First Ironman and going fat adapted

Hi all, Long term TR user but newish to the forum. Apologies if this has been covered elsewhere, I couldn’t find any answers in the search function…

I’ve just signed up for my first ironman (Copenhagen '20). Planning on following the low volume full training programme of base, build, specialty with a couple of float weeks for ‘life’. This has me starting the training cycle in late Jan. I’m just heading into CX specialty, and will be coming out of that at the end of November, which gives me 8 weeks of not much. I’m planning on using those 8 weeks to do some trad base on the bike to keep things ticking over (along with the odd run and swim too, peppered with some strength work.

FTP is currently 275 and pretty sure I can get back to 325 (have been as high as 340 but when cycling only). I am however, looking to sort my fueling out for the ironman now. I’ll be competing against a couple of friends and my brother, so I must crush them. Given I’ve got 8 weeks to play before starting the training cycle, I’m considering using this time to go ‘fat adapted’. My rationale is that 8 weeks of trad base and LCHF will give me time to adapt before taking on the harder workouts that come with the full plan. Is this wise? Can I expect to get from 275 to 325 as fat adapted, and will this strategy stop me from hitting the wall and exiting the event stage left? Will I be quicker/more resilient fat adapted than I would be if I were more carb dependent with a higher FTP? Would also ask for resources to help go fat adapted if sensible, there’s a fair few books around, but recommendations are always better than going blind…
I’m planning on training low, but racing high when it comes to carbs, so won’t rely solely on my butter.
Other bits to consider, I’m 42, several years of riding (1 year of tri) behind me and have previously stuck to TT’s. I’ve a high stress exec job and family with youngish kids, although can generally squeeze a morning session and evening session into most days (helps separate work out from homelife and family are super supportive). Currently 83kg, will target 75kg for the day.

Going LCHF is a great way to reduce your ability to train optimally. It’s like driving around all day in your car with the handbrake on.


Trad Base and LCHF are both very long term strategies, think years. Unfortunately, that’s how long it takes to i) build and benefit from long, low intensity endurance work, and ii) for the body/liver to morph into a truly fat adapted system. Pursuing both for only 8 weeks before starting “real training” is just going to mess up that future training.

Plus this:

Genuine Trad Base requires a LOT of hours, like 15+hrs/week in order for it to produce meaningful results. It kinda sounds like you don’t have the time, although doing less LSD won’t necessarily add any more stress to what seems like an already stressful life.

By all means, start now, but then shift your A-race to 2021. Or, like @Berggeiss suggested, stay on the carbs and keep doing shorter, higher intensity work.

This point was discussed in one of the TR podcasts (sorry, I don’t remember which one). And I think Chad specifically advised against a low carb, high fat diet, because it decreases your ability to train. Raising your FTP still seems the way to go here as well as the perennial “fuel your workouts”.

I wouldn’t recommend it. I’m sure there are outliers out there, but a HFLC diet when training for an event like this, I think you’re going to limit your performance because even if you plan to race high, you’re going to limit your ability to train effectively with that limited diet.

I’ve done it, went through the carb flu, got out of it… was able to train pretty well… and then still had my worst season of racing. It didn’t work for me. It could work for you, but IMO trying to go Keto/Fat-adapted and high endurance athletic performance don’t go hand-in-hand for most of us, particularly those with challenging lifestyles outside of our training.

What is your diet like at the moment? Do you eat a high % of carbs, or do you already eat a lot of fat? Unless your diet is or has always been fairly low in carbs, I wouldn’t drastically change it to go LCHF. Even if that strategy was useful long-term, it will take you more than 8 weeks to adapt.

If you had previous success with a carb-based diet, I wouldn’t change that approach now.

I’d also warn about the impact on the rest of your life. Carb depletion can make you grumpy, stressed, and tired. That doesn’t seem to combine well with a high-stress job…

I was just a miserable cuss when I was “fat-adapted”; my wife noticed the change for the worse. When I eat enough and eat carb-focused while training, I’m way… WAY happier.

I’m only planning the trad base for 8 weeks as I have that time ‘free’ and feels like it would be the time to attempt to start the switch and give me something to do. After those 8 weeks, I’m planning to follow the plans for the full distance. It was my intention to try the full plans LCHF, though the feedback so far is a resounding ‘don’t do it’ (Not disregarding that feedback, just trying to understand all sides of the coin).

I’ve only just started tracking macros over the last couple of weeks to see how my diet is normally. (I’ve been doing Short power build with additional runs and swims for the last 8 weeks). My diet doesn’t appear to be much of anything. 50% carb, 30% fat and 20% protein. It can definitely do with a sharpening up.

I think I remember this, though I keep thinking back to last year’s Kona episodes with TR users and sure they all advocated a LCHF diet? Didn’t Chad suggest there was a place for it in long endurance lower intensity type races?

