might need to eat more before and during your sessions than you currently do, which often seems counterintuitive at first.
But when you fuel your training properly, you maintain the quality of your sessions, which is essential for your Ironman preparation.
Proper fueling also helps reduce post-exercise hunger, which reduces the chances of overeating later in the day.
You'll recover better between sessions, and perhaps most importantly, you'll break free from the destructive binge-restrict cycle that many triathletes fall into.
Creating your deficit at the right times
Instead of restricting calories at any point, you need to be strategic about when you create your deficit.
Think about your training schedule and create your deficit away from exercise. This means ensuring full fueling before, during, and after your training sessions, while being more mindful of portion sizes at other meals.
On rest days, you might have slightly smaller portions since your energy demands are lower.
However, you should still maintain a high protein intake throughout the day, aiming for 1.6-2.2g per kilogram of body weight.
This helps preserve muscle mass while losing weight and keeps you feeling satisfied despite the calorie deficit.
You can read more about this in this article for triathlon recovery and how much protein a triathlete should eat.
Monitoring the right metrics
You should also monitor different metrics while losing weight, because it isn’t just about the number on the scale.
You need to take a more comprehensive approach to tracking your progress. Pay attention to your training performance — are you maintaining your usual pace, power, and heart rate zones? And what’s your resting heart rate doing?
You can also monitor things like your sleep time and quality, and this isn’t necessarily through your watch but just your self-perceived rating. Is your sleep progressively getting worse?
Finally, check in with your energy levels and your mood. Are you feeling constantly fatigued and drained, or are you snappier and more prone to irritation than normal?
If any of these metrics start trending in the wrong direction, it's a clear sign that you need to adjust your approach.
Common mistakes to avoid
Let me share some of the biggest mistakes I see triathletes make when trying to lose weight during Ironman training, because understanding these can help you avoid some serious pitfalls.
Dramatic calorie restriction
The first and most damaging mistake is dramatic calorie restriction. I see this all the time – athletes think that creating a massive calorie deficit will speed up their weight loss.
This approach almost always backfires.
Your body is already under significant stress from the training load, and when you drastically cut calories, you're essentially forcing it to function on empty.
This often leads to bonking during sessions, poor recovery, and ironically, binge eating later because your body is desperately seeking energy.
My usual advice is to aim for a calorie deficit of about 300-500 per day. This doesn’t sound like much, and it isn’t — but we went through this earlier.
Avoiding carbohydrates
Another crucial mistake is avoiding carbohydrates around training sessions.
Many triathletes have bought into the idea that training in a carb-depleted state will maximize fat burning. While that does, the increase in burning fat for fuel during exercise is not going to make a significant difference in losing body fat, and this is a really crucial point.
Instead, something much worse happens.
Your training quality plummets because you don't have the right fuel source for exercise. Those key sessions – your threshold runs, your race-pace bike intervals, your morning swim training – they all suffer. And when your training quality drops, your overall progress stalls.
Not consuming enough protein
Not consuming enough protein is a mistake that often flies under the radar.
Triathletes tend to focus on overall calories and carbs, neglecting protein intake. During a calorie deficit, protein becomes even more crucial because it helps preserve muscle mass and supports recovery.
When you're trying to lose weight while maintaining performance, you actually need more protein than usual, not less.
So this is where the guidance of 1.6-2.2g of protein per kg of body weight comes in. You should aim for this range every day, and during your longer, harder training days you should be hitting the top end of this range, even a little bit higher.
Extreme diets
I often see triathletes falling into the trap of trying fad diets or extreme "clean eating" challenges. They might try keto, eliminate all processed foods, or follow some influencer's rigid meal plan.
While the motivation is understandable, these approaches are usually far too restrictive for an Ironman athlete.
You need flexibility in your diet to fuel properly, and these rigid approaches often lead to nutrient deficiencies.
They can make it so much harder to lose weight over the long term.
Not monitoring food intake
Another common issue is not tracking food intake accurately. Many triathletes try to "eyeball" portions while attempting to lose weight, but this usually leads to either under- or overestimating intake.
During Ironman training, you need to be more precise — not because you need to track forever, but because it helps you understand your true energy needs and to create an appropriate deficit.
I usually recommend tracking food for a couple of weeks so that you can understand where you’re currently at and where you need to be.
This might not be suitable for everyone, but most will benefit from this to ensure they’re losing weight as optimally as possible.
Too many changes
Finally, many triathletes try to make too many dietary changes at once. They'll simultaneously cut calories, eliminate certain foods, change their meal timing, and alter their training nutrition.
This approach is overwhelming and usually unsustainable. It's much more effective to make one change at a time, let it become a habit, and then consider what else might need adjusting.
For example, focus first on having a good meal before your long sessions, then on how much you’re consuming during your training, and then on your recovery nutrition.
Understanding these common mistakes isn't about being perfect – it's about being aware of potential pitfalls so you can approach weight loss during Ironman training more strategically.
Remember, the goal isn't just to lose weight; it's to do so safely while maintaining your ability to train effectively and improve your performance.
The bottom line
Knowing when to adjust your approach is just as important as the actual process of losing weight. Your body will give you clear signals when your calorie deficit is too aggressive, and learning to recognise these signs early can prevent bigger problems down the line.
All those ones I mentioned in the monitoring metrics section are invaluable here.
We all have bad sessions, we’re all a bit cranky now and then, and sometimes we just sleep badly, and there isn’t a great reason for it.
But when you consistently have poor sessions, consistently sleep badly and feel tired and moody, something isn’t right, and this should prompt you to review your nutrition and training.
The key is to view these signs not as failures, but as valuable feedback from your body.
Often, the solution is as simple as increasing your calories slightly, particularly around training sessions, or redistributing your intake differently throughout the day.
It's always better to make small adjustments early rather than waiting until these signs become serious problems.
The path to weight loss during Ironman training isn’t always easy, but it is possible when you follow the right strategies.
