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Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...

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January 06, 2009

Low Carb Diets Affect Short Term Memory

By Mark Sisson
43 Comments

ConfusionA soon-to-be published study in Appetite [2009 Feb;52(1):96-103] (but apparently already published online earlier this summer) done by a group at Tufts seems to have “proven” that when you remove carbohydrates for three weeks from the diet of people who have depended on them for decades, you get some short-term memory loss, fuzzy thinking and/or mood swings. In what appears to me to be yet another colossal waste of time and money, the Tufts researchers concluded that “the brain needs glucose for energy, and diets low in carbohydrates can be detrimental to learning, memory and thinking.” What? They got grant money for this? Most of my Primal Blueprint 30-day challengers could have told you that for free! If you understand the power of gene expression and the ability of the human body to acclimate, this study only “proves” what we’ve known for over 100 years.

Here’s the gist: the researchers gave memory, mood and “cognition” tests weekly to two groups of women who were dieting over a period of three weeks. Nine women were on a “low-carb” program where they could eat all they wanted of fat and protein-based foods (we say “ad libitum”), but zero carbs the first week and less than 16 grams/day for the remainder. The other 10 women were on a reduced calorie, balanced diet recommended by the American Dietetic Association with plenty of carbs. The results: women on the low carb diet “performed worse on memory-based tasks than ADA dieters… These impairments were ameliorated after reintroduction of carbohydrates.” You can view the complete abstract here.

And based on this they suggest that low-carbs diets aren’t all they’re cracked up to be. Another Tufts/ADA anti-low-carb conspiracy?

There are so many problems with this study I don’t know where to begin. I guess I’ll start with the most glaring issue, since it renders moot almost all the others. The length of the study was only three weeks. If you are a reader of MDA, if you have read Michael Eades, Modern Forager, TheIFLife, Jimmy Moore and any number of “low-carb” blogs, you’ll know that three weeks is about the average acclimation period to any low-carb diet. And at less than 20 grams a day, this was a true low-carb/ketogenic diet. During that three week period, when you cut carbs so dramatically from previously levels, your memory and cognition will likely get fuzzy, your mood will swing and your energy levels will drop. This is normal and to be expected when cells that have been programmed for decades to burn primarily glucose are now being deprived of this main fuel. It’s especially true of the brain. But as we discuss here so often, life is about gene expression and the signals your send those genes. When you deprive a sugar-burning human of his/her carbs and replace those calories with fat and protein, your genes get the signal to start up-regulating fat metabolism and ketone production.  After three weeks, the acclimation (we call it “keto-adaptation”) is usually complete and brain cells start to thrive on a mix of ketones and the small amount of glucose produced in the liver via gluconeogenesis in the complete absence of carbohydrates. In fact, much of the brain prefers ketones to glucose when you are in ketosis. It’s a beautiful thing. Energy overall increases, mood stabilizes, you think more clearly, that regular three-hour hunger for carbs disappears, you burn of fat stores, you can skip meals with no noticeable effects, etc. Had the researchers followed their subjects for a few more weeks they would surely have seen all this. In fact, Lt. Frederick Schwatka wrote about it in the New York Herald in 1880 when describing an expedition with the Inuit: “When first thrown wholly upon a diet of reindeer meat, it seems inadequate to properly nourish the system, and there is an apparent weakness and inability to perform severe exertive fatiguing journeys. But this soon passes away in the course of two or three weeks.” He thrived for two years on that diet. So did Stefansson in 1929.

Other issues I have with the study are the small sample size (less than 20 subjects), the fact that subjects “self-selected” their diets and the fact that little was made about the four-pound average weight loss among both groups, especially since the low-carb group could eat all they wanted of non-carb foods. To me that’s huge…but the researchers had an agenda: “the results suggest that weight-loss diet regimens differentially impact cognitive behavior.” Whatever.

Now, having said all this, remember that the Primal Blueprint “maintenance” level of carbs is between 100 and 150 a day (depending on your age, size, gender, etc). That’s not a ketogenic diet – it simply lowers insulin and forces the body to look for extra energy from fat stores so you don’t gain more fat. Even the PB “sweet spot of weight loss” allows 50-100 grams a day, barely dancing in a range of ketosis and nothing like the <16 grams in this study. But for those of you who wish to maximize fat loss for a while and go “full-ketosis” just keep in mind this all-important three-week window of keto-adaptation, where you may not want to take your SATs or go on Jeopardy for the first three weeks. But after that? Who wants to be a millionaire!

Further Reading:

How to Guide: Making the Switch to Primal Living in 6 Easy Steps

The Context of Calories

Have you Decided to Healthy?

