What Does It Mean to Be Fat-Adapted?
When describing someone that has successfully made the transition to the Primal way of eating I often refer to them as “fat-adapted” or as “fat-burning beasts”. But what exactly does it mean to be “fat-adapted”? How can you tell if you’re fat-adapted or still a “sugar-burner”? I get these and related questions fairly often, so I thought I’d take the time today to attempt to provide some definitions and bring some clarification to all of this. I’ll try to keep today’s post short and sweet, and not too complicated. Hopefully, med students and well-meaning but inquisitive lay family members alike will be able to take something from it.
As I’ve mentioned before, fat-adaptation is the normal, preferred metabolic state of the human animal. It’s nothing special; it’s just how we’re meant to be. That’s actually why we have all this fat on our bodies – turns out it’s a pretty reliable source of energy! To understand what it means to be normal, it’s useful examine what it means to be abnormal. And by that I mean, to understand what being a sugar-dependent person feels like.
A sugar-burner can’t effectively access stored fat for energy. What that means is an inability for skeletal muscle to oxidize fat. Ha, not so bad, right? I mean, you could always just burn glucose for energy. Yeah, as long as you’re walking around with an IV-glucose drip hooked up to your veins. What happens when a sugar-burner goes two, three, four hours without food, or – dare I say it – skips a whole entire meal (without that mythical IV sugar drip)? They get ravenously hungry. Heck, a sugar-burner’s adipose tissue even releases a bunch of fatty acids 4-6 hours after eating and during fasting, because as far as it’s concerned, your muscles should be able to oxidize them (PDF). After all, we evolved to rely on beta oxidation of fat for the bulk of our energy needs. But they can’t, so they don’t, and once the blood sugar is all used up (which happens really quickly), hunger sets in, and the hand reaches for yet another bag of chips.
A sugar-burner can’t even effectively access dietary fat for energy. As a result, more dietary fat is stored than burned. Unfortunately for them, they’re likely to end up gaining lots of body fat. As we know, a low ratio of fat to carbohydrate oxidation is a strong predictor of future weight gain.
A sugar-burner depends on a perpetually-fleeting source of energy. Glucose is nice to burn when you need it, but you can’t really store very much of it on your person (unless you count snacks in pockets, or chipmunkesque cheek-stuffing). Even a 160 pound person who’s visibly lean at 12% body fat still has 19.2 pounds of animal fat on hand for oxidation, while our ability to store glucose as muscle and liver glycogen are limited to about 500 grams (depending on the size of the liver and amount of muscle you’re sporting). You require an exogenous source, and, if you’re unable to effectively beta oxidize fat (as sugar-burners often are), you’d better have some candy on hand.
A sugar-burner will burn through glycogen fairly quickly during exercise. Depending on the nature of the physical activity, glycogen burning could be perfectly desirable and expected, but it’s precious, valuable stuff. If you’re able to power your efforts with fat for as long as possible, that gives you more glycogen – more rocket fuel for later, intenser efforts (like climbing a hill or grabbing that fourth quarter offensive rebound or running from a predator). Sugar-burners waste their glycogen on efforts that fat should be able to power.
Being fat-adapted, then, looks and feels a little bit like the opposite of all that:
A fat-burning beast can effectively burn stored fat for energy throughout the day. If you can handle missing meals and are able to go hours without getting ravenous and cranky (or craving carbs), you’re likely fat-adapted.
A fat-burning beast is able to effectively oxidize dietary fat for energy. If you’re adapted, your post-prandial fat oxidation will be increased, and less dietary fat will be stored in adipose tissue.
A fat-burning beast has plenty of accessible energy on hand, even if he or she is lean. If you’re adapted, the genes associated with lipid metabolism will be upregulated in your skeletal muscles. You will essentially reprogram your body.
