Dear Mark: Fat Causes Brain Damage?

It feels good to get back to our regularly scheduled Monday morning programming. “Dear Mark” is a way for me to keep my finger on the pulse of the community, to respond quickly and directly to any issues that may arise. I try to keep abreast of all this stuff, but there’s a lot, and some will inevitably slip through the cracks. When that happens, you guys pick up the slack and keep me honest and informed. These Mondays give me a chance to respond to the things I would have otherwise missed or put off until another time. Thanks for that.

This past week, I received a massive influx of emails from readers worried about the results of a new study. I figured it was a good idea to address it. Here are a few of the messages:

I’m very interested in what your commentary would be in relation to this article. The brain inflammation part is very interesting, but it worries me that this is seemingly being contributed to “high fat” meals. I can’t seem to find more info detailing exactly what the test subjects (in this case rats) were fed. What kind of fat?! In what ratios!? I know from reading your blog to be suspicious of data like this and that the devil is often in the details. In any case this research is intriguing and I wanted to draw your attention to it.




My point of contact is to share a study that just came out from the University of Washington a few days ago.  I know you rarely lack blog topics but this is just ridiculous since we are not told what the high fat diet consisted of.

Thanks again for all of your time and research,




Can you please debunk this article:

Study: Brains show evidence of injury after you eat fat. I’m hoping the rats ate bad food, not just fat, or they ate trans fat.


The study in question comes out of the University of Washington and is entitled “Obesity is associated with hypothalamic injury in mice.” Huh. That doesn’t sound so bad. But then you go and read what the journalists wrote about it and you understand, because they are real fear mongers. “High fat diets cause brain scarring,” out of the mega-obscure Cable News Network, was my personal favorite headline. Not only do you get claims of unequivocal causality with that one, but also promises of permanent brain damage – “brain scarring.”  Scary stuff, for sure. And when a loved one or a coworker or a concerned friend shoves it at you, making smug “I told you so” eyes, it can be frustrating, and it can even make you feel like maybe you’ve got it all wrong regardless of your own success, and maybe you should just give it all up. Media is a powerful force indeed, difficult to completely ignore and laugh off. It works, really really well. That’s why it’s there.

Anyway, I actually found this study interesting and useful. One of the friends of MDA, Dr. Stephan Guyenet of Whole Health Source, was fourth author on it. He collaborated on the research and wrote about it on his blog a few days ago, having foreseen the uproar it might provoke from the Primal/ancestral health community. Stephan sums up the study, essentially telling those crazies among us who aren’t scared of butter and lard to rest easy and avoid jumping to conclusions about the effect of a high-fat diet on the brain, because he and his colleagues certainly were not. They were looking at something very different and far more basic: what happens to the brain as an animal begins to grow obese.

The high-fat diet wasn’t the target; obese mice brains were. This study wasn’t really about the diet. The diet was a means to an end – a way to make the rodents obese so that the effect of obesity on the brain could be studied. It’s well-known that high-fat diets make mice pretty fat, even when they’re relatively low in sugar. (Remember, different species with a different ancestral environment.) So, in order to study obesity, the researchers used the most foolproof obesogenic rodent diet around. As Stephan says, “We choose rodent strains that are susceptible to obesity on purified high-fat diets simply because we’re studying obesity, and we know that feeding this diet to the right strains of rats and mice produces it readily.” The scientists simply wanted to make some mice fat and see what happens to their brains. That’s it. They chose the best diet for doing that to mice, and they even took away their running wheels (mice love Chronic Cardio, actually respond well to it, get chubby without it, and have no real substitutes for it; studies indicate that although mice are enthusiastic about the idea of burpees, rodent anthropometry makes actually performing them impossible) to really make sure it happened. 

This doesn’t tell us a whole lot about humans following and losing fat on a high-fat Primal eating plan. I haven’t heard from or met many, if any, people who got fat eating healthy plants and animals. I’m sure it’s happened, and I’m sure it continues to happen, but the vast majority of obesity stems from refined, high-carb, high-industrial-fat, high-sugar, processed diets paired with chronic stress, bad sleep, and sedentary living. It probably is applicable to lots of “regular” people today, many of whom eat the aforementioned diet that makes them fat and most of whom lead sedentary lives. If that’s the case, they should take note of the study’s (not the journalists’ interpretations of the study’s) findings. Bottom line, if you’re getting fat from the food you eat, this study may be relevant to your situation.