TAGS:  mental health

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43 Comments on "Low Carb Diets Affect Short Term Memory"

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Son of Grok
7 years 8 months ago

I was just thinking about whether or not I experienced fuzziness or memory loss when I first started going PB. But I can’t remember 😉

Way to attack this one pro-actively Mark!

The SoG

Holly
Holly
7 years 8 months ago

I so appreciate your honest and upfrontness Mark. I’m with SoG, I don’t remember any memory loss or fuzziness. And while SoG meant it as a pun, I’ll say in all seriousness, it clearly wasn’t significant enough to be noted.

Broseph
Broseph
7 years 8 months ago

That’s funny, because this study says quite the opposite! Sugar leads to memory decline, not meat!

Jane
Jane
7 years 8 months ago

I wouldn’t think ZERO carbs for the first week could be considered healthy. Even Atkins lets you have like 20 or something.

Joe
Joe
7 years 8 months ago

I experienced some mood swings for about a week. My wife (and I) just figured that was because I was being a pain about not eating dessert anymore.

primalman
primalman
7 years 8 months ago

On the positive side, I think that this study helps support the idea of making small changes slowly over time. Many people will feel slow if they drop carbs to nearly zero over night and I don’t recommend it. I drive on the same roads as these people :).

Earth Beauty
7 years 8 months ago

I have tried to tell others that eating every three hours is malarkey!!

RedBeerd
RedBeerd
7 years 8 months ago

I believe I saw this one before, and if I recall correctly the low-carb group experienced a larger “drop” in cognition, but still scored higher overall than the low-cal group.

chris
7 years 8 months ago
Before people can discuss this intelligently their first needs to be consensus on what “low carb” means. I have a text book in front of me that refers to the Zone as a low carb diet (the Zone recommends 40% of calories come from carbs, the “food pyramid” recommends 45-60%). While I hardly consider the zone low carb, it does serve to illustrate how the definitions of the term are all over the map. So is low carb 40% of total calories, under 100g a day, under 16, etc..? I think it should be painfully obvious that super low carb… Read more »
Keenan
7 years 8 months ago
Chris, “low carb” is a relative term. Ask an Atkins adherent and they’d tell you that 0-20 is low. I wouldn’t say 40% is low at all, but it is low relative to the suggested government diet. I don’t know why super low carb diets are unhealthy for any reason. Fruit and vegetables don’t seem to be required, perhaps just useful. Check out Hyperlipid (http://high-fat-nutrition.blogspot.com/) to see what I mean. There doesn’t seem to be any benefit to staying in deep Ketosis (unless you’re fighting off cancer, maybe) but some people thrive on it. That being said, the weight training… Read more »
Mark Sisson
7 years 8 months ago

Keenan, well said. And I might add that once you are able to play in the 100-150 range every day, dropping to 40-60 or 60-80 on an IF day or a keto day is a no-brainer. It’s when people go from 250 or 350 grams a day to 50 that they experience the transition blues. And dig that 300 grams carbs a day is still on the low end among those who eat 2500 calories and get 60% of it from carbs as our USDA would suggest. (60% of 2500 is 1500 calories and at 4/gram, that’s 375!)

Dana
Dana
7 years 8 months ago
Jane’s remark about it being unhealthy to go without carbs is a common thing I hear but I’m becoming less and less convinced that it’s true. We are *able* to eat carb foods to some extent, but it isn’t strictly necessary and we don’t even make all the enzymes needed to process that stuff. We do make some amylase (starch-digesting enzyme), but not a lot of it. Glucose source: Carbs are not needed for this. As you’ve stated even in this post, we can make glucose from other things. I read someplace that about half the protein we eat above… Read more »
Dana
Dana
7 years 8 months ago

“And the Inuit did it up until very recently and the Maasai sometimes do it now.”

Go without plant food, I mean. Obviously the Maasai are not snowed in anywhere. 🙂 🙂 🙂

pat
pat
7 years 8 months ago

I am on Kimkins and I never had headaches from cutting carbs. Must not have noticed it.

JE Gonzalez
7 years 8 months ago
“Fiber: If you eat enough fat it greases the skids, so to speak. Or that has been my experience. If you don’t use it all for fuel, don’t need it all for hormones and cell-building, and you don’t have your insulin up to pack it away into storage, where else is it going to go?” I have had the very same experience, although I get more than enough fiber from vegetables. As for phytonutrients I think they should not be avoided if they give us so much benefit. We certainly do not need plants, but they sure do add a… Read more »
Andrew R - Go Healthy Go Fit
7 years 8 months ago

I’d fund a study that stated “Low carb diets get you jacked abs!” Is there anything like that coming out? Hahaha, but yes Mark I agree, the three week period is borderline conspiracy and 100% negligent for those people out there looking for real answers. Well done sir, keep fighting the good fight.

