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Sunday, April 13, 2014

Oh Rats!! II: Usefulness of Rat Studies & Unmotivated Fat Rats

An important result was that motivation to lever press was impairednot only in food-restricted rats working for food reinforcement (sucrose), but also in water-restricted rats working for water reinforcement.  The non-specificity of the impairment suggests that the REF diet affected general mechanisms of motivation rather than those specific to the feeding behavioral system. Taken together, these findings lend support to the hypothesis raised by scientists [28,29] and journalists [30] that obesity may not be the result of impaired motivation (lethargy).  Rather, an obesogenic diet, such as that consisting of highly processed, refined foods, may induce obesity and disrupt motivational mechanisms of the central nervous system.  This hypothesis awaits further empirical scrutiny and does not necessarily rule out the lack of will power as a contributing factor to obesity.
Three guesses who/what reference 30 is, and the first two don't count.  Oh my.

image link
In Oh Rats!! I, I discussed some rat research on sugar addiction (so-called).  A major player in this area in the peer review literature is Dr. Nicole Avena who has taken the leap to mass-media diet guru -- and I mean guru in the worst sense of the word.  Avena is a bit different from many of the fellow gurus, when she goes on TV and such, she has an impressive bio and research background following her, so I'm going to hold her to a higher standard.  There are two problems with her book, the first being the definitiveness with which she places blame on sugar and by extension carbs, to the exclusion of fat and/or the sugar/fat combination.  This is unquestionably in conflict with her own research findings.  The second being that she characterizes rats as "very good models of humans because we have similar brain systems and neural circuitry."   This implies that research in rats is easily translated and applicable to humans.  

Now, I've worked with rats quite a bit in my former career ... was reminiscing on Facebook about that yesterday, actually.  They are very good for some things, but not for others, and neurobiology being a tricky one.  I worked mostly with antidepressants at the discovery level. At that time new drugs went through our company something like:  organic chemist makes a bunch of candidate chemicals → "tox 1" does in vitro tests for carcinogenicity, etc. → "tox 2" rodents acute toxicity / "efficacy 1" (forget the department name, looked to see if bound neurotransmitters and such in vitro) → metabolism (me, also developed the assays to quantify) / toxicology / "efficacy 2" → development and eventually human trials.  A lot of my work was done in cooperation with other departments and I honestly don't recall how many candidates I worked on that never made it past that.  There were times when I had a study planned on Monday only to walk into work and learn that at the meeting on Friday the powers that be had nixed that candidate due to some finding, somewhere.   Many drugs would show promise in some initial tests and it wouldn't pan out.  I also worked on drugs later down the chain that were in human clinical trials.  Well ... guess what?  None got that far if they didn't work on rats, yet many a promising drug in rats didn't work so well in humans and was relegated forever to the dust bin.

So the other day I was reminded of my experiences from my former career while watching a morning news program talking about this report in the LA Times:  Processed foods mess with rats' motivation, study suggests.  Of course the TV report came off more like "the real reason obese people are lazy is that the refined food diet that made them fat also makes them lack motivation" ... but ...   In any case, the report ended with the anchorlady cautioning that this was a rat study, but then reading the last line of the article:
Rats are a great animal model for humans because there is so much overlap in the systems that regulate appetite and metabolism.
WOW!!! That's good to know!!  This would not be my observation in terms of feeding behavior that I observed.   It's pretty fair to say that rats housed in cages with ad libitum access to pellets -- that resemble those compressed saw dust fuel pellets for stoves and furnaces, though I'm told the high fat chow we never used resembles cookie dough -- really aren't such great approximators for human behavior after all.   Solid chows are almost all homogenous pellets.  Every time they eat