Does junk food make you lazy?

From Times LIVE: “Does junk food make you lazy?” 

“A diet rich in processed foods and fat – and the extra weight that comes along with it – may actually cause fatigue, a lack of motivation and decreased performance, according to a recent study involving lab rats… excessive consumption of processed and fat-rich foods affects our motivation as well as our overall health.”

(this is categorically false as both diets used in the study being discussed were very low in fat.)

And from Psych Central: “Rat study shows junk food can make you lazy

The theory itself isn’t too far-fetched: a crap diet can cause weight gain and reduced energy expenditure, or a tendency to minimize any kind of physical activity… instead of: “’laziness’ causes obesity.”  And whether or not it’s true, unlike what some would have you believe, this wasn’t the study to prove it.

Food quality and motivation: A refined low-fat diet induces obesity and impairs performance on a progressive ratio schedule of instrumental lever pressing (Blaisdell et al., 2014)

Researchers gave rats ad libitum access to one of two low-fat, high-carbohydrate diets.  One was comprised of processed, semi-purified ingredients – casein (protein), cornstarch and sucrose (carbs), and soybean oil and lard (fat).  It’s a semi-synthetic, sugar-rich highly processed diet.


synthetic diet


The other was chock-full of complex ingredients and rich in fibre:


whole food diet


Both diets had similar added vits and mins, and the images above don’t really reflect the actual diets as they did have roughly similar macronutrient profiles:




And just to clarify, the whole food-based “Chow” is the same diet that is used as the control diet in most rodent studies.

After 6 months, rats fed the synthetic diet gained significantly more weight:


weight gain


Next, the researchers assessed how many times the rats would press a lever to get a sip of sugar water.  In order to speed things up, food intake was restricted to 25 grams per day prior to the experiment to make them hungry <- red flag number 1.

Due to the higher fibre content of the whole food-based diet, it was less calorically dense (3.02 vs. 3.85 kcal/g), so these rats may have been relatively more calorie restricted (ie, hungrier than the synthetic diet-fed rats).

Results: rats fed the synthetic diet appeared less “motivated” to press the lever for a sip of sugar water.  They were heavier, and this is part of what led to the headlines.

The next experiment was admittedly somewhat clever: the diets were switched for 9 days.  However, nothing changed.  That is, rats that got plump on the synthetic, high-sugar diet still didn’t care much for sugar water even though they were given the low-sugar, fibre-rich diet for the past 9 days.  9 days isn’t long enough to impact body weight, and this is the other part of what led to the headlines.




Here’s an alternate interpretation of the results: in experiment 1, the chow-fed rats were hungrier because they were relatively more calorie restricted on the test day (due to the reduced caloric density of the diet, and the fact that both groups were given the same weight of food [25 grams]).

In the follow-up experiment: rats have a difficult time switching from soft chow pellets to hard synthetic pellets.  When they did this, the rats may have been more “motivated” to press the lever because sugar-water calories are much easier than trying to eat the hard synthetic pellets.  And the [heavier] rats who grew up on synthetic food were happy with the more whole food-based, easy-to-eat chow diet, so they didn’t care very much for the sugar-water.


conclusion 1

conclusion 2


I don’t doubt some of these things may have been at play, but this study seems too confounded to say for sure.  The caloric density and texture of the diets weren’t accounted for.

“Our data suggest that diet-induced obesity is a cause, rather than an effect, of laziness.” –Aaron Blaisdell, lead author.  Again, that conclusion may not be wrong, but it’s not the only possible interpretation.

It just seems to me that the awkward food restrictions imposed on the rats prior to the experiments confounded the results.  I’m not too surprised that during the ad lib feeding portion of the study, the synthetic, sugar-fed rats gained more weight.  But 25 grams of chow has fewer calories than 25 grams of synthetic diet, so the chow-fed rats may have been hungrier which gave the appearance of “more motivated;” this has nothing to do with body weight per se (and it wasn’t addressed by the authors).