I wonder if trying it for 8 weeks during a mini trad base block will give me enough feedback to know if it’s long term sustainable for taking on the full training plans? I’f I’m struggling it will show pretty quickly? And 8 weeks must be long enough to start to see some adaption? I’m pretty sure the wife will let me know if I’m too grumpy within about 2 minutes. :wink:

That or I buy shares in Maurten…

I think “fat adapted” is one of the most misunderstood buzzwords amongst endurance athletes. Yeah, chronically restricting CHO forces your body to rely more on fat as an energy source. However, It doesn’t make you a better athlete, it does reduce your ability to train and cope with heavy training loads. It has been shown to impair glycolysis, which you definitely don’t want. There may be some benefit gained from periodising your carb intake, but even then, there’s better ways to force adaptions.


My take on the fat adapted thing is that it really only has benefits that outweigh the drawbacks for ultra distance type athletes. People that are running 100 miles a day, or the cycle race across europe in a week. In that instance, I’ve got to imagine getting fuel in is almost more important than firness…and you can only go so hard over thousands of miles in a week anyway, so fat adaption might be viable.

But even then…would it be better than just traing hard, with carbs, at higher intensities?

I’d have to go back and listen again to be sure, but I don’t remember that. One thing that’s struck me about all the pro/elite interviews is that they all seem to eat oatmeal of some variety for breakfast, and most all are carb-centered dieters.

I know a few endurance athletes who claim to be fat-adapted, and they are generally Ultra runners or hikers, etc. I think there is a place for it, and I think you can complete ultra-distance events fat-adapted, but I do not think it lends itself to optimal performance in competition.

I know from my own self-experiment that it is a suboptimal diet for me, granted the season I did it I was not racing 140.6.

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So true - when training for Ironman - if we had to go anywhere as a family, my wife would packs snacks for me, and the kids. A bag of gold fish for the kids and one for Dad. During conversations she would often say “go eat something” as I could get grouchy fast! Can’t imaging trying it on LCHF.


Yup, there is — Enduro and/or 24hr.

If you aren’t training or racing those type of sub-sub-threshold events — which tri isn’t…I guess that answers that question.

Perhaps, but probably quite a low level of “some”, especially if you don’t have the time to put in 15+ hours/week doing Endurance rides. I’ve read (don’t remember where) that it takes ~12 weeks to see “gains” in mitochondria via low intensity work. Are you going to get more out of 8 weeks of Z2/HFLC training or 8 weeks of hi-carb sweet spot work?

Do a Goog on Lionel Sanders, a world class tri guy who tried HFLC for a season and failed miserably (sound familiar, Ms. Batty?). So you have one athlete doing long multi-hour steady state races and another athlete doing hour-long power spike races…and HFLC has not worked in either example.

Lastly, give this a listen:

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What do you mean by Enduro? Certainly you don’t mean MTB?

Enduro MTB requires a lot of anaerobic power.

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“Enduro” is the worst misnomer in cycling. Not that endurance isn’t required, it just completely misleads by its name.

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My faux pas, gents. I meant ‘enduro’ with a small ‘e’ as a catch-all for ultra-endurance/distance, e.g. RAAM.

Now back to tri, of which I also have no first-hand experience! :confounded:

8 weeks should be enough time to get over the initial adaptation period. It’s really a thing, your workouts will suffer, but it does pass and you’ll be right back where you left off when it does. Extra sodium supplementation can help – maybe. You definitely can go from 275 to 325. I’ve been LCHF for a number of years now, and last tested 323W, up from 220W in Feb 2018 (when I started TR). I primarily race cross, and last season was great. I didn’t carb-up for cross races, but any road stuff >60miles I will use them in-ride. There aren’t a lot of great resources for sports and this way of eating. Maybe the reddit ketogains forum, although I always got the impression it was more for weight lifting than endurance sport. A lot of the science is done with either athletes that have already demonstrated huge success with carbs (a survivorship bias), or else was too short to get over the adaptation period (designed to fail…). LCHF will definitely help you with losing a few pounds right away.

The real crux of your question is “should I? will I get faster?”. That’s impossible to answer. If bonking is your biggest problem, it might actually make you faster, but only because you won’t have to eat/drink insane amounts of carbs during the race, or stop to empty the bowels every 20 minutes. There’s a lot of evidence LCHF reduces inflammation, and anecdotal reports that workout recovery is greatly improved. I would say I feel my recovery is improved. This may allow you to train more… but that only matters if you do train more than if you were carb’ing it up.

From my notes (source lost to the wind):

Fat can only be “burned” in mitochondria, so the observed increase in fat-oxidation capacity corroborates an increase in mitochondrial function as a result of increased Z2 training.

It all comes back to if you can do enough Z2/Endurance hours. If you can’t, then best to call it a day and continue with high carb HIIT.

LCHF has no advantage over any other “diet” in regards to weight loss or inflammation. There is zero scientific evidence to support such claims. A calorie deficit is what causes weight loss. A calorie deficit also has positive effects on inflammation.

Edit: Somehow I quoted the wrong person…

I distinctly remember that they advised against a LCHF diet. Apparently, it only seems to be helpful for athletes involved in ultra endurance events, people for whom a marathon is a walk in the park.