2

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Stored body fat.... PROOF humans are fat burners??

Answered on August 19, 2014
Created July 15, 2012 at 2:29 AM

Got to thinking today (dangerous for me...lol)! To me, the very fact that the human body converts excess sugar (read excess carbs) or calories into adipose tissue (read fat) is biological proof that the human genome has adapted to burn fat as the most efficient fuel. If evolution or natural selection (survival of the fittest) has any merit whatsoever, would it not be logical to conclude the biological response is to store the most efficient source of energy as fuel to burn during times of want? What say the experts???

9106340a33a2407d63d22e6275300d33

(60)

on August 22, 2012
at 08:51 PM

"The new appetite for meat didn't mean we lost our passion for sweets, though. As Berkeley's Milton points out, the brain's growth may have been facilitated by abundant animal protein, but the brain operates on glucose, the sugar that serves as the major fuel for cellular function. "The brain drinks glucose 24 hours a day," she says. The sugars in fruit and the carbohydrates in edible grains and tubers are particularly good sources of glucose." Read more: http://www.time.com/time/magazine/article/0,9171,994385,00.html#ixzz24JJBTuNS

0b4326a4949718451a8571b82558dc10

(2349)

on August 22, 2012
at 08:00 PM

people went with out carbs all winter...'Times of starvation' is not really starvation and pretty natural.

Bb3d1772b28c02da2426e40dfcb533f5

(5381)

on August 17, 2012
at 09:41 AM

Even monkeys get diabetes from too much sugar, starch and too little activity. Even if you can consider humans fairly well adapted to carbs thats within certain reasonable limits, and in the context of alot of activity. I have yet to see a bakery full of healthy lean people.

81fca18329e68e227cdfef3857bfef96

(1320)

on July 16, 2012
at 02:36 AM

I agree that it is high. I was referencing ACE which is just okay.

96440612cf0fcf366bf5ad8f776fca84

(19473)

on July 15, 2012
at 07:04 PM

I think you've answered your own answer there - "proof" is that the normal state is to have some lean/famine times, esp. in winter, so in those states, we absolutely will burn stored fat. We only need a little bit of glucose for red blood cells and certain types of nerve cells. The rest of the body can use ketones.

96440612cf0fcf366bf5ad8f776fca84

(19473)

on July 15, 2012
at 07:03 PM

Well, glucose from aminos (or muscle cells) as gluconeogenesis for red blood cells and certain types of nerves, and the rest of the body runs off ketones.

96440612cf0fcf366bf5ad8f776fca84

(19473)

on July 15, 2012
at 07:02 PM

I think you've answered your or answer there - "proof" is that the normal state is to have some lean/famine times, esp. in winter, so in those states, we absolutely will burn fat. We only need a little bit of glucose for red blood cells and certain types of nerve cells. The rest of the body can use ketones.

96440612cf0fcf366bf5ad8f776fca84

(19473)

on July 15, 2012
at 06:58 PM

@Bill1102inf: except that it does: http://www.livestrong.com/article/231986-when-does-glucose-convert-to-fat/ - "Glucose is a six-carbon sugar molecule. Your body first converts this molecule into two three-carbon pyruvate molecules through the process of glycolysis and then into acetyl CoA. When your body requires immediate energy, acetyl CoA enters the Citric Acid Cycle creating energy molecules in the form of ATP. When glucose intake exceeds your energy needs.. acetyl CoA begins the process of fatty acid synthesis becoming triglycerides that are stored in the fat tissues of your body."

1c67bc28f4e44bbb8770b86df0463df3

(6719)

on July 15, 2012
at 06:44 PM

25% for men is presposterous, its fat city.

1c67bc28f4e44bbb8770b86df0463df3

(6719)

on July 15, 2012
at 06:43 PM

You train better fasted because your body has a higher amount of CORTISOL (the 'dreaded' stress hormone) circulating. Its a good thing though! Want to see a hot mess? take some cortisol blockers prior to doing anything very heavy. Actually, dont, you would hurt yourself

1c67bc28f4e44bbb8770b86df0463df3

(6719)

on July 15, 2012
at 06:41 PM

Except that the human body barely ever creates fat out of glucose.

Dfe1dfb34939145fe21b3d8fa6832365

(657)

on July 15, 2012
at 05:18 PM

Alcohol is burned even before carbohydrate. Alcohol is most certainly not the bodies most preferred fuel. So that argument that carbohydrate are preferred is kindof moot.

