I'm (currently) a sugar burner, should I care?

Triathlon Forum
1

I recently had resting metabolic rate analysis to satisfy two curiosities: I wanted a better idea of my baseline calorie needs and I was curious what percent fat I’m burning at rest. Turns out, not very much. Only 21% of the calories I burn at rest are from fat.

Should I care? Or make some changes to my diet and training? I think it’s generally agreed that there are benefits to burning a high percentage of fat for fuel, especially for long course racing (preserve glycogen, less reliant on taking in extra carbs).

I suspect a few changes I made to my diet the past ~4 months have contributed to this low fat burn. The two biggest changes were that I reduced the amount of fat in my diet (basically all of which was coming from nuts, peanut butter, eggs, avocado, and/or salmon) and I started fueling more of my workouts with carbs. I made the diet changes in January after reading things like Gustav Iden’s fueling at Daytona and recommendations to cut out fat/fiber/protein while training like in this thread. In February (after adjusting my diet) I tracked my food for two weeks and was generally eating 55-65% carbs, 20-25% protein, and ≤20% fat.

Throughout 2019-2020 I had been doing a fair amount of my morning training before breakfast and had no issue riding 2+ hours on just coffee before and water during. I did plenty of long aerobic rides throughout the pandemic, including a couple 10 hr days and an everesting, fueling mostly with real food and had stable energy throughout. I suspect if I had RMR analysis sometime in the end of 2020 I would’ve been burning a lot hight percent of fat at rest than my test last week.

So bottom line – I’m currently a sugar burner and wondering if it would be beneficial for me to adjust my diet (swapping some carbs with healthy fats) and/or training (easy morning training on just water during and coffee before, fueling longer training with more solid food)? Or does it not really matter in the end?

I’ll mention preemptively that I have no interest in going full HFLC or keto or basically any diet that has an official name. In case it’s helpful context: I’m 41, male, 6’2", 180 lbs, had a DEXA scan in December that put me at 11.9% body fat with zero visceral fat.

2

I’m interested in what the experts say about this as well but I don’t think it matters.

I know if you eat less carbs compared to fats you’ll burn more fats and vice-versa.

3

In general I think things like fat adaptation are really only useful if you’ve got nothing left in terms of normal gains. If you’ve still got meat on the bone of general fitness your fueling should be aimed at helping you succeed in your workouts, which for me is carb heavy but your mileage may vary.

One thing to remember is that being able to burn your own fat stores is a completely different process then being able to digest and metabolize fats you’ve consumed. The two are at best tenuously linked.

Lots of ‘fat adapted’ athletes have done so on high carb diets. Look up Inigo San Millan, Tadej Pogačar’s coach, and maximal fat oxidation training. It seems like having a high fat oxidation level is more a product of having a huge aerobic engine than anything specific done through diet.

4

Should I care? Or make some changes to my diet and training? I think it’s generally agreed that there are benefits to burning a high percentage of fat for fuel, especially for long course racing (preserve glycogen, less reliant on taking in extra carbs).

Nope. Show me studies where fat vs carb burning makes a performance difference and you might need to care but I haven’t seen that yet.

What could matter is what kind of sugar are you burning? One can easily make the argument that for long course racing that slow metabolizing carbs are better than fast metabolizing carbs. Think a product like UCAN/Corn starch vs Gu/surgery drinks. A combo of both is not out of the question either.

5

Probably doesn’t matter much what’s going on at rest. I think it’s been established your body will simply burn whatever fuel you give it and does not translate to more fat burning during exercise. We’re even undergoing glycolysis at rest too. I’m sure we’ll see Dr Alex Harrison chime in here eventually, but he once linked a paper showing substrate usage with carb intake/more intake. Taking in more carbs shows you’ll burn more exogenous carbs thereby burning less fat, but also burning less endogenous carbs.

From a few coaches I’ve found that biggest player in fat utilization would be long aerobic riding and extending your TTE at threshold(therefore extending TTE on everything below FTP)

And from my own personal experience, extending TTE is relatively simple to train but pays dividends when it comes to riding and racing.