After reading the media reports, I guess my qualm is more with the researchers and flawed study design than the journalists, who seem to have been quoting Blaisdell pretty accurately.

Non-sequiter… Blaisdell’s Paleo!

From the Latin Post: “Blaisdell, 45, said he changed his diet more than five years ago to eat ‘what our human ancestors ate.’  He indicated he now eats meats, seafood, eggs, vegetables and fruits, while avoiding processed food, bread, pasta, grains and food with added sugar.  As a result, Blaisdell said, he’s experienced dramatic improvements physically and mentally.  ‘I’ve noticed a big improvement in my cognition,’ he said. ‘I’m full of energy throughout the day, and my thoughts are clear and focused.’”


…just my 2 cents on a bollixed rat study.

calories proper

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  • Oliver McManus

    I agree, the 25 grams definitely limits the conclusions that can be drawn from this study. Any reason to suspect the “fast food” pellets are hard and difficult to eat though? Even if they are, their increased calorie density may compensate by making them more palatable.

    • William Lagakos

      I’ve used them before. Hard as rocks! The animals usually need a few days to acclimate.

  • Tuck

    “Non-sequiter… Blaisdell’s Paleo!”

    He’s a little more than just Paleo. He founded the Ancestral Health Symposium (click History at the link):

    • Beth@WeightMaven

      Count me in with the folks who do not want to throw out the Ancestral Health baby with the Paleo bathwater. There are legitimate criticisms of Paleo-the-marketing-machine, but I think Aaron is far more interested in the former than the latter.

      • William Lagakos

        Who’s throwing out “the Paleo bathwater?!” admittedly, I tend to group Paleo & Ancestral together despite cute infographics which show they’re CLEARLY different :)

        (also, I ignore the “marketing-machine,” for peace of mind.)

        • Ash Simmonds

          My problem with the movement is it seemingly overnight went from “steak and tuber – PALEO AS FK YEAH!!”, to “how do I caveman brownie?”.

          • Wenchypoo

            Gotta keep the kiddos’ attention, right? :)

        • Jack Kruse

          Paleo ignores biologic history at your peril. Among the many lessons that emerge from the geologic/biologic record, perhaps the most sobering is that in life, as in the stock market, past performance is no guarantee of future results. Eating the way we did 10,000 years ago to is no guarantee for anything. Context of your thermodynamic issues are way more important than paleo dogma.

          • William Lagakos

            This. “Eating the way we did 10,000 years ago to is no guarantee for anything.”

    • William Lagakos

      Thanks, Tuck!

  • aaron blaisdell

    Thanks for the critique of my study. I agree that there are some confounding factors that need to be resolved for more specific and clearer interpretations. Nevertheless, I still stand by the suggestion that an obesogenic diet either directly, or indirectly through the obesity phenotype it produces, caused the impairment in motivation. Yes, it was possibly problematic to food-restrict the rats prior to measuring their motivation to work for a sugar solution. It is problematic because, as you point out, the equivalent amount of restriction in terms of grams of daily food, may have resulted in different amounts of deprivation in the two diet groups. There are other possible confounding factors that you didn’t mention, such as the fact that the sensitivity to a sweet taste might be different between the two diet groups because the refined pellets were sweet and thus sweet could be less motivating because it is less novel or less tasty, or less rewarding. This was why we conducted a follow-up study that you didn’t mention in which we water restricted both groups of rats (but they were both on free feed of their respective diets) and retested them on the lever-press task with water as the reinforcer. We found the same impairment. Thus, it wasn’t the sweetness per se, but motivation to work for a general class of appetitive rewards (caloric or non-caloric) that are driven by different regulatory systems in the brain, that was impaired. I think the consistency between the results of the water reinforcer and food reinforcer tests shows that a general motivation process, or general fatigue possibly, was impaired, and that the effects of the food reinforcer test were not primarily driven by the other factors you and I mentioned above.