A fat-burning beast can rely more on fat for energy during exercise, sparing glycogen for when he or she really needs it. As I’ve discussed before, being able to mobilize and oxidize stored fat during exercise can reduce an athlete’s reliance on glycogen. This is the classic “train low, race high” phenomenon, and it can improve performance, save the glycogen for the truly intense segments of a session, and burn more body fat. If you can handle exercising without having to carb-load, you’re probably fat-adapted. If you can workout effectively in a fasted state, you’re definitely fat-adapted.
Furthermore, a fat-burning beast will be able to burn glucose when necessary and/or available, whereas the opposite cannot be said for a sugar-burner. Ultimately, fat-adaption means metabolic flexibility. It means that a fat-burning beast will be able to handle some carbs along with some fat. A fat-burning beast will be able to empty glycogen stores through intense exercise, refill those stores, burn whatever dietary fat isn’t stored, and then easily access and oxidize the fat that is stored when it’s needed. It’s not that the fat-burning beast can’t burn glucose – because glucose is toxic in the blood, we’ll always preferentially burn it, store it, or otherwise “handle” it – it’s that he doesn’t depend on it. I’d even suggest that true fat-adaptation will allow someone to eat a higher carb meal or day without derailing the train. Once the fat-burning machinery has been established and programmed, you should be able to effortlessly switch between fuel sources as needed.
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. The obese have higher RQs. Diabetics have higher RQs. Nighttime eaters have higher RQs (and lower lipid oxidation). What do these groups all have in common? Lower satiety, insistent hunger, impaired beta-oxidation of fat, increased carb cravings and intake – all hallmarks of the sugar-burner.
It’d be great if you could monitor the efficiency of your mitochondria, including the waste products produced by their ATP manufacturing, perhaps with a really, really powerful microscope, but you’d have to know what you were looking for. And besides, although I like to think our “cellular power plants” resemble the power plant from the Simpsons, I’m pretty sure I’d be disappointed by reality.
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!
A quick note about ketosis:
Fat-adaption does not necessarily mean ketosis. Ketosis is ketosis. Fat-adaption describes the ability to burn both fat directly via beta-oxidation and glucose via glycolysis, while ketosis describes the use of fat-derived ketone bodies by tissues (like parts of the brain) that normally use glucose. A ketogenic diet “tells” your body that no or very little glucose is available in the environment. The result? “Impaired” glucose tolerance and “physiological” insulin resistance, which sound like negatives but are actually necessary to spare what little glucose exists for use in the brain. On the other hand, a well-constructed, lower-carb (but not full-blown ketogenic) Primal way of eating that leads to weight loss generally improves insulin sensitivity.
That’s it for today, folks. Send along any questions or comments that you have. I’d love to hear from you guys.
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Posted By: Mark Sisson
Am not yet totally fat-adapted, still have occasional severe cravings 5 months into this. However when the engine is running ‘fat-adapted-ly’ … Its a joy… No cravings! No afternoon naps (was calling them my ‘post-donut snooze times’!)!!!! Headaches…gone!! Skin rashes….gone!!! Problems going to b’room….gone!! Food tastes extravagant!! 30lbs ….gone!!! I’m seriously clear headed!!! I need to loose 100 more lbs… If its this easy, I don’t care if it takes me another year!!! Love it love it!!!!!
I had stalled with my weight loss while eating very low carb for a while. It was frustrating, and I figured it was just muscle gain, but at the same time it didn’t seem that i was losing fat.
Jimmy Moore recently made a post, here (http://www.marksdailyapple.com/what-does-it-mean-to-be-fat-adapted/#more-30142) about his month long experiment testing and optimizing his state of ketosis. He mentions how some people think of low carb as high protein, but how it is actually more about moderate or adequate protein. I never thought (or maybe completely understood)
how protein can be converted to glucose by the liver, and he claims that about half of all protein you consume is converted to glucose, producing an “anti-ketogenic” effect similar to excess carbs.
Based on how much protein I was eating, I thought that could be why I had stalled for so long. I decided to cut my protein intake down and eat more vegetables in it’s place. It seems to work for me. I have lost weight again and it is definitely fat loss. About 10 pounds in the last 2-3 weeks, after having been stalled or slightly increased weight for 6+ months. Strength is the same. I can also go even longer without feeling hungry. It is a big relief to have found an answer for my stalled weight loss.
