fuel- fat v. sugar

Answered on September 12, 2014
Created September 12, 2012 at 5:33 PM

I've been eating primal for the last several months, and I have no idea how to tell if I'm a "fat burning beast" or still just using sugars as fuel. Here's what my diet looked like today (I've already planned my dinner, so I've included that info in the stats): Calories: 1823 Fat: 105 Protein: 122 Carbohydrate: 75 (38 of which are from sugars) This is a pretty typical day for me. Other important info: I'm a 145 pound, 32 year old female, 5'7". I lift heavy stuff 3 x week and run and/or play tennis one other day. I've lost about seven pounds and one dress size since I started eating primal, and I feel fucking great.

So, my questions are: 1. How can you tell if you are burning fat for fuel? 2. If you don't FEEL different when burning fat for fuel, can you accurately guess, based on gender/activity/diet about when this happens? 3. Am I consuming too much much sugar/carbs for my body to switch to burning fat?

Thanks in advance. I feel like the more I learn about nutrition, the more I realize I don't know, well, anything.



on September 12, 2012
at 05:34 PM

Sorry- the formatting on my nutrition info was lost when this posted. I hope it still makes sense.

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6 Answers


on September 14, 2012
at 07:51 PM

I belatedly found the answer to my own question:

There???s really no ???fat-adaptation home test kit.??? I suppose you could test your respiratory quotient, which is the ratio of carbon dioxide you produce to oxygen you consume. An RQ of 1+ indicates full glucose-burning; an RQ of 0.7 indicates full fat-burning. Somewhere around 0.8 would probably mean you???re fairly well fat-adapted, while something closer to 1 probably means you???re closer to a sugar-burner...

No, there???s no test to take, no simple thing to measure, no one number to track, no lab to order from your doctor. To find out if you???re fat-adapted, the most effective way is to ask yourself a few basic questions:

Can you go three hours without eating? Is skipping a meal an exercise in futility and misery? Do you enjoy steady, even energy throughout the day? Are midday naps pleasurable indulgences, rather than necessary staples? Can you exercise without carb-loading? Have the headaches and brain fuzziness passed?

Yes? Then you???re probably fat-adapted. Welcome to normal human metabolism!

From http://www.marksdailyapple.com/what-does-it-mean-to-be-fat-adapted/#axzz26SMCjz9y


on September 12, 2012
at 05:39 PM

The only way I know of to check for sure is to measure your blood glucose and blood ketone levels. If your blood glucose is ~100 in a fasted state and your ketone levels are above 1 your undoubtedly a fat burner. However this method is rather expensive. (FYI, i have never felt the need to do this test on myself)

Here are some other ways to check: Lower your carb intake to ~20g per day, if you feel just as energetic, your a fat burner. Skip a meal, or two in a row. If you fell just as energetic, your a fat burner. Go for a LONG run or play session, if you never "Hit the wall" or "Bonk" or have a "second wind" your a fat burner.

From your use of the phrase "Fat burning beast" i guess you read Mark's Daily Apple. According to Mark, at 75g of carbs, you should be fat burning.



on September 28, 2012
at 11:06 PM

I don't agree that "everyone is different". When it comes to glucose, everyone is the same in that your brain needs about 100-120g a day to function properly.

If you consume between 0 to 120g of carbohydrates, some of that energy requirement will be met by gluconeogenesis, and the rest from ketones.

If you consume 120g or more of carbohydrates, then your brain will selfishly use the first 120g, and any extra will be stored in your muscles and liver.

Since you are eating 120g of carbs, I very much doubt that you are in ketosis, so I doubt that you are "a fat burning beast", although of course everyone burns fat for aerobic exercise.



on September 28, 2012
at 10:33 PM

With carbs that low if you weren't burning fat effectively you'd be really tired and sluggish.

Easy test... eat something like 2 cream lattes (Heavy) and say 1 small chicken breast for a day. No carb, very limited protein. If you feel fine you are accessing fat stores well. If you feel Hangry or really exhausted you could be better.


on September 12, 2012
at 06:59 PM

You do not feel hungry when you are a fat burner - but it can take a long time to get there. You do not get moody, you do not get headaches. If you are a sugar burner those things happens with about 4 or 5 hours of nothing to eat.



on September 12, 2012
at 06:21 PM

It probably varies from person to person, but here's how I know I'm in that sweet spot of running on fat:

(BUT...before I oversimplify, I should say that we are always running on both fat and carbohydrate, even on a lower carb plan. But most people here know what we mean when we say "fat adapted" or "running on fat" -- when the vast majority of your activity is fueled by fat - not just when you're exercising, but all your body's activity - breathing, blinking, sitting upright, cooking dinner, typing on PH...)

Like a previous poster said, you can tell for sure that you're burning fat if you test for ketones in your urine, but you can also be fat adapted and not show measurable ketones that way.

When I'm running well on fat:

I can go hours and hours without feeling hungry. And when I do feel hungry again, it's true, genuine hunger and not me feeling "hangry" - the combination of hungry & angry, where your blood sugar is low and you feel like you're gonna murder someone or possibly eat your own arm off if you don't get fed in 30 seconds, know what I mean? ;-) No irritability, no misdirected anger. And I don't have cravings for any junk when I get hungry. I honestly want real food - chicken, steak, fish, vegetables, cheese (I do dairy). I can walk past a cake, pan of brownies, or whatever, and not think twice about it. Not tempted in the slightest.

I'm bursting with energy both physically and mentally. My head is super-clear, very sharp thinking, and maybe this is just personal to me, but I tend to feel more even-keeled, optimistic, and ambitious when I'm on a good fat-burning jag. I am a major pessimist and it sometimes takes an act of Congress to get me to accomplish things, so when I'm feeling good and getting things done that's a sign, too.

Now if only I could get back there! Haven't been doing too well lately.. :(

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