6

In general I think things like fat adaptation are really only useful if you’ve got nothing left in terms of normal gains. If you’ve still got meat on the bone of general fitness your fueling should be aimed at helping you succeed in your workouts, which for me is carb heavy but your mileage may vary.

One thing to remember is that being able to burn your own fat stores is a completely different process then being able to digest and metabolize fats you’ve consumed. The two are at best tenuously linked.

Lots of ‘fat adapted’ athletes have done so on high carb diets. Look up Inigo San Millan, Tadej Pogačar’s coach, and maximal fat oxidation training. It seems like having a high fat oxidation level is more a product of having a huge aerobic engine than anything specific done through diet.

Thanks, I’ll check out Inigo San Millan.

Sami Inkinen has written about his experience influencing his % fat burn during exercise. Of course, he appears to have a massive engine and doesn’t appear representative of most athletes. Still found it interesting. Also another data point suggesting that everyone’s different and ymmv, which is part of why I was interested in the RMR analysis in the first place. I’d like to do substrate utilization at different efforts but that’s a more expensive test for another time.

Anecdotally I feel like my daily energy has been fluctuating more since I’ve been higher carb/lower fat.

7

Probably doesn’t matter much what’s going on at rest. I think it’s been established your body will simply burn whatever fuel you give it and does not translate to more fat burning during exercise. We’re even undergoing glycolysis at rest too. I’m sure we’ll see Dr Alex Harrison chime in here eventually, but he once linked a paper showing substrate usage with carb intake/more intake. Taking in more carbs shows you’ll burn more exogenous carbs thereby burning less fat, but also burning less endogenous carbs.

From a few coaches I’ve found that biggest player in fat utilization would be long aerobic riding and extending your TTE at threshold(therefore extending TTE on everything below FTP)

And from my own personal experience, extending TTE is relatively simple to train but pays dividends when it comes to riding and racing.

These are both interesting and make me even more curious about my substrate utilization during exercise.

8

https://journals.physiology.org/doi/full/10.1152/ajpendo.00376.2015
Glucose vs Sucrose(glu and fru) vs control

Still poking around looking for the endogenous vs exogenous

.

9

I recently had resting metabolic rate analysis to satisfy two curiosities: I wanted a better idea of my baseline calorie needs and I was curious what percent fat I’m burning at rest. Turns out, not very much. Only 21% of the calories I burn at rest are from fat.

Should I care? Or make some changes to my diet and training? I think it’s generally agreed that there are benefits to burning a high percentage of fat for fuel, especially for long course racing (preserve glycogen, less reliant on taking in extra carbs).

I suspect a few changes I made to my diet the past ~4 months have contributed to this low fat burn. The two biggest changes were that I reduced the amount of fat in my diet (basically all of which was coming from nuts, peanut butter, eggs, avocado, and/or salmon) and I started fueling more of my workouts with carbs. I made the diet changes in January after reading things like Gustav Iden’s fueling at Daytona and recommendations to cut out fat/fiber/protein while training like in this thread. In February (after adjusting my diet) I tracked my food for two weeks and was generally eating 55-65% carbs, 20-25% protein, and ≤20% fat.

Throughout 2019-2020 I had been doing a fair amount of my morning training before breakfast and had no issue riding 2+ hours on just coffee before and water during. I did plenty of long aerobic rides throughout the pandemic, including a couple 10 hr days and an everesting, fueling mostly with real food and had stable energy throughout. I suspect if I had RMR analysis sometime in the end of 2020 I would’ve been burning a lot hight percent of fat at rest than my test last week.

So bottom line – I’m currently a sugar burner and wondering if it would be beneficial for me to adjust my diet (swapping some carbs with healthy fats) and/or training (easy morning training on just water during and coffee before, fueling longer training with more solid food)? Or does it not really matter in the end?

I’ll mention preemptively that I have no interest in going full HFLC or keto or basically any diet that has an official name. In case it’s helpful context: I’m 41, male, 6’2", 180 lbs, had a DEXA scan in December that put me at 11.9% body fat with zero visceral fat.