I imagine many people on here know all of this already, but Jimmy’s post made it “click” for me, and it sure seems to work. Just wanted to put it out there as I have read comments from people who have stalled and even regained some weight on low carb. Too much protein being converted to glucose could be the issue. I was eating a lot of it myself and it seems like that was the case for me. I encourage anyone to read his post on the subject and post your thoughts. Hope it helps!
Thanks for this. Will try it!
Just so you know, neurons (those things that make up your brain and nervous system) can’t burn fat, and are only capable of obtaining energy from glucose. Food for thought (no pun intended).
Not true, and that can be read about in this post and many other places on the net and in scientific journals. http://www.marksdailyapple.com/how-much-glucose-does-your-brain-really-need/#axzz1zhHzluhA Your brain is happy burning away on ketones with a little glucose to boot, which can be easily formed in the liver.
I meant to say I started eating more FAT and vegetables in my comment above. Sorry.
Hi Keith. I did the same; cut the protein after weight loss stalled. It did the trick and I’m losing weight again. Yay!
Love it Mark, you’ve created another primal term “fat-adapted”
Hi, I started eating primally in mid March this year – have lost 14lbs which might not seem a lot, but this is the only program that has worked for me so far. Previously a lacto-ovo vegetarian for 17 years – have also started eating fish again as I had extreme cravings for it over the last 2 years. Coincidentally,I became crippled with osteo-arthritis in my hips – had to give up dancing/performing and teaching dance (not being physically capable of dancing – for me – really sucks!). Not sure if it’s all the fish and cod liver oil and/or the weight loss, but this week, I’ve been able to ditch my walking stick and am hopeful that I will soon be able to dance again, restart karate classes,go scuba diving and even take a long walk for fun! Other great things; I can easily go all day without a meal/I feel great – knowing that each week I’m losing a steady 1.5 – 2lbs without starving myself/my food bills have gone down ‘cos I’m not buying or eating rubbish,generally eating less!Hardly touch chocolate – just doesn’t do it for me now! My husband is tentatively trying the program as he is so impressed by how easily I’ve lost weight! Next step is to start the Primal Exercises, etc (within my current limitations). Thanks Mark, for your great website!(Thanks also to my sister, who gave me the website details – she too is losing weight which she couldn’t before!)
I’m in my fifties, post-menopausal & insulin resistant – genetically predisposed, I have been told. I fit the profile of a fat burner (no cravings, can go long periods without eating, can exercise on an empty stomach). But I’m still unable to shift the rolls of fat around the middle. I’ve been primal for 12 weeks and no change. What else could be wrong?
Ajay, I have a similar situation. I go by the book, but have been stalled for five years. I’ve been advised to cut my protein intake first, then cut calories, but not below a thousand. I shed sixty pounds and have sixty more to go.
A month ago I was injured and had to stay with my brother and his wife. Theirs is a Weight Watchers household. While I drew the line at grains, I ate basically the same food but just had my eggs cooked with butter. I lost another 9 lbs in 16 days. Now that I’m back on the road and eating primal, I’ve lost another 2 lbs. 11 lbs in June! Part of that loss might have been muscle, but It’s come off my waistline. My poor brother is 5 lbs from goal and crabby and hungry all the time. I can IF for a full day with no hunger and he gets the shakes about every 3 hours. I am a fat burner who can now process variable carbs easily. It doesn’t mean I load every day, but I can eat more carbs occasionnally without destroying my fat burning adaptation.
Cool post. It’s nice to have a little checklist to refer to like that. Even when I ate higher carb, I wasn’t really a beeyatch when I went long periods of time without food — can I give a shoutout to my parents for being fat adapted folks right off the bat?
what a stupid article….if the writers cared about there audience at all or had half a brain, they would point out that changing from primary reliance on carbs to primary reliance of fats is one of the adaptations that the body makes when it becomes accostomed to exercise.
