Fat burner vs. carb burner


every now and then, I hear about carb burning vs. fat burning athletes. It’s an interesting topic for me but I didn’t find answers to these questions:

  • How do I know which type of metabolic type am I?
  • What should I eat to lose weight and keep the perfomance high based on my metabolic type?
  • How do I fuel my hard races and granfondos based on my metabolic type?

Any suggestions?




Hey Riccardo!

Great question and definitely an interesting topic. I’ll definitely expand on this in more depth in a future offseason weight loss/winning in the kitchen pod w/ @FRANK :wink:

In a nutshell: we’re never only burning just carbs or just fat, it’s always a mixture depending primarily on 1. intensity of exercise 2. duration of exercise and 3. diet. The only way to truly know where you skew though, because it’s true that some of us burn more carbohydrates at a given relative intensity, is to do a metabolic test, also known as an RER test.

As far as weight loss goes, you want to eat a well rounded, nutritiously dense diet for a long time. You have to make it a sustainable and a long term process. We’ve talked about this on a number of podcasts and we’ll probably cover it again soon! But in my opinion, as far as overall diet goes, the quality of the carbohydrate and fat sources is much more important than the quantity or relative percentage of the macronutrient breakdown. So don’t worry too much about it right now, focus instead on dialing in the general quality of the diet first and then start to tweak the amounts based on your training and racing goals.

Apologies if this is vague or confusing, it’s a little hard to explain in a post! But like I said, I will expand in more detail in a future podcast so stay tuned! Thanks for the great Q though!


Dear Jackson,

thank you for your answer, very interesting and inspiring as usual!
Looking forward the new FasCat podcast on nutrition!


I look forward to more feedback on this issue. I also think there is more information and studies on the subject today. With all of the Keto dieting out there.

In the off season, as a master cyclist, I’ve trained my body to be in a fat burning mode to get down to race weight. I’m also looking a the benefits of fat burning on endurance races. My energy stores last me to about 50 miles.

Whether you use carbs or fat for energy you are still going to have to burn fat to lose weight. After several coaches, they always want you on a high carb diet for performance. Once you eat carbs then your body doesn’t want to go back to burning fat for a week and it messes up my system. Just staying on a fat diet to lose weight is much easier, less complex and it drops the cravings once off of carbs.

Right now I can burn fat for energy. I hope as I lean out that carbs will become a more important part of the diet.

How do you get your coach to let you stay on fat diet for energy until you are at your race weight?

Should I just quickly lose the weight to avoid the coaching conflict?

Before you say nutritionist. I’ve worked with a nutritionist in you past that just left me starving in the evenings. What nutritionist say about a fat diet to lose weight?


Kevin –

Indeed the data on high fat diet (HFD) and keto diet in endurance athletes is growing.

Sounds like you’re enjoying the weight loss you’re seeing on a HFD. Agreed that one must burn fat to lose weight as an athlete. A weight loss of 1-2 lbs per week is considered a healthy rate that will not compromise your training.

When you mention the benefits of fat burning on endurance races, mixed data indicate genetics, gender, and other factors determine success, whereas carbohydrates consistently show efficacy,

Carbs are needed for high intensity/race performance and for really getting maximum watts out of your body. Muscles still work on glycogen, and recent data show that fat-based diets “…do not improve training capacity or performance, but directly impair rates of muscle glycogenolysis and energy flux, limiting high-intensity ATP production”. Also “When highly trained athletes compete in endurance events lasting up to 3 h, CHO-, not fat-based fuels are the predominant fuel for the working muscles; CHO, not fat, availability becomes rate limiting for performance.”

I’d love to learn more about your comment “Once you eat carbs then your body doesn’t want to go back to burning fat for a week and it messes up my system”. It could be the type of carbs you’re choosing, and when you’re eating them. I have a very fueling-based approach to carbs, and am not a proponent of ‘just eat a high-carb diet’.

In addition, HFD/keto excludes all plant compounds important for recovery, microbiome, etc. Polyphenols (incl flavonoids & anthocyanins) help lessen oxidative damage. Keto excludes the fruits and vegies that have polyphenols important for recovery, strong microbiome, etc. I’d love to hear if you are integrating fruits and vegies into your diet.

I do like your comment “Right now I can burn fat for energy. I hope as I lean out that carbs will become a more important part of the diet” – this sounds like a reasonable approach, with some caveats (ie when in the season you’re fat-burning – off season? And which carbs and when, so you avoid putting the weight back on).

I also would like to learn more about your blood biomarkers; how are your lipid profiles looking? We want to make you a health person as well as a fast bike racer!

Thanks for contributing to the forum!
Coach Dr. Lauren



The data that you are commenting on, is very helpful to back up our conversation. It is nice to know where the science is going. I appreciate your reply on the information.

I don’t want to label me or lock me into a KETO or HFD but I’m on a fat burning diet. I’m forcing the body to burn fat for energy and still limiting the fat intake. I’m cutting out most carbs if I want to burn body fat. It maybe the same thing a Keto’s because I’m putting myself in a KETO’s state but without the added fat calories. Since the body is already burning fat for energy. My body has less of a problem burning body fat vs burning consumed fat. I do also take in proteins and reasonable amount of health vegetables. I have been avoiding most fruits because of their high fructose(carb) levels and carbs in general because the body will always burn carbs before it will burn fat or protein.

The tricky is trying to work in carbs back into my diet for use as cycling energy and performance. I agree unless I have my body trained to burn fat first and I’m doing long endurance rides in Zone 2, I need the carbs for +zone 2 efforts. Right now, I’m trying to just use carbs that are used up during a workout. Races will be a different plan. To me it is hard to switch between fat and carb burn modes. Carbs also cause energy spikes and energy crashes. Where fat burning seems to keep me on a steady energy level. Where fat stores are used to make energy that is not consumed.

When I burning fat I seem to have much less craving for food. I have seen some studies on continues glucose monitoring of people on fat diets that show glucose swings only when they workout. This supports what I seem to be feeling. I get much more hunger swings from carbs; whether it’s from the bug in the stomach wanting more sugar/their food or because of the glucose swings.

During off season I want to burn the fat or until I get to my target weight. I don’t want a restricted diet while racing that cause me to bonk or not recover quick enough.

I am concerned that the carb diet was causing the bad Lipid level but fat can to or even worse. I have dropped the levels since I have been monitoring them. As my age group is getting thinned out with health issues. I think staying heart healthy is key factor. Keeping arteries open will allow more unrestricted blood flow. We have all seen way too many cyclists have heart issues while cycling. If you pass out on a hot day and the EMT show up. What is the first think they think?

Here are my Lipid
Fat Protein Diet;
Date Weight Try HDL LDL
1/3/22 204 40 81 199 Ketones 3+
2/1/22 194 37 81 145 Apolipoprotien B 109

I hope this is helpful!


Sounds like your strategy is working for you. It will be useful for me to see the foods you’re eating so I have a better picture. More info will be in the Nutritional Analysis I’ll be doing for you next week! :+1:t2: