A 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, 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!
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.