There are a couple more things that deserve mention:

The quality of science reporting, especially with diet studies, is just awful. What the journalists derived from the study was the problem; the study itself was not. In a way, I understand. What’s more likely to catch a lay reader’s eye – “High fat diet injures the brain” or “Obesity associated with hypothalamic inflammation”? Exactly. And technically, the science writers didn’t even really lie. They just seized on the fact that a high-fat diet, typically used to make fat rats, was used to make rats fat. And everyone knows fat makes you fat, and that fat people eat “fatty food” (like chips, pizza, burgers, and sweets, low-carb choices all of ’em). This was just more fuel for the fire.

The quality of the diet was not the greatest, and it doesn’t really resemble what people actually eat beyond the macronutrient ratios. It was highly purified. With these studies, consistency is crucial. You can’t hit up the local farmer’s market for pastured lard, organic corn, evaporated cane sugar, pastured egg yolks and expect it’ll be the same as the lab rat diet of industrial lard, maltodextrin, sucrose, soybean oil, and choline. The former are not always the same, not like the latter food-like substances are alike and identical every single time. This pastured egg yolk will have 1.4 times the choline, 2 times the vitamin A, and half the vitamin E as that one. This slab of lard might be 8% PUFA, while that slab might be 12% and the next might be 17%, depending on what the animal ate. You’d probably end up with healthier rats, but controlled diet studies aren’t interested in that. They need to minimize variability to maximize accuracy, so they opt for purified diets with zero nutrient variation between batches. Two 50 gram chunks of Research Diets D12492 (the popular high-fat rodent diet used in the study) will be identical in every way – but neither will be very identical to your real life diet made of real whole foods.

There’s also the fact that the lard the RD12492 diet (PDF) uses is actually far higher in PUFA than previously reported. Until they had the diet directly analyzed, Research Diets (the company that makes the high-fat rat chow) had been using the USDA database listing for lard to determine the fatty acid composition of RD12492. The new analysis revealed that instead of its fat being 17% PUFA, RD12492’s fat was 32% PUFA. That’s a huge difference. Of course, if you’re eating commercial lard from conventionally-raised pigs, you’re most likely getting more PUFA than Fitday or Cronometer is going to indicate, just like the obese rodents. So keep that in mind when thumbing your nose at this study with Oscar Mayer bacon-slicked thumbs (besides, better bacon is worth it)!

Okay, that’s it for today. I just wanted to clear a few things up for people and prevent wide-spread panic. I hope I succeeded. For a discussion of the actual study, I suggest reading the guy who actually did the thing.

Take care, and thanks for reading!

About the Author

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.

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69 thoughts on “Dear Mark: Fat Causes Brain Damage?”

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  1. Gotta love the media. Create a study, then twist the results to create a media sensation. Are they looking for attention?

    1. Yes they are. And, because of it, millions will continue to believe that all fat is bad. Their health will decline. Many will end up going Primal. Many more, unfortunately, will head down a path of poor health.

      Does anyone care about the health of human beings as a whole outside of the Primal community?!

  2. I hadn’t heard of this report. Thanks for clarifying, though. Just one less thing I have to think about when I do come across this. 🙂

  3. Very nice, I have gotten to the point where I snub reports until I have a chance to look further into them. I blame Gary Taubes for that 🙂

    Mice are enthusiastic about burpees eh? I would love to see that!

    1. yes, I agree, te best line of the whole article has to be “mice are enthusiastic about burpees” That line actually made me snort…out work in my quiet office! LOL… thank you MDA for making my day 🙂

  4. See…this is why I make it a point to never read anything out of Husky territory. Just kidding :). Kind of. Go Cougs.

    1. Hah. Keep waiting for that one. Journalistic integrity has been replaced by the need for sensationalism and the desire to be heard.

      1. Can’t blame ’em, it’s how they make their bread.

        But we all know it’s better to be makin’ bacon 🙂

  5. This just goes to show how much the media manipulate everything by oversimplifying it or just isolating something. Its always possible to turn and twist something to your advantage if you’re facing an audience that won’t ask many questions and that is convinced that fat is bad.

    Great Post!

  6. The news media will always take studies like this one and spin it for greatest effect. Most people will not take the time to actually read a scientific study so they can form their own conclusions. There are often a lot of gray areas to be found in these studies and the results are rarely conclusive. So I do appreciate your taking the time to shed some light on this particular study.

  7. I also commnented on Stephan’s website — This is a perfect example of the disconnect between the way the scientific method works and the way that science is communicated to the media and the public. THe study wanted to look at if and how obesity was associated with changes in the brain. They can’t experiment on humans (because it involves slicing up and examining brains), so they use lab mice. To do the study, they have to make the mice obese. There’s an easy, reliable, fast way to do that (the HFD), so that’s what they do. The result is very interesting, if you are a mouse.