All the Best,

Andrew R

Ruth
7 years 8 months ago
Mark, Thank you for writing this. I started Atkins after being a frustrated near-vegan (I ate seafood, but no dairy, and no other meat) for a year. Before that, I ate meat, but no dairy, and many years ago, I was a complete vegetarian for a couple of years (but did eat dairy). OK, my point: The first day on Atkins I felt great (the momentum, I guess). The 2nd and 3rd day, not so great. I couldn’t sleep because I kept getting up to pee 20 bazillion times a night. Cutting carbs makes you shed a ton of water… Read more »
Ken
Ken
6 years 13 days ago
Hi Ruth, I’ve been reading through all the comments on Mark’s site (and I’d like Mark to chime in as well) and your’s struck me a little odd. As an endurance runner, hydration is at the forefront of my daily routine. It is because proper hydration is key to proper cell function. Dehydration is not a healthy or pptimal state to be in. For one, it makes your blood less viscous which adds stress on your heart. But what I wanted to point out is, how do you know what is the right amount of water retention? Or that the… Read more »
Steve
Steve
7 years 8 months ago
I definitely noticed the “fuzziness”. But I’ll add some perspective here. I went low carb (< 20gr) for a healthy lifestyle with weight loss as the most immediate result desired. I lost 125 pounds in 7.5 months. The first three weeks were tough. I had headaches, I was a bit surly, and I had to concentrate a little more to complete my work. I would compare it to having a few mild flu symptoms. But look at the upside of working through that! I lost 125 pounds, got off numerous medications, I look much better, my confidence is higher, I’m… Read more »
gkadar
gkadar
7 years 8 months ago
Where does red wine fit in all this? Is ethanol considered a carb or a fat? I know that the body metabolizes it like a fat, but????? Most days I consume close to zero carbs (except what’s in a glass of milk and an apple, tomato, red pepper,…. blah blah etc. no bread. no cookies. no pasta. no rice.) but, hey, what about my beautiful half bottle of dry red Australian wine? Do I have to forgo my reward for getting home alive? I was thinking recently since I’ve been taking Harp Seal Oil capsules (seem to have a better… Read more »
Kelly the Kitchen Kop
7 years 8 months ago

Well, I just started low-carb yesterday, so I’ll know soon if it gives me “fuzzy brain”. My plan is to make this a lifestyle now, not just a short term “diet”. I’d like to lose 10# or so, then just stay away from sugar and grains – how much healthier I’d be! Problem is, I need more good ideas to keep me on track (“what the heck can I eat?!”), so I did this blog carnival, I hope people will share their favorite ideas or recipes!

http://kellythekitchenkop.com/2009/01/healthy-low-carb-meal-ideas-our-first-real-food-wednesday-blog-carnival.html

markus
markus
7 years 8 months ago

i experienced lower endurance on atkins on my 7 mile runs initially – this was cured but upping the fat – what may also be happening is that those beginning very low carb do not compensate enough with fat… we still unconsiously cenosr our fat intake – years of anti fat conditioning

i agree that there is an adapive period – but i suspect people are still not eating enough fat – and possibly too much protien.. we should, on a ketogenic diet at least, be eating more fat than protien

m

Mark Sisson
7 years 8 months ago
Markus, you are correct. People still shy away from dietary fat when they are trying to lose stored body fat. It’s a tough thing to learn because it’s counterintuitive, especially in light of 30 years of being told fat is bad. AS for running on Atkins or PB, I’m not sure you could race well on ketones (since there’s no way to store them) but you can certainly find a “sweet spot” where you run easily and have plenty of fats/ketones to handle that load. I have some athletes (people who, against my better advice, still want to run/cycle/swim hard… Read more »
Sue
Sue
7 years 8 months ago

“I am on Kimkins and I never had headaches from cutting carbs. Must not have noticed it.”

That’s surprising. Is Kimkins still advising low carb, low calorie and low fat all together? I thought that place shut down?

Son of Grok
7 years 8 months ago

Sue,
Agreed. i was under the impression that Kimkims was universally deemed insane and unhealthy and kicked to the curb. I don’t know enough about it.. but kimkims was the “diet” where you only ate like 500 calories per day right?

