A number of readers have sent me links (thanks, readers) to a new study coming out of the UK that raised some eyebrows all across the Internet earlier this week. The headlines seemed to scream from everywhere “Do High Fat Diets Make Us Stupid and Lazy?” That, in turn, made me scream, so I took a look at this paper in the Federation of American Societies for Experimental Biology: Deterioration of physical performance and cognitive function in rats with short-term high-fat feeding
What I found was a less-than-impressive short-term study on rat performance that told me what I already knew: that it takes a while for new gene expression to really kick in when you radically shift diets. Just like some of you are seeing in the 30-day challenge. So what?
Predictably, this study also prompted the typical editorial “fat kills” reaction from the likes of the New York Times and other bloggers. The ridiculous herd-mentality conclusion reached by almost all of the so-called major media health writers covering this study only serves to solidify my opinion that their heads are so far up their ass-ociation with Conventional Wisdom that they have lost all perspective. In fact, do a Google search for “Do High Fat Diets Make Us Stupid and Lazy” and see how many health publications lifted that sensational headline verbatim. Page and pages. They just took the title from the press release and ran with it.
Here’s what went down. Basically, researchers trained a bunch of rats to memorize a maze in order to receive a sugary treat (the rats, not the researchers…although maybe they got sugary treats, too). Half the rats were also trained to become “proficient in treadmill running” (gotta love that one). Throughout this learning phase, all rats were fed a diet of tasty rat chow that was 7.5% fat, 17.5% protein and 75% carbohydrates. A treadmill runner’s diet if ever there was one.
They then switched half of all the rats from a diet that was 7.5% fat to a diet that was 55% fat (and 29% protein and 16% carbohydrate) and, after giving them four days to acclimate, they tested the high-fat rats against the low-fat rats over the next five days in the maze and on the treadmill and discovered that the high-fat rats were slower negotiating the maze, had memory loss and were less “proficient in treadmill running.” They also found that the muscles of the rats eating the high-fat diet were less able to use oxygen to make the energy needed to exercise, causing their hearts to worker harder – and to increase in size. From this experiment in rat performance, headlines rang out across the world suggesting that high-fat diets make humans “stupid and lazy”. Grok wept.
Of course, the first thing that came to mind for me was, duh, doesn’t everyone know that when you radically shift from a carbohydrate-based diet to a fat-based diet, you can get some pretty wild short-term acclimation issues? The second thought was how stupid and lazy (hey, I’m only using their words) the mainstream media regurgitators are to extrapolate so grossly and irresponsibly from a brief study like this. Maybe I misspoke earlier. Perhaps they had their heads up their assumptions. That’s how public policy starts, folks.
There’s way too much to discuss in depth here, and I suspect a number of my low-carb-blogger pals will weigh in soon (plus we got us a challenge going on here), but a few of my random thoughts regarding holes in the study and questions arising therefrom:
To paraphrase Dr. Michael Eades, rats are not furry little humans and there’s only so far you can go in comparing a 9-day rat study to a human lifetime. This study is a snapshot taken midway through a complex process. I would like to have seen what would have happened if the experiment had continued for a few more weeks. We know that once you shift away from dependence on a very high-carb (high sugar) diet to a low-carb (high fat) diet, you will (at least as a human) experience a number of short-term symptoms or adjustments. Those have been well-documented. Acclimation takes time as new signals from the diet prompt a shift away from glycogen/glucose dependence towards greater fatty acid/ketone reliance. Hormones respond, enzyme systems are increased or decreased, transporter molecules and receptors have to up- or down-regulate. During this acclimation period which may last from two to three weeks, humans will notice loss of memory, fogginess and possibly headaches as the glucose-dependent brain still thinks 100% it’s of energy substrate will be, well, glucose. There will often be a loss of physical energy in general over a period of days as glycogen reserves are gradually depleted while gluconeogenesis ramps up to keep blood glucose stable. Rats probably experience similar discomfort. Of course, once you transition to efficient use of fatty acids as fuel within a few weeks energy, cognition, memory and performance return to normal or improve beyond baseline. Importantly, from the test results it appears that the high fat rats in this study never got into ketosis which might have changed all outcomes (too much carb and protein? The high fat rats were also allowed to consume more than twice the protein grams per day, yet insulin was not measured).
Glycogen depletion promotes short term changes in muscle chemistry and gene expression. This study also looked at UCP3 (Uncoupling Protein3) in the rats’ cardiac and skeletal muscle for signs of inefficient oxidation of energy substrates. No surprise that they found it. Ask your endurance athlete friends what happens to their energy and performance when they switch instantly from a typical high carb diet to a low-carb-high-fat diet. (They don’t know it, but UCP3 up regulates as the body prepares to use more fatty acids.) You’ll discover that they have far less overall energy, that they perform significantly slower and that they run out of steam sooner. They also experience headaches, dizziness and memory loss from the drop in blood sugar. Part of that is because glycogen depletion is a major factor in muscle performance (whether you are on a high- or low carb plan). When muscles are less effective (i.e. when fewer fibers are able to fire due to a drop in glycogen) the heart naturally has to work harder to try to deliver more oxygen to get the chronic cardio work done, hence the enlarged heart in the rats.
But this study didn’t look at muscle or liver glycogen (they said it was too difficult), and only measured blood glucose on the last day of the experiment right after the treadmill run and maze test (RIP, ratons). When they saw equivalent blood glucose levels in high-fat rats, they guessed that liver glycogen had not been depleted and, therefore, was not the cause of the drop in performance. But blood glucose can rise after a workout simply as a result of adrenaline-prompted gluconeogenesis. I forgot to say that these rats got a mild electric shock if they slowed down on the treadmill. Think that might raise adrenaline?
I don’t want to make too much of all this. My point here is that this study only confirms much of what we already know about that midpoint transition in going low-carb. For the media to then extrapolate and say that a high-fat diet makes us stupid and lazy is an insult. Of course, the comment by Dr. Gerald Weissmann, editor-in-chief of the journal doesn’t add to the credibility: “It’s nothing short of a high-fat hangover. A long weekend spent eating hotdogs, French fries, and pizza in Orlando might be a great treat for our taste buds, but they might send our muscles and brains out to lunch.” As my teens used to say, whatever.
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.