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:23 PM

For women 12-25% for men 5-18%

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:21 PM

25% for men is pretty high.

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:18 PM

Agreed. we are adapted for both, but we tend to lose our ability to use fat unless we let ourselves do it on a regular basis. Also we burn glucose because it is toxic beyond a certain threshold.

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:16 PM

I also train fasted quite well. Yes we burn both, but MOST of our activity can be fueled by fat. You should read Peter Attia's self experiments on high intensity performance over at eatingacademy.com where he measures fat burning at different intensities, and even at 85% of max, he is still burning mostly fat, because he is adapted.

32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on July 15, 2012
at 05:25 AM

The question is then, why do we store unlimited fat, but a small reserve of glucose?

3a9d5dde5212ccd34b860bb6ed07bbef

(1782)

on July 15, 2012
at 04:31 AM

I train well fasted too, but if you're doing high intensity work though I am still burning glucose. Glycolitic activity must use glucose to convert to pyruvate.

2336245491a87ee15d4fb8f8f8283909

(1173)

on July 15, 2012
at 04:29 AM

I fast 18 hours a day and don't like training during the eating window...

2336245491a87ee15d4fb8f8f8283909

(1173)

on July 15, 2012
at 04:28 AM

I'm another one who trains best fasted, regardless of the intensity or duration of the workout.

03a4ec34751186201a56da298ac843ce

(4100)

on July 15, 2012
at 03:47 AM

I was debating this with my doctor who feels that ketosis is only for times of starvation?

Aa5154ef908fc4a5c255c552f32e334e

(256)

on July 15, 2012
at 03:38 AM

Funny.... I am a marathon runner and I train in a fasted state since going paleo!!! I have more energy in a fat burning mode ( fasted, no carb load) than when I train carbed up. This includes sprint work..... I ALWAYS have more energy and can do 4 more sets of hill sprints when i am fasted versus carbed up.

3a9d5dde5212ccd34b860bb6ed07bbef

(1782)

on July 15, 2012
at 03:36 AM

I understand this, but I'm saying that high intensity exercise demands glucose, regardless if you are consuming it from food or not- it will get it. So in that sense, we're all sugar burners too.

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 03:17 AM

Problem is even the most highly trained individual has a very limited capacity for stored glycogen, and except what is stored in the liver, which is only about 100g or less, the rest is muscle specific and can't be shared with any other muscle. Fat doesn't work that way. Even myself with 5% bodyfat has roughly 28,000 kcal in stored energy.

Aa5154ef908fc4a5c255c552f32e334e

(256)

on July 15, 2012
at 02:39 AM

Exactly! This is what I was thinking!

Medium avatar

(10663)

on July 15, 2012
at 02:38 AM

I'm no expert but it makes sense to me!

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9 Answers

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8
5df8b2d60e5e5b95636289eed6e4320d

on July 15, 2012
at 03:19 AM

Really great thought. Most people conclude that carbs (glucose) must be the preferred fuel source, since the body with burn it first. However, when you flip that around, and say that the body is trying to get rid of that fuel (and/or store excess as fat) things become a little more clear.

But, I agree with Alligator, that we are well adapted for the use of both fuels . . . but the proportions should tell us something. Short bursts of high intensity (catching prey, or eluding predators) uses glucose - normal activity (walking, gathering, playing, etc.) uses ketones. Over consumption of carbs shuts down our fat burning machinery (or at least turns it off) - and should be an indication that we are running sub-optimally . . . or as Tommy (Snatch) would say "It's not in sync with evolution."

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:18 PM

Agreed. we are adapted for both, but we tend to lose our ability to use fat unless we let ourselves do it on a regular basis. Also we burn glucose because it is toxic beyond a certain threshold.

Dfe1dfb34939145fe21b3d8fa6832365

(657)

on July 15, 2012
at 05:18 PM

Alcohol is burned even before carbohydrate. Alcohol is most certainly not the bodies most preferred fuel. So that argument that carbohydrate are preferred is kindof moot.

5
3a9d5dde5212ccd34b860bb6ed07bbef

on July 15, 2012
at 03:05 AM

You are only seeing part of the picture. We are all fat burners at low intensities, because i takes more time to break fat down for use. At higher intensities, we are all glucose burners. If you don't consume glucose, then the excess protein in your diet or the protein in your muscles broken down for energy. You see? We are fat burners at low intensities, and sugar burners at high intensities.