You know, if I was unable to correctly spell ‘their’ and ‘accustomed’, I wouldn’t accuse others of having less than half a brain.
And her name has 3 B’s.
I’ve been going primal for about 5 days now, and I don’t think I’m fat adapted at all. I was STARVING after a meal of steak and vegetables. I have PCOS with insulin resistance. Is it possible that it might take longer for me than some to become a fat burner because of my insulin resistance?
Give it more time. It could take a couple of weeks or more for your body to switch over. Patience, not panic. It will happen.
And if you’re hungry, have a snack! Nuts or fish or some avocado, something filling. I was hungry a lot at first, too. I think this is normal. Eventually, you will adjust and find what works for you.
the article is very misleading, and constructed to sell their particular diet. while i happen to agree that the paleo diet is the healthiest, but biggest point is that your body adapts to being more fate burning when you do regular cardio exercise…the more endurance, the more you rely on fat burning. if these people had graduate dgrees in exercise physiology as i do they would know that…a half truth is a lie. this is a really stupid article by stupid people written to manipulate the audience that reads it. the kind of food you eat plays little role in how fat burning you are.
That doesn’t even make sense… I don’t have a Graduate Degree (so sorry to have an opinion) but if the only fuel available were fat then wouldn’t the beautiful intelligent complex machine that is my body figure out how to burn it???
It seems to me that how you eat would have to effect what kind of fuel you are burning.
debbie-you’re being kind of rude, here. One of the things I like about MDA is the wide variety of responses you get from lots of intelligent folks from around the world. People disagree with Mark and with each other all the time, but it usually seems to be more of a debate /exchange of information rather than argumentative. If you have some insights to share, I would certainly be willing to read them, but please be a little more respectful.
As to selling something, yes, Mark does sell stuff. Both he and the worker bees need money to live on if they’re going to spend time doing this wonderful blog. That being said, this blog is free. Anyone can come here, get the info they need to change their life and never have to shell out a penny. I don’t think you can count this as manipulation.
Lastly, it may not matter to you what kind of food you eat, but it does for me. That’s another thing I like about this site-Mark admits up front that not everything works all the time for everyone, hence the emphasis on journaling and self experimentation. I’ve been through many diets; all had me eating “heart-healthy whole grains” in varying configurations. All failed to keep the weight off. I also had an incredibly hard time resisting cheating. Having gone cold turkey off grains when I started eating primally, I spent a truly miserable week, then my carb cravings went away. I was sick with bronchitis at the time (yeah, I know Mark said to wait until I was feeling healthy before starting the program, but here I was with an unexpected break from work; the timing was just too perfect…), so I can assure you I was NOT doing any cardio, yet I still lost weight. Can’t cardio if you can’t breathe right!
I have, in fact, gained so much energy that I actually Want to exercise, a situation that has never obtained for me on any previous diet I tried. Obviously, since we do not have a 100% obesity rate in this country, some people tolerate carbs better than others. If that’s true for you, then fine-for you. I, however, will probably always need to stay low carb and grain free to continue getting and then remaining healthy.
So please, think what you like, say what works for you, disagree all you want, but please, please, please-stop with the insults. Thank you.
Dude, you misspelled her name. It has 3 B’s.
Yeah, but I was trying to be nice.
As I’ve gotten older and wiser, I don’t pay much attention to whether someone has a PHD, or if an organization has a bunch of PHD’s on it’s staff. Probably half the doctors are spouting B.S. to their patients with chronic illnesses, and I’m convinced that the American Diabetes Asses, and The American Dietetic Asses, are pretty much that…asses.
I also have PCOS, and I think I’m getting there as far as becoming fat adapted. I actually just realized my husband and I IF without even realizing it today, 15 hours. I am really impressed with how it has helped with my high and low energy swings, because they don’t exist anymore! I know that was caused from the insulin resistance. Great post, I was actually looking for a ” checklist” for being day adapted on the website the other day. Now that I have read it I’m excited to know that I’m getting there!
Meant to say fat adapted not day adapted….
