What happens when fat stores are depleted?

[cbrunny]

This might be silly, and a completely ridiculous question.

My situation: when I was younger I was an endurance athlete. I never really performed fast but I could outlast pretty much anyone. I was involved in triathlon from about 17 to about 23, and that's where this really showed the most.

I'm now 29 and had gained quite a bit of weight. At 17 I was ~140 lbs. At 26 I was 212. At 29 I'm (as of this morning) 172. It's falling off now because I'm getting back into swim/bike. No run yet (that would be a different thread). I'm finding the endurance component has come back super fast - way faster than I had expected it to. And with that is also now starting to come speed over distance that I never had before. I'm still far from fast but I'm noticing gains that I just shouldn't have. It's confusing.

But I have a lot of fat stores right now. Im 5 ft 6, and depending on the measurement tool somewhere between 23% and 34% body fat.

I'm thinking my body is unusually good at metabolizing fat during a workout. So what happens if I reach a percentage around 8%? Will my performance actually decrease as a result of having less body fat? I expect that as the BF% declines, the amount I metabolize in a training session will decrease and the amount of glycogen stores consumed will increase. If my glycogen stores do not increase at the same or greater rate than my body fat declines... what happens?

Does that make any sense? Or is this just nonsensical rambling?

 

[Zivic]

This might be silly, and a completely ridiculous question.

My situation: when I was younger I was an endurance athlete. I never really performed fast but I could outlast pretty much anyone. I was involved in triathlon from about 17 to about 23, and that's where this really showed the most.

I'm now 29 and had gained quite a bit of weight. At 17 I was ~140 lbs. At 26 I was 212. At 29 I'm (as of this morning) 172. It's falling off now because I'm getting back into swim/bike. No run yet (that would be a different thread). I'm finding the endurance component has come back super fast - way faster than I had expected it to. And with that is also now starting to come speed over distance that I never had before. I'm still far from fast but I'm noticing gains that I just shouldn't have. It's confusing.

But I have a lot of fat stores right now. Im 5 ft 6, and depending on the measurement tool somewhere between 23% and 34% body fat.

I'm thinking my body is unusually good at metabolizing fat during a workout. So what happens if I reach a percentage around 8%? Will my performance actually decrease as a result of having less body fat? I expect that as the BF% declines, the amount I metabolize in a training session will decrease and the amount of glycogen stores consumed will increase. If my glycogen stores do not increase at the same or greater rate than my body fat declines... what happens?

Does that make any sense? Or is this just nonsensical rambling?

8% is pretty darn lean. not too many people are reaching those levels......

short answer, yes, your performance will decrease if you get too lean

 

[cbrunny]

8% is pretty darn lean. not too many people are reaching those levels......

short answer, yes, your performance will decrease if you get too lean

just to be clear, i'm not aiming for any specific fat percentage. Just pondering.

 

[deadlyapp]

I see no reason why your performance would decline if you reach an ultra-low BF% provided you feed yourself enough to maintain at that BF%. If you are metabolizing more than taking in, then yes, your body should start cannibalizing your muscle mass which would affect your performance over time.

 

[Zivic]

I see no reason why your performance would decline if you reach an ultra-low BF% provided you feed yourself enough to maintain at that BF%. If you are metabolizing more than taking in, then yes, your body should start cannibalizing your muscle mass which would affect your performance over time.

can make a huge difference depending on the task at hand.

I was sub 6% for a while and I felt horrible. the difference in just 4-5 lbs moving up to 8-9% was dramatic and staying in the 10-12% range even better. strength is impacted, stamina, overall mental clarity and concentration.... getting lean is something that comes naturally to some, but if you aren't one of those people and get lean, it can greatly impact your physical, and mental performance

 

[hightree]

So what happens if I reach a percentage around 8%? Will my performance actually decrease as a result of having less body fat? I expect that as the BF% declines, the amount I metabolize in a training session will decrease and the amount of glycogen stores consumed will increase. If my glycogen stores do not increase at the same or greater rate than my body fat declines... what happens?

Do you have any source that says that glycogen stores increase when your body fat stores decrease?

I'm currently not aware of this. Your maximal glycogen stores are pretty much the same all the time. With very low body fat, you might burn glycogen (and muscle protein) faster.

There's one trick to temporarily increase glycogen stores: you empty your glycogen stores completely by heavy exercise (to burn 2k+ Calories) and then eating carbohydrate foods. Your new glycogen stores would be then greater than initially.

 

[gar655]

"What happens when fat stores are depleted?"

As asked, the answer would be- death.

The top tri guys are in the single digits for body fat and seem to do just fine at ironman distances.

 

[Ancalagon44]

Do you have any source that says that glycogen stores increase when your body fat stores decrease?

I'm currently not aware of this. Your maximal glycogen stores are pretty much the same all the time. With very low body fat, you might burn glycogen (and muscle protein) faster.

There's one trick to temporarily increase glycogen stores: you empty your glycogen stores completely by heavy exercise (to burn 2k+ Calories) and then eating carbohydrate foods. Your new glycogen stores would be then greater than initially.

Athletes tend to be able to store more glycogen than untrained individuals.

OP - no, not necessarily. 8% body fat would still provide enough for an endurance run. The important thing is how good your body is at using fat for exercise as opposed to glycogen. Sounds like your body is already fat adapted, which is great.

As others have said, the only problem you might face is if you do reach 8% body fat, do a lot of endurance exercise, but don't eat enough to replenish your energy. Then you would probably crash quickly.

 

[Carson Dyle]

I'm thinking my body is unusually good at metabolizing fat during a workout.

What leads you to believe that?

So what happens if I reach a percentage around 8%? Will my performance actually decrease as a result of having less body fat?

At 8%? Unlikely, unless you've recently been starving yourself, or it's very difficult for you to maintain that level.

 

[cbrunny]

I think I need to understand better the science of endurance sports. This thread is helpful. Thanks for the comments.

I do not expect to hit an 8% BF. If I am able to get running again injury free, I might hit ~13%. But not really sure.

 

[bradley]

can make a huge difference depending on the task at hand.

I was sub 6% for a while and I felt horrible. the difference in just 4-5 lbs moving up to 8-9% was dramatic and staying in the 10-12% range even better. strength is impacted, stamina, overall mental clarity and concentration.... getting lean is something that comes naturally to some, but if you aren't one of those people and get lean, it can greatly impact your physical, and mental performance

Agreed 1000%. I was down to 7% and felt like absolute crap with sub-optimal energy levels. Eventually my endocrine system was impacted and started to feel flu-like symptoms. The only thing that helped was consuming way more fats, especially coconut oil. Now I drink around 4 ounces of coconut oil daily and have hovered around 7.5% to no ill effects. And I'm stronger than ever. Plus I have amazing gallbladder health now. lol