Using your same logic, one could just as well say that we store (1200-2000 calories) as glycogen within our muscles and liver..it's proof we're sugar burners!

We burn sugar when it's conducive to X activity, and we burn fat when it's conducive to Y activity. Try burning fat when sprinting. You simply CANNOT. You burn fat after sprinting though.

2336245491a87ee15d4fb8f8f8283909

(1173)

on July 15, 2012
at 04:28 AM

I'm another one who trains best fasted, regardless of the intensity or duration of the workout.

Aa5154ef908fc4a5c255c552f32e334e

(256)

on July 15, 2012
at 03:38 AM

Funny.... I am a marathon runner and I train in a fasted state since going paleo!!! I have more energy in a fat burning mode ( fasted, no carb load) than when I train carbed up. This includes sprint work..... I ALWAYS have more energy and can do 4 more sets of hill sprints when i am fasted versus carbed up.

3a9d5dde5212ccd34b860bb6ed07bbef

(1782)

on July 15, 2012
at 03:36 AM

I understand this, but I'm saying that high intensity exercise demands glucose, regardless if you are consuming it from food or not- it will get it. So in that sense, we're all sugar burners too.

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 03:17 AM

Problem is even the most highly trained individual has a very limited capacity for stored glycogen, and except what is stored in the liver, which is only about 100g or less, the rest is muscle specific and can't be shared with any other muscle. Fat doesn't work that way. Even myself with 5% bodyfat has roughly 28,000 kcal in stored energy.

3a9d5dde5212ccd34b860bb6ed07bbef

(1782)

on July 15, 2012
at 04:31 AM

I train well fasted too, but if you're doing high intensity work though I am still burning glucose. Glycolitic activity must use glucose to convert to pyruvate.

32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on July 15, 2012
at 05:25 AM

The question is then, why do we store unlimited fat, but a small reserve of glucose?

2336245491a87ee15d4fb8f8f8283909

(1173)

on July 15, 2012
at 04:29 AM

I fast 18 hours a day and don't like training during the eating window...

1c67bc28f4e44bbb8770b86df0463df3

(6719)

on July 15, 2012
at 06:43 PM

You train better fasted because your body has a higher amount of CORTISOL (the 'dreaded' stress hormone) circulating. Its a good thing though! Want to see a hot mess? take some cortisol blockers prior to doing anything very heavy. Actually, dont, you would hurt yourself

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:16 PM

I also train fasted quite well. Yes we burn both, but MOST of our activity can be fueled by fat. You should read Peter Attia's self experiments on high intensity performance over at eatingacademy.com where he measures fat burning at different intensities, and even at 85% of max, he is still burning mostly fat, because he is adapted.

4
2336245491a87ee15d4fb8f8f8283909

(1173)

on July 15, 2012
at 04:37 AM

Your body gets the glucose it needs regardless of if you eat carbs or not...amino acids, lactate and glycerol...yep, even from fat.

96440612cf0fcf366bf5ad8f776fca84

(19473)

on July 15, 2012
at 07:03 PM

Well, glucose from aminos (or muscle cells) as gluconeogenesis for red blood cells and certain types of nerves, and the rest of the body runs off ketones.

3
A2c38be4c54c91a15071f82f14cac0b3

(12672)

on July 15, 2012
at 07:53 AM

That is one hypothesis. There are other theories on why we store energy as fat, a common one being that fat is more energy dense than carbs and this means more efficient energy storage.

If you want to evaluate this theory on the basis of species adaptation, look at other animals; it's pretty common for fat to be the basis of energy storage in the body regardless of the macronutrient content of the animal's natural diet. I'm currently not aware of a species that stores excess carbs (or other macros) as huge amounts of glycogen or another carbohydrate storage polymer, though there could be.

Fat could be the preferred energy substrate, but such an observation is not proof. It leads to a hypothesis, which can then be tested. But it's not proof.

2
81fca18329e68e227cdfef3857bfef96

(1320)

on July 15, 2012
at 05:33 AM

1 gram of fat = 9 calories 1 gram of carbs = 4 calories 1 gram of protein = 4 calories

Fat has more energy per gram than the other macros. It makes more sense to store fat as a reserve energy source for this reason. Healthy BF% levels are from 10% to 25% for Men (up to 30% for women). This means a person weighing 150 pounds with 20% BF is carrying approximately 30 pounds of 'dead' weight as energy. To carry the same energy in another macro form would require 67.5 pounds or an additional 37.5 pounds of 'dead' weight. I imagine this would put you at a disadvantage when you are running from a tiger on the serengeti. :)

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:23 PM

For women 12-25% for men 5-18%

1c67bc28f4e44bbb8770b86df0463df3

(6719)

on July 15, 2012
at 06:44 PM

25% for men is presposterous, its fat city.