    I would love to hear your (and others’) thoughts on this. And thank you for taking the time to write a critique of the study.


    • William Lagakos

      Hi Aaron, thanks for taking the time to comment.

      “I think the consistency between the results of the water reinforcer and food reinforcer tests shows that a general motivation process, or general fatigue possibly, was impaired, and that the effects of the food reinforcer test were not primarily driven by the other factors you and I mentioned above.”

      That’s a great point about what the water experiment added to your study.

      Regarding the calorie differential, it seems like difficult study to design, nutritionally speaking. If the rats were given an isocaloric amount of the purified diet, then they would be getting less vitamins and minerals as well; another confounder.

      I did consider the differences in sweetness, but thought that may have reflected the “junk food” aspect of the diet (so it was an intentional & meaningful difference between the two diets).

      P.S. I didn’t know you were a founder of AHS. Awesome!

      • aaron blaisdell

        Yes, it’s very difficult, perhaps impossible, to design two diets that are identical in every aspect except for one being made of highly refined/processed ingredients, and the other being made of less refined/closer to whole foods. I knew that going into the study, and received that criticism from many of my own colleagues. But, my point wasn’t to try to equate everything, but to construct two diets that (for a rat at least) reflect the two ends of the spectrum of processing. This replicates the real world case of individuals who consume a lot of junk foods are changing a lot of things compared to individuals eating more whole foods. Once we establish some cognitive and other effects that differ between the two diets, we can then deconstruct what are the main factors that drive the differences. Is it fiber content (i.e., microbiome), key missing nutrients (e.g., ceisine vs. a complete protein), rapidity of assimilation through digestion, etc. etc.? All of these factors, and more, differ between the two diets. This is true of the real world human case, as well, which is to what we want to be relevant. We wanted to start with the holistic approach with high ecological validity before deconstructing via reductionist approaches.

        It was the transformation of my own health after going low-carb primal (I still consume grass-fed/raw dairy), that made me very excited about the Ancestral Health approach. After befriending Brent Pottenger, we thought our contribution to society would be to bring everyone together under a scientific big tent, where there were no gate keepers to the discussion and debate, to investigate and find solutions for the modern world’s challenges to health and wellness.

        And given that I have a rat lab in which I’ve been studying animal cognition for the past 13 years, I thought it would be great to align my new interests in Ancestral Health with my old ones in cognition, and embark on this project. The role of processed foods in health and disease seemed like the logical entry point, given that the big tent Ancestral Health idea is that those are what are the common denominator in human health vs. disease. Rather than high versus low carb or any other idea associated with the paleo diet. The beauty of rat research is that, unlike with humans, I can take a genetically and ontogenetically homogeneous group of rats, assign them randomly to the two dietary conditions, and let the dietary conditions drive any differences we see, unconfouned by healthy user biases, pre-potent tendencies that might lead one individual to eat more junk food and another to eat more whole foods, etc.

        I hope you’ll come to AHS sometime! This year it will be at UC Berkelely (in August), and should be a lot of fun!

        • Ash Simmonds

          See now some of this is why I wish we never actively separated foods into so-called “macronutrients” and then confounded them further by applying a “calorie” value to them.

          I have smart friends who are very health conscious, and mostly follow a whole-foods/ancestral approach – but when headlines about “protein does you cancer brah” and “fat makes you mental” etc etc they STILL raise an eyebrow at my opportunistic carnivore leanings.

          For this latest one from last month it wasn’t until I gave a super basic explanation that the diet these mice were on was basically equivalent to us trying to subsist on powdered egg-whites and cheese covered in McDonald’s deep-fryer oil, with Coke.

          That tends to get a bit of a better reception, even though I know it’s mega simplistic, but when you explain it like that instead of talking casein/methionine/PUFA/glucose/macronutrients it’s easier to get across without glazed eyeballs.