I can concur with those having issues with ‘bread’ — my wife and I love the stuff but she is wheat/gluten intolerant so its largely omitted from our diets on that basis alone.
Lucky we aren’t ‘meat’ intolerant
Have you seen Paleo Bread? Made with almond or coconut flour. http://www.paleobread.com/
Is it a problem if I am too keto??
I am definitely fat adapted (3 months primal now, and no 80% rule use as yet) and according to my FitDay tracking I am averaging about 45g of carbs per day. I have been losing 1kg per week on about 1400 calories per day, with no effort at all, IFing regularly with ease and doing fasted workouts often.
Should I be concerned about my carb intake?
Yay, I’m a fat burning beast!
“chipmunkesque”
hehehe love you Mark!
I must be doing something wrong! I find have to eat every couple of hours or I’m starving. I went primal/paleo severals months ago; meat, fish, fruits, veggies, nuts, ton’s ‘o water, lost a few pounds in the beginning then stabilized. 6’1″, 175 – 180lbs, 54 yrs, walk about an hour a day, some yoga, heavy lifts, but food wise, I could eat all the time! Go without a meal? NOOOOOOOO!
What up? Any ideas?
Maybe you’re not eating enough fat to feel satiated.
i second that…it is amazing how long good fat will keep u satisfied:)
Maybe with your height and weight, your activity level demands that you eat more.
I find that my status as a fat burning beast improves over time. Before this diet, I couldn’t exercise without a constant steady stream of incoming food. (So debbbie, you are so wrong you should tear up your worthless master’s degree.) I couldn’t be hungry during exercise without also losing energy. And I was always hungry during exercise.
After I finally got over the carb flu and felt adjusted, my energy quality improved so much. I could exercise fasted and without snacking and lose no energy or strength even when feeling physically hungry. The freedom of that has been amazing.
I still have that freedom now, 11 months since starting the diet, but now that I’m leaner and stronger, I do have to eat a lot more food once more. I don’t have to snack or carb load to keep up my energy level, and I still maintain energy even when hungry. But I do get hungry a lot more now than when I was actively losing weight, and I do have to EAT when I’m hungry.
I wish I could get another 10lbs off me, but I continue to see improvements even without additional weight loss, so I’m happy for now.
Does anyone kn
I wondered if something was wrong with me that I can go without eating for a day before getting hungry. The only discomfort I have from not eating is tolerating peoples reactions. Most are so adverse to this practice I no longer tell anyone when I do or don’t eat.
Does anyone know what effect artificial sweeteners have on fat adaptation, if any? I’m struggling to kick my diet soda habit, and was wondering if that’s part of why I’m not as fat-adapted as I think I should be by this point.
Bingo. Lose the artificial stuff. Every time I felt a craving for sweets I drank several gulps of water and eventually the cravings subsided. Magnesium helps, too.
Check out mercola.com and search on artificial sweeteners. They are truly problematic. Splenda (sucralose) is a kissing cousin to DDT. Lots of folks have reported multiple symptoms, one of which is leaky gut syndrome, worsened by use of these sweeteners.
I don’t remember reading anything on how they affect fat adaptation , but there’s enough bad things to warrant giving them up anyway.
A product you might look into is called “Just Like Sugar”: calcium, Vit. C, orange peel flavorings and ground up chicory root. Tastes like sugar, though I have no idea why with that ingredient list.
Why don’t you make your own soda?
Artificial sweeteners are deadly poisons. Diet Coke is actually worst for your health than regular Coke.
You can make your own SWEET soda without sugar. Stevia is a natural sweetener from the plant stevia (which you can buy in garden centers too). If you buy a sparkling water machine like Sodastream (I have one, it’s awesome) you can make sparkling water. Add a few drops of stevia extract (available at Whole Foods) and lemon juice, voila. You have yourself an all natural sweet soda (lemonade). Added benefit, no waste (no soda can and plastic in the trash).
ok so i tick all the boxes for being fat-adapted-lots of energy, can exercise first thing before eating at all, no cravings, etc etc-I do get hungry 3 hours after breakfast but don’t need carbs in any form-however I haven’t lost any weight after 5 months, yes I’m female and read that others have similar problem despite all the science… so i do fell healthy and admitedly really only 12-15 lbs to lose BUT what’s the deal???
fasted this morning, walked 3 miles with my dog, ate salmon, turkey and primal trail mix for lunch, hiked 3 miles, tri-tip, grilled carrots & bok choy for dinner…fat adapted FEEL AWESOME!