The SoG

Sue
Sue
7 years 8 months ago

That’s right. Also, if you’re going to do low carb it should be high fat not low fat and low calorie as in Kimkins.

trackback

[…] may remember the misguided buzz about low carb diets affecting short term memory, but what about high sugar diets affecting long term […]

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7 years 8 months ago

[…] may remember the misguided buzz about low carb diets affecting short term memory, but what about high sugar diets affecting long term […]

trackback

[…] matters: low/no-carb diets are NOT long-term brain busters (I can attest that getting started sucks, and the second time is worse), training environment, the […]

Dr Dan
7 years 8 months ago

Of course we will also be getting greater amounts of omega 3 on a paleo/primal diet and therefore this should counteract any memory loss from the first few weeks of non-carbs.

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[…] What Was I Just Saying About Ketosis? […]

Trinkwasser
Trinkwasser
7 years 8 months ago
I had somewhat of the opposite response, when I started low carbing it was because I had finally discovered I was right on the cusp between diabetes, impaired glucose tolerance and reactive hypoglycemia, and a lot of the mental fuzziness and physical energy drops I’d been experiencing most of my life cleared up. Also my depression symptoms stayed under control on 1/6 of the medication and my ADD symptoms became almost non-existent By testing http://www.alt-support-diabetes.org/NewlyDiagnosed.htm I discovered that on the Healthy High Carb Low Fat diet my BG was shunting back and forth several times a day from the 150… Read more »
wes
wes
7 years 8 months ago

Wondering if coconut oil can help with the transition? There’s been research that it produces ketones and has quick results for alzheimer patients. Maybe it can help lift the fog? Plus it’s all fat.

trackback

[…] traps, there are indeed a few temporary physical effects to expect in the transition. Check out my take on the latest “study” suggesting that low-carb living compromises you cognitively. […]

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[…] Compare to 080905 Post time to comments One of the topics that came up frequently during our last Paleo Challenge was the pain of the first couple of weeks. Common complaints were loss of energy, loss of focus, and overall tiredness. Mark at MDA fights off some bad press related to the loss of memory during the first two weeks after switching from a carbohydrate-based diet to a fat-based diet. Keep in mind that the original study was a duration of 9 days on lab rats. Take it with a grain of salt – unless, of course you are… Read more »
stuart poole
stuart poole
6 years 4 months ago

Fuzzy head, mood swings, sleepy, this is part of the transition when you start to come of high carb diet.
Had them all. 18 months later 75lbs lighter, cant remember the last time I had a cold, Best condition Ive been in for years.
The study is short term b— crap.
Keep rocking Mark.

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[…] Sisson describes and discusses Ketosis here and here. Read these posts…and feel free to email me any questions you may […]

Nicola
Nicola
6 years 1 month ago

The brain fog does pass. I drank eleuthero tea (siberian ginseng, not the same as regular ginseng). It is a herbal remedy for memory improvement and it really helped.
My job depends on me doing mental arithmetic all day and I do it fine with low to no carbs, it is just a transition phase you go through.

Jim
Jim
5 years 10 months ago

I would suppose that a short term study of those quitting smoking (or any addiction such as carbs) would have similar results, and likewise conclude that the brain needs nicotine for optimal learning, memory and thinking.

Chris
Chris
5 years 9 months ago
I definitely experienced the “carb flu”, but I also cut my carb intake by a lot initially. I wouldn’t say my mind was fuzzy – it was more having big energy level swings. I would feel very tired at times in the middle of the day, and had some head aches. I experienced that on and off for about 2-3 weeks, but after that my energy kicked into over-drive! I’ve felt great ever since, went from 185 to 170 lbs and still feeling fantastic. The results of that study are only negative because it only lasted for 3 weeks. The… Read more »
Nikki
Nikki
5 years 9 months ago
I used to leave no carb unturned but I always had really low energy and had a foggy feeling quite often. Last week I went low carb, and my energy levels soared and there was no brain fog.I also noticed my energy levels felt smooth and stable, I could go hours without eating and I didn’t feel hungry. But every morning I woke up feeling with my arms and legs feeling so shaky and weak. I had all of this energy but my body felt physically sick. I wound up eating a couple of buckwheat pancakes and that made a… Read more »
Lisaloo
Lisaloo
1 year 11 months ago

I am on week 6. I eat up to 50 grams of carbs and no more everyday, often less. Fat at 60%, Protein at 25%. I had a rough couple of weeks, then I was cruising and lost 5.5 lbs. I upped my energy output lifting weights, and now my cheeks are red and I am tired and I feel like I am comin down with a cold or flu. Is this the start of Ketosis?

trackback

[…] Low Carb Diets Affect Short Term Memory | Mark’s Daily Apple – Chris, “low carb” is a relative term. Ask an Atkins adherent and they’d tell you that 0-20 is low. I wouldn’t say 40% is low at all, but it is low relative to … […]

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