    THe problem is that the media and their audience are interested in humans, not mice, and in the whole diet/obesity/brain spectrum, not just the little bit that’s analyzed here. The disconnect comes when the results are extrapolated far beyond the area where they are, in fact, applicable. This happens all too often.

    I worked for years in the media/press office of a scientific institution. Even if you’re VERY, very careful how you word things in order to avoid misinterpretation, often the media misinterprets the research results anyway. ANd I also know from first-hand experience that many press offices deliberately make things sensationalist in order to attract attention and get the institution’s name in the news. Sometimes the scientists can override this, sometimes they can’t. (it’s not always easy to get a good explanation out of a scientist, either, BTW.)

    Bottom line – go to the source if you find a news item about science interesting, and good luck with the jargon. Use it as an illustration for your kids that learning biology is useful later in life.

  8. Whenever I read media headlines like that and start to doubt myself I just remind myself of the real results I’ve been getting with the primal blueprint. They can say whatever they want.

  9. I understand the rationale for this diet was: because it consistently leads to obesity in these rodents BUT why then conclude that the observed brain changes were as a result of the obesity rather than what they were feeding them?

    The abstract even states “…hypothalamic inflammatory signaling was evident in both rats and mice within 1 to 3 days of [High Fat Diet] onset, prior to substantial weight gain…”

    Yes they see similar changes in MRIs of obese human brains… what are these humans eating?

    I also thank Gary Taubes for my new-found critical approach in regards to published research. I am concerned that in this case: the researchers set out to add evidence to their hypothesis and were not open-minded in their interpretation of the data.

    1. Yes, but the question is: Was that “hypothalamic inflammatory signaling” statistically significant (and to what standard of significance)?

      True, just the observation of such inflammation is intriguing – and might justify further research.

      Given what Mark stated (in the article) about the 32% PUFA of the lard (in the research diet), a study examining the inflammatory effects of lard PUFA might be more relevant to health – especially if the study could be done non-invasively on humans.

  10. This stood out to me: “What the journalists derived from the study was the problem; the study itself was not.”

    I read the news and was hoping you’d comment on this one. Thanks, Mark!

  11. I work as a medical librarian, and I learned to be very wary of MSM reports on medical studies years ago. They’d start screaming about how “nasty substance/behaviour A” “doubles your chance of getting cancer”, or how “current favorite substance/behaviour B” “cuts your risk of cancer by 50%”. You have to read the actual study to find out that the original risk was only 0.1% (or less!) to begin with, so even the “doubles your risk” change was nothing to get hysterical about. But telling the world that their risk of getting a particular disease only goes up 0.1% doesn’t sell ad space, so we get to hear the scary version.

  12. There are two main underlying problems here.

    The first is that the public (and most science journalists as well) does not understand the scientific method, and therefore will misread and/or misinterpret studies such as this.

    The second is more fundamental and, in my opinion, more worrisome. From what I’m reading, the scientists performing the study used the high-fat diet to make the mice obese. What this means, from a scientific standpoint, is that the result (scarring of the brain) can be attributed to EITHER the high-fat diet OR the resultant obesity. Since there were TWO variables introduced (high-fat diet and obesity), one cannot be certain as to which of the two is the cause of the scarring.

    There should have been FOUR groups:
    1) normal, non-obese mice on a non-high-fat diet
    2) normal, non-obese mice on a high-fat diet
    3) obese mice on a non-high-fat diet
    4) obese mice on a high-fat diet.

    Only by separating each combination of variables (2 variables X 2 possible values per variable = 4 total groups) can one properly and validly correlate cause and effect.

    1. Exactly. Any introductory Design of Experiments class would tell you this. To overlook this important point you raise is unbelievable.

    2. That would be the ideal, for sure. But I doubt that it would be possible to get normal, non-obese mice from a high fat diet. If possible, it would probably be difficult and expensive to do. I think the scientists designed the experiment well, especially for an introductory study on the issue. It seems based on what Mark wrote that the scientists made it pretty clear what was actually studied, but that the media put their anti-fat spin on it.

      1. Well designed or not, and media-spin or not: it is at least potentially misleading for the researchers to conclude what they have concluded — based on their chosen methodology and reported observations. There are other interpretations which an open-mind would explore… such as: were the observed brain changes as a result of the obesity or what they were feeding them?

        In my opinion, the researchers went in with a preconception and saw just what they wanted to see… much as the media folks tend to do.

      2. Actually, it is. MSG makes rats fat, and incidentally has long been known to cause lesions in the hypothalamus (in rats) which impairs the rats’ appetite (in the sense that they just keep eating).