After spending more than a decade testing some of the best Ironman athletes in the sport, I can confidently say that the ability to oxidize high levels of fat at race pace is the most important physiological quality that a long distance athlete can possess. Far more important than having a high VO2max or threshold (these qualities are often quite modest, by elite standards, even for athletes with Ironman wins under their belt).

There are plenty of athletes who do well at short course racing with sub-par fat oxidation but **every **top level Ironman athlete that I tested had very strong fat-burning abilities relative to their size.

FWIW, I don’t think a full keto approach is necessary or even ideal & that small shifts in every day macronutrient composition, along with the right type of training can amount to large shifts in fat oxidation at race efforts.

10

After spending more than a decade testing some of the best Ironman athletes in the sport, I can confidently say that the ability to oxidize high levels of fat at race pace is the most important physiological quality that a long distance athlete can possess. Far more important than having a high VO2max or threshold (these qualities are often quite modest, by elite standards, even for athletes with Ironman wins under their belt).

There are plenty of athletes who do well at short course racing with sub-par fat oxidation but **every **top level Ironman athlete that I tested had very strong fat-burning abilities relative to their size.

FWIW, I don’t think a full keto approach is necessary or even ideal & that small shifts in every day macronutrient composition, along with the right type of training can amount to large shifts in fat oxidation at race efforts.

I feel like there’s a difference between something being a useful performance marker, and something being both a marker and an attribute an athlete should try to directly train.

A dumb analogy would be yasso 800s, if someone is doing proper marathon prep their interval times will drop and it can be used as a good performance predictor. But going off and doing a bunch of work targeted at 800 repeats isn’t going to improve your marathon time even though the 800 time will improve significantly.

Applying the same to Fatox, I’m not sure if it’s something an athlete should try to directly train or if a high fatox is ‘only’ useful as a marker that an athletes endurance base has been really well developed.

11

After spending more than a decade testing some of the best Ironman athletes in the sport, I can confidently say that the ability to oxidize high levels of fat at race pace is the most important physiological quality that a long distance athlete can possess. Far more important than having a high VO2max or threshold (these qualities are often quite modest, by elite standards, even for athletes with Ironman wins under their belt).

There are plenty of athletes who do well at short course racing with sub-par fat oxidation but **every **top level Ironman athlete that I tested had very strong fat-burning abilities relative to their size.

FWIW, I don’t think a full keto approach is necessary or even ideal & that small shifts in every day macronutrient composition, along with the right type of training can amount to large shifts in fat oxidation at race efforts.

I feel like there’s a difference between something being a useful performance marker, and something being both a marker and an attribute an athlete should try to directly train.

A dumb analogy would be yasso 800s, if someone is doing proper marathon prep their interval times will drop and it can be used as a good performance predictor. But going off and doing a bunch of work targeted at 800 repeats isn’t going to improve your marathon time even though the 800 time will improve significantly.

Applying the same to Fatox, I’m not sure if it’s something an athlete should try to directly train or if a high fatox is ‘only’ useful as a marker that an athletes endurance base has been really well developed.

As I understand it, endurance training in and of itself is one of the most effective ways to increase fat oxidization. Based on that certainly stands to reason that people doing high volumes of endurance training would be correlated to a higher fatox, but i’m not sure that necessarily points at diet being the cause- especially as it seems to be at odds with a pretty strong scientific consensus in support of a high-carb diet and the way most long-course pros seem to eat. (Though I understand the latter is notoriously unreliable.)

To speak to the OP’s case more directly, it seems like you’ve got a pretty healthy/balanced diet either way, so I don’t think there would be much harm in a slight shift in macronutrient composition outside of training. However, at this point, I don’t think there’s sufficient evidence to support doing so from a performance standpoint.

12

Applying the same to Fatox, I’m not sure if it’s something an athlete should try to directly train or if a high fatox is ‘only’ useful as a marker that an athletes endurance base has been really well developed.

I’m not going to question Alan’s learned analysis.

But I agree with your statement here.

Reading here and elsewhere and listening to more than a few “experts” talk about this, one would think it’s as simple as, that you can some how adjust fuel and substrate usage like you are adjusting the knobs on a stereo system! It’s an intricate and complicated system and the vast majority of Age Group triathletes, would be better to work at overall volume of training, and total endurance fitness, over years and years, and if changes happen in your body - then so be it!