* three hours without eating? CHECK
* skipping a meal an exercise in futility and misery? NOT WITH ME
* enjoy steady, even energy throughout the day? CHECK
* midday naps pleasurable indulgences, rather than necessary staples? CHECK
* exercise without carb-loading? CHECK
* headaches and brain fuzziness passed? CHECK
It is official: I am fat adapted!
I eat once a day. I shop for gorceries while hungry and not pick up unwanted or unneeded food.I don’t work out but I do work a very physically draining job all day without eating. I manage to keep my prediabetic glucose levels within a normal range.
I’m into week 2 of going primal. I’ve had no problem dropping the grains – except when out and I become hungry (I’ve taken to putting a meat muffin in my handbag for thease ocassions). I’ve dropped all sugar except for a tiny amount in my morning coffee without any real dramas also. I have experienced no brain fuzziness or low energy levels yet. Next week I start my final nursing prac (high performance expected) and I’m really concerned about it hitting when I need to have my brain and energy levels working really well. I also don’t feel like eating at 4am when I get up. Do you have any advice on what I could pack in my lunch to combat this if it strikes at work?
fat…eat fat…i like coconut milk mixed with berries very filling…just smash them a bit & let them sit…chill eat…or an avocado or nuts but coconut milk & coconut oil keeps me satisfied for hours a 4am smoothie w/coconut milk & oil would keep u good for a while..:)
After 2 weeks it might not happen at all. Didn’t for me. Eat more salmon or sardines. Awesome brain food
Catherine-I’m an RN, work twelve hour shifts and sometimes I get forced into IF purely due to work load.(Welcome to nursing!) Couple weeks ago, I got floated at three pm to another floor; hadn’t had time to lunch earlier, then got five new patients on the new floor, so never got to take a break there, either. Had breakfast at 0630, nothing but water and green tea all day, then ate my lunch at 8pm after my shift. That was about 4 weeks into eating primally. One of my afternoon patients sent my manager a very nice message about my care of them, so I must have been doing well!
I would guess if you haven’t had the low carb blues by now, you may luck out and avoid them altogether. However, I will tell you that I am faster and much more clearheaded since starting PB. I will be aware that I am hungry and it would be nice to eat, but no longer have the cranky, fuzzy-headed, headachy kind of feeling I used to get.
I do, however, throw some beef or turkey Nick’s Sticks in with my lunch, or some sausage sticks if I can find some without a ton of crap in them. For me, having some fat with my protein if I do snack is vital. With your practical coming up, I wouldn’t even worry about being picky-just get something fatty and high protein to get you through next week, then work on better food sources afterwards. Hard boiled eggs, sausage sticks, beef jerky and macadamia nuts are some of my go-to snacks of choice. There’s also a wonderful product called coconut manna, which is ground up whole coconut, includes the oil; a small tuppertainer with a couple tablespoons of that and some squares of 70%+ chocolate is very Mounds bar-like and is mostly straight fat with a couple grams of sugar.
Good luck with your practicals and welcome to nursing!
“Save one life, you’re a hero. Save a hundred lives, you’re a nurse!”
i must be fat adapted…4 most days i drink coffee with coconut milk & oil & thats it until somewhere between 3 & 5pm & i am not hungry at all. on the 4th i have smoked a turkey/ribs & fixed my family their faves candied baked beans, mac n cheese, corn salad …& brownies…never felt the urge to cheat and they all boo’d me because i forgot the garlic bread…i never even “thought of bread” thats awesome
Sweeeeeet
Great article 
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