  13. I’m curious as to when this will end. When most of the world will realize that real fat (animal fat, coconut, avocado, nuts, etc.) is NOT harmful. It does not make you fat. It does not lead to brain damage. It is essential.

    Will it be in my lifetime? That would be sweet. I’m 23 so I think it’s possible.

    1. The irony also is, why do we continue to fatten cattle up in feedlots, knowing that fat will make us sick?
      See what I did there?

      1. Hmmmmmm….good point. Going to share this, as a matter of fact.

  14. When will the media finally take responsibility for the influence that they have on people? I know that we are not lifeless slates that soak up and believe everything that the media feeds us, but it plays an undeniable huge role in the way that we think about things. The media simply plays upon whatever will grasp people’s attention and keep them interested. Maybe if they weren’t so concerned with this they could give us useful information that we could ultimately use to improve our lives.

    Personally, when I embraced a high fat diet my depression disappeared and so did the fog that had encapsulated my brain!

    1. Media is controlled by government…..government is controlled by greed!!!!! Media will never take responsibility!

  15. Actually, the study says this “Here we report that unlike inflammation in peripheral tissues, which develops as a consequence of obesity, hypothalamic inflammatory signaling was evident in both rats and mice within 1 to 3 days of HFD onset, prior to substantial weight gain. ”

    Doesn’t mean the same applies to humans of course. Mice are not designed to eat high fat!

    1. This is something that bothers me in a lot of these diet related studies. Especially the ones that find negative correlations with eating fat and meat. They turn out to be studying mice, an animal that is mostly an herbivore in nature, and lives on mostly grains and fruit.

      Clearly, if I wanted to know what diet makes a cow healthy, I wouldn’t go make studies on a cat!!

  16. DID someone say BACON!?!?>>>>>

    here we have another of the carefully crafted “JOURNALISTIC MISLEADING INCOMPLETE VIEWS”……Its like they think the same as the TV producers..”GEE…IF WE PRINT IT OR TELL THEM THESE THINGS ON TV>>>IT MUST BE TRUE>>>RIGHT???”>>>
    OH MY POOR BRAIN>>>>>Time to get some fat/meat/and gelatin stuff…Whos got the head cheese and Liver sausage??????

  17. Everyone take a deep breath and remember: those conducting the study and those reporting on it are not one in the same. Now, choose the target of your ire wisely.

  18. Hi everyone,
    I enjoyed reading this while drinking my plunger coffee laced with cream: yum. 🙂

  19. Ok, so ive been thinking about fat lately (in foods, haha). Greek yoghurt has become incredibly popular the last few years, credited as being healthy due to its content of good fats, but then I’m confused how fat-free greek yoghurt is also credited as healthy… Isn’t the point gone then? Or is it still healthy? I am skeptic to fat-free/low/reduced but also full-fat, and confused about what to chose.

    1. maybe i’m wrong,but i thought greek yogurt was the darling of CW because of all the protein…and the fact you can get it fat -free. now, we here at mark’s site know the fat’s important as well.

  20. I posted this same article on my blog, and had the following questions right away:

    1. Doesn’t the brain NEED fat?

    2. What kind of fat specifically?

    3. What does this have to do with ingestion and subsequent storage of starches converted to fat?

    4. Does this study have anything to do with THIS one? (Then posted a link to WAPF’s rat fat study)

    Then I recalled another article I posted about how as much as 2/3 of the medical research reported in this country CANNOT BE REPLICATED, and is therefore in error or faked completely. Yep, publishing for publishing’s sake!

  21. I was complaining the other day about a headline on CNN that read “Belly fat linked to Dementia in Women”. But when you read the study, it talks about the hormone adiponectin which is higher in LEAN women, which has actually been linked to dementia – not belly fat.

    If I want to learn about something, I feel like I have to do my own research.

  22. It is far more likely that I have suffered severe brain scarring from watching the media, and especially during an election year.

    1. yeah, watching the ron paul run by the media can do the same thing.

  23. The Mainstream Media, like the government, simply cannot be trusted. Trusting a reporter is the same as trusting a politician.

  24. Ohh!
    Makes sense.
    I feel like I’ve read so many of these studies before….what you always have to stress is the KIND of fat being taken in. The studies always either omit that fact or deny that the fact they are shoving down their test subject’s throats IS IN FACT UNNATURAL.

  25. Phew! Now that I understand the whole story it makes much more sense. The media sometimes only tell a small portion of the tale and it can be very misleading. Thanks for clearing this one up mark!!