          Until next month when a new “study” hits the headlines… :

          • Chris

            very good point. I also find that many studies do not talk in terms of macronutrient partitioning and that high-fat diets are those 30-50% fat, 30-40% carbs and the rest as proteins…we all know that the health outcomes are on different sides of the border when fat consists of more than 60% from the total caloric count and carbohydrates account for less than 10%

          • William Lagakos

            …and to further complicate things, what about the sources for the macronutrients? …casein & methionine for protein, or a variety? Same question goes for fat, carbohydrate, and *especially* fibre. (cellulose is a pretty poor dietary fibre.)

          • Jack Kruse

            Some of us don’t Ash. Some of us understand what Aaron has really found. Laziness is an electron steal syndrome. When you can not capture the electrons from your foods/environment because the electron receptor is non functional (leptin receptor) then you begin to rob Peter to Pay Paul based upon a bioenergenics steal. Pretty simple to understand when you break food down to what It really is not what scientists think it is by convention.

          • Jack Kruse

            And let me explain this a bit more…………..just knowing something is an electron loss (ie: any AI, neolithic disease, or higher carb diet) is not the key……….it is the rate of loss or change that life pays attention to thermodynamically. When your redox sink is declining you are stealing electrons from all higher energy systems who have them further declining their function. This is why all AI’s have neurologic issues.

            Temperature change offsets electron loss………..the colder preserves it. The warmer depletes it at all scales in the universe and in your cells. It has never been about macronutrients or calories.

        • George

          Very good point about the dietary extremes matching human experience.
          I’m not a rat, but, even so, I wonder if there’s isn’t a better rat food out there.
          The pathogenic mixes remind me of industrial cheesecake formulas.
          But then, there are humans that eat a lot of that stuff.

  • Wenchypoo

    Lazy is a state of mind. That being said, things that CONTRIBUTE to a lazy state of mind are sugars, industrial oils, salt (too much), and foods that break down into them. They also contribute to a body form that’s far less maneuverable, and a metabolism that contributes less usable energy (in favor of storing it away). All these things add up to a visual diagnosis of lazy.

    But then, there are plenty of skinny people riding the couch or hammock–the only difference with them is the stored fat isn’t readily visible, and their bodies are more maneuverable. They’re just as sick inside.

  • George

    I’ll take the n=1 quote from Blaisdell over the study. He’s apparently trying to prove a point he read in Taubes, but it would take ages, needs a talking animal to tell you how it feels about stuff, and is probably epistemologically impossible (or some other big philosophy word) anyway. It was always a good point but may be one impossible of proof.

    • William Lagakos

      It’s a difficult study to design from a nutritional perspective – what do we *really* want to control for?

      that said, I guess this was a good step 1: “paint with broad brush strokes.”

  • Mike T

    A few months ago, I read a study that fed young fit students drinks that either contained equal calories of glucose or fructose and had them wearing accelerometers so they could measure their physical activity and then did a cross over after two weeks. What the were finding is that when the subjects were taking in the fructose, they moved less ate more and had rapid changes to various physical markers. This was not seen on the glucose group and when they crossed over, the findings were replicated. Seems to be evidence to back up the claim that you get lazy and eat too much because you are getting fat rather than the reverse.

    • William Lagakos

      Interesting. Thanks, Mike. I don’t doubt it… it’s somewhat similar, albeit in a roundabout way, to what I was getting at when I said this:

      “The theory itself isn’t too far-fetched: a crap diet can cause weight gain and reduced energy expenditure, or a tendency to minimize any kind of physical activity… instead of: “’laziness’ causes obesity.””

      • Mike T

        I think it was with the same research group in California that Robert Lustig is associated with.

        Also, I really appreciate the effort you put into this blog. Always interesting.

  • Christoph Dollis

    Oh very much, yes.

    Now the studies may have been BS, but eating sugar-rich and nutritionally-deficient foods, perhaps loaded with various genuine toxins without commensurate offsetting good stuff, puts mood and energy in the crapper.