81fca18329e68e227cdfef3857bfef96

(1320)

on July 16, 2012
at 02:36 AM

I agree that it is high. I was referencing ACE which is just okay.

C45d7e96acd83d3a6f58193dbc140e86

on July 15, 2012
at 02:21 PM

25% for men is pretty high.

2
32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on July 15, 2012
at 02:34 AM

Yup. Also reducing carbohydrates (glucose, fructose, etc) are reactive molecules. They contain aldehydes and ketones that can undesirably react with other biological moieties, such as amines (think: protein/DNA). Fats are not nearly as reactive towards other molecules. So just based on the stability for storage, fats make sense.

Aa5154ef908fc4a5c255c552f32e334e

(256)

on July 15, 2012
at 02:39 AM

Exactly! This is what I was thinking!

1
9106340a33a2407d63d22e6275300d33

(60)

on August 22, 2012
at 08:38 PM

Perhaps stored body fat is merely a reflection of our environment, which does not prove that fat is better than carbs or protein really. We live in an obesogenic environment is all. Sure some say that humans evolved the ability to store more body fat than lean tissue as compared to most animals as a keen survival mechanism. But perhaps our exquisite ability to store body fat easily is more a sign that we must try to remove the abundance of extremely calorie dense foods from our environment, or introduce a lot more daily activity (or both), rather than a sign that we should be dipping our steaks in coconut oil.

Anyway, I thought this was a good read: http://blogs.scientificamerican.com/bering-in-mind/2010/11/02/the-fattest-ape-an-evolutionary-tale-of-human-obesity/

9106340a33a2407d63d22e6275300d33

(60)

on August 22, 2012
at 08:51 PM

"The new appetite for meat didn't mean we lost our passion for sweets, though. As Berkeley's Milton points out, the brain's growth may have been facilitated by abundant animal protein, but the brain operates on glucose, the sugar that serves as the major fuel for cellular function. "The brain drinks glucose 24 hours a day," she says. The sugars in fruit and the carbohydrates in edible grains and tubers are particularly good sources of glucose." Read more: http://www.time.com/time/magazine/article/0,9171,994385,00.html#ixzz24JJBTuNS

1
C00e493393828df34be65ddc25456c7c

(610)

on July 15, 2012
at 07:44 AM

Stored body fat is not proof humans are fat burners. We can just store more energy in fat cells. In these times of plenty there is more likelihood of over-stuffing our fat cells. We were never meant to have such a surplus of energy hanging about.

96440612cf0fcf366bf5ad8f776fca84

(19473)

on July 15, 2012
at 07:04 PM

I think you've answered your own answer there - "proof" is that the normal state is to have some lean/famine times, esp. in winter, so in those states, we absolutely will burn stored fat. We only need a little bit of glucose for red blood cells and certain types of nerve cells. The rest of the body can use ketones.

96440612cf0fcf366bf5ad8f776fca84

(19473)

on July 15, 2012
at 07:02 PM

I think you've answered your or answer there - "proof" is that the normal state is to have some lean/famine times, esp. in winter, so in those states, we absolutely will burn fat. We only need a little bit of glucose for red blood cells and certain types of nerve cells. The rest of the body can use ketones.

0
1edb06ded9ccf098a4517ca4a7a34ebc

on August 22, 2012
at 07:24 PM

Could one not also ask "stored muscle... proof humans are protein burners?" Or, stored glycogen...proof humans are sugar burners?

In men, the only amount of bf you need is enough to protect your internal organs. BF beyond 10% likely contributes to hormonal imbalances like exess estrogen and reduced insulin sensitivity. Having excess body fat would also be a huge disadvantage in the wild.

Also, the reason there seems to be a threshold on how much muscle one can naturally build, in a non-metabolically derranged individual, there is likely also a threshold on how much adiposity one can accumulate (especially given only actually paleo foods). Without activity, the reason one tends to store fat preferential to muscle is because msucle is metabolically expensive to carry.

My point is that all stored body fat really says is that we're able to draw on that as reserve energy, but so are we able to draw on muscle, and glycogen.

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