13

How do you eat that many carbs? What’s your gram count?

14

After spending more than a decade testing some of the best Ironman athletes in the sport, I can confidently say that the ability to oxidize high levels of fat at race pace is the most important physiological quality that a long distance athlete can possess. Far more important than having a high VO2max or threshold (these qualities are often quite modest, by elite standards, even for athletes with Ironman wins under their belt).

There are plenty of athletes who do well at short course racing with sub-par fat oxidation but **every **top level Ironman athlete that I tested had very strong fat-burning abilities relative to their size.

FWIW, I don’t think a full keto approach is necessary or even ideal & that small shifts in every day macronutrient composition, along with the right type of training can amount to large shifts in fat oxidation at race efforts.

I feel like there’s a difference between something being a useful performance marker, and something being both a marker and an attribute an athlete should try to directly train.

A dumb analogy would be yasso 800s, if someone is doing proper marathon prep their interval times will drop and it can be used as a good performance predictor. But going off and doing a bunch of work targeted at 800 repeats isn’t going to improve your marathon time even though the 800 time will improve significantly.

Applying the same to Fatox, I’m not sure if it’s something an athlete should try to directly train or if a high fatox is ‘only’ useful as a marker that an athletes endurance base has been really well developed.

I would agree with you if it wasn’t for the numerous athletes that I saw improve their Ironman performance in concert with changes to their nutrition and training to improve fat oxidation.

One particular pro comes to mind who was a very good ITU athlete making the move to 70.3 and underperforming over the longer events. His max fat oxidation initially tested at 3kcal/min (pretty horrible for an elite). With a change in diet (more fat) and training (more low intensity work), his fat ox doubled to 6kcal/min at race power and his performance in 70.3 racing exceeded his performances in his short course events (several wins) & he went on to be a pretty solid Ironman athlete as well.

This wasn’t an isolated example. In fact, I’d say it was fairly typical of athletes who came to me underperforming over the long races who were able to turn it around.

15

I don’t think we disagree too much, if at all. My statement was hedged with “I’m not certain”, and I’ve got experience with approximately one athlete, myself haha.

More that I come from an IT background and there’s a saying “every measurement becomes a target”, about useful metrics being turned into bad targets. I’m reminded of that when I see folks base their training off of a single metric. I agree with the value of Fatox as a metric, but I’m not sure of it as a target.

If your advice for training fatox is “train a larger volume of lowered intensity, and eat healthy” then I have no disagreements. That’s solid advice for any long distance athlete, even if they aren’t targeting fatox.

16

If increase in fat oxidation is so good for performance why do we never see this in the scientific studies? Consistently it’s found no improvement in performance with “fat adaptation”. We’ve had studies where the carb group out performed the fat adaptation group as limiting their carb intake decreased training ability. There’s also some evidence that become highly fat adapted leads to reduced glucose tolerance and a delayed insulin peaks following sugar consumption - which are probably not ideal for those that plan to use carbs on race day (for which there is a huge amount of scientific support for).

Also the idea you can train it is imo a bit misleading. Really the only way to achieve fat adaptation seems to be through high fat low carb diet. For example this study found that fasted exercise increased fat oxidation, however as soon as you start eating carbs again you go back to baseline https://journals.physiology.org/doi/full/10.1152/japplphysiol.01195.2007

Of course lots of low intensity training will increase mitochondria in muscles, which will allow for more fat oxidation. Combined with huge vo2 max likely explains why elite endurance athletes may have high rates of fat oxidation. Seems like a case where correlation doesn’t = cause (i.e. increasing fat oxidation alone won’t improve performance - as demonstrated by the studies).

17

The glycogen in your liver can last for about 48 hours so everyone is a sugar burner until that is depleted.

If you want to go to a fat burner, fast for 48 hours so your body uses up the stored glycogen and then your only source of fuel is fat which your body (particularly your brain) will burn.