  26. Mark, once you’ve mentioned Stephan Guyenet as a coauthor, you might address his food satisfaction hypothesis. It seems to go sharp against what we seem to know/believe about the role of insulin.

  27. Excellent description of how it feels sometimes wading through the tide of ignorance and lack of critical thinking.

    God bless you Mark, you’re a wonderful human being.

  28. I think all of us collectively worry about our health a little too much…like we are going to live forever. Isn’t there a quote that says one thing is for sure..none of us are going to get out of this alive. We should enjoy the food we have in its most natural state and work with it if it works with our bodies.

  29. The “high fat” rodent diet that produced the rats’ obesity was also loaded with sugars — the equivalent of more than a dozen Coca Colas per day for an American on a 2500 kcal./d. diet — as well as unhealthy soybean oil. In fact, the “high fat” diet looks an awful lot like the SAD with its sugar and PUFAs.

    1. Yes, after reading the .pdf file on the rodent diet that Mark supplied, I came to the same conclusion.

      Moreover, scarring of the hypothalamus can lead to effects relevant to other aspects of Primal lifestyle besides eating behavior. The hypothalamus is involved in hormonal control of sleep, stress, and much more:


  31. I have a question that I hope somebody can help me wrap my head around. My aunt struggles with body weight — although she is only about a size 10, her sisters are very petite — and tries to eat the CW version of healthy, with 1% milk, etc. She places no value on quality of food, purchasing most of her groceries at Wal-Mart, and also eats fast food regularly, although carefully choosing “healthier” options on the menu. She is currently preparing to undergo surgery to remove her gallbladder, and is also having problems with her liver (even being a teetotaller) and pancreas, requiring hospitalization over the holiday. In order to “minimize severe inflammation” in her system, her doctor has placed her on a ZERO fat diet for the last month. (I react strongly to gluten, and suggested to her she might get tested for celiac or other food allergies as an inflammation culprit, but she won’t.) This doesn’t sit well with my understanding of health. Under what circumstance is a zero fat diet good for you for any length of time? Thanks in advance for all replies and opinions — don’t worry about offering medical advice, she’ll never take it! I’m asking to satisfy my own interest 🙂


    1. I wish I could, Papa Grok! I love your approach to it. I’m pretty concerned for my aunt, who’s not quite to the stage where she “should” be having “diseases of age,” but she’s one of those people who accepts medical authority pretty much without question (says the doctor said fat would increase inflammation), and refuses to even ask him whether removing wheat from her diet would help, because she’s afraid he’d say yes and “the cure is worse than the disease.” Gak!

      I think it would be great to go find out what the heck that doctor’s at, but unfortunately it’s not my body and I can’t, so I was hoping someone might have some information I missed. It all seems like nonsense to me!

      1. Gall bladder issues are a huge red flag for celiac/ gluten issues. I think you’re exactly right about your aunt needing to be strictly gluten free. Robb Wolf has talked about this extensively on his podcast. It amazes me that most people would rather undergo surgery than try something as benign as excluding wheat from their diets. There is a very good chance that your aunt may not need surgery if she gives up gluten. I hope she feels better!

        1. Thanks for Papa Grok and Sabrina’s comments! My family has never been able to wrap their heads around my husband’s inability to drink milk (the bunch of dairy farmers, them), so explaining grains as a “food allergy” didn’t make sense to them when I/we went Primal. But I’ve had lots of success describing it as like “wheat diabetes,” since they eat a SAD and of course have a number of diabetic friends (correlation, hmm?). My aunt has scheduled her surgery for March 16 and insists on going through with it, but I have convinced her and my grandmother that they should talk to their doctors about getting tested for celiac and/or cutting gluten grains, at least, from their diets. (Since both of them hate rice, that really only leaves corn and potatoes.) It’s a start!

  33. Trying to do squats, but my knees are crunching, cracking and hurting to the point of only being able to do 3. This happened when I was doing Cross-fit as well. Stopped the squats and the knees became better. Should I continue through the pain or am I doing permanent damage?

    1. Many people can live and be strong and not do squats….I firmly believe that life can go on…without doing an exercise that hurts you…Damage done can be strengthened again…but damage really never goes away like magic.
      Ease in on it…if it wont go..then don’t force it…Squats are NOT for everyone>>>

  34. Thanks Mark for this. My mom waved the articale about how “high fat diet causes brain damage” She’s reading the Primal Blueprint book right now and was worried. Now I can calm her fears!

  35. Today Well has some Minnesotans who specifically look at a high fat diet. The abstract doesn’t mention rat body composition or the kinds of fat used, just that exercise reverses the damage.