18

Also the idea you can train it is imo a bit misleading. Really the only way to achieve fat adaptation seems to be through high fat low carb diet. For example this study found that fasted exercise increased fat oxidation, however as soon as you start eating carbs again you go back to baseline https://journals.physiology.org/...plphysiol.01195.2007

Of course lots of low intensity training will increase mitochondria in muscles, which will allow for more fat oxidation. Combined with huge vo2 max likely explains why elite endurance athletes may have high rates of fat oxidation. Seems like a case where correlation doesn’t = cause (i.e. increasing fat oxidation alone won’t improve performance - as demonstrated by the studies).

Aren’t these two statements somewhat in conflict? If you can increase mitochondria through training and that increases fat oxidation, isn’t that a means of achieving fat adaptation? It’s just that the dietary means of becoming fat adapted aren’t very useful.

19

After spending more than a decade testing some of the best Ironman athletes in the sport, I can confidently say that the ability to oxidize high levels of fat at race pace is the most important physiological quality that a long distance athlete can possess. Far more important than having a high VO2max or threshold (these qualities are often quite modest, by elite standards, even for athletes with Ironman wins under their belt).

There are plenty of athletes who do well at short course racing with sub-par fat oxidation but **every **top level Ironman athlete that I tested had very strong fat-burning abilities relative to their size.

FWIW, I don’t think a full keto approach is necessary or even ideal & that small shifts in every day macronutrient composition, along with the right type of training can amount to large shifts in fat oxidation at race efforts.

I would agree with you if it wasn’t for the numerous athletes that I saw improve their Ironman performance in concert with changes to their nutrition and training to improve fat oxidation.

One particular pro comes to mind who was a very good ITU athlete making the move to 70.3 and underperforming over the longer events. His max fat oxidation initially tested at 3kcal/min (pretty horrible for an elite). With a change in diet (more fat) and training (more low intensity work), his fat ox doubled to 6kcal/min at race power and his performance in 70.3 racing exceeded his performances in his short course events (several wins) & he went on to be a pretty solid Ironman athlete as well.

This wasn’t an isolated example. In fact, I’d say it was fairly typical of athletes who came to me underperforming over the long races who were able to turn it around.

Thanks Alan, always interesting to hear your thoughts and experiences.

With no races last season I put in the largest volume of low intensity riding I’d ever done before. Nowhere near pro-level but it included a solid 6 month block averaging ≥15 hr/week of riding, plus a bit of running and some strength work (no swimming, my pool was/is closed). Pre-COVID I was racing long course for several years and have been generally training for endurance events for almost twenty years now, so I’d like to think I have a reasonable fitness base.

You mention that small shifts in macronutrient composition can amount to large shifts in fat oxidation – do you think it’s reasonable that going higher carb/lower fat could’ve shifted my ability to burn fat in just 4 months, despite several seasons of aerobic base? I’d hate to think I was burning even less fat at rest before I increased my aerobic training volume!

Also, I’d assume that if I’m only burning ~21% fat at rest then that percent isn’t going to increase as I start exercising, but that could be a very naive assumption. Is it possible for a person to burn more fat for fuel as they’re exercising than when they’re at rest?

20

One particular pro comes to mind who was a very good ITU athlete making the move to 70.3 and underperforming over the longer events. His max fat oxidation initially tested at 3kcal/min (pretty horrible for an elite).

Re-reading this kind of sounds like he had aerobic deficiency syndrome. At Olympic distance a good athlete is going to be predominantly around/slightly above threshold, you can get by without a huge aerobic base (of course it helps!). Key is dealing with lactic acid. Once you go to longer distances you need that base, because you can’t rely on anaerobic system for that long.

Although not triathlete focused uphill athlete have plenty of examples of guys like this. Crushing half and marathon distance then they get in the lab and realise their aerobic threshold is actually very poor and their superiorly developed anaerobic system has been pulling them through. Which works until you get into longer events. The fix - lots of low intensity miles, which increases mitochondria meaning more fat oxidation, and ability to sustain better pace while maintaining below aerobic threshold. The solution was not changing fat oxidation itself (if that worked we could all just eat high fat low carb and watch our performance increase overnight), but increasing mitochondria allowing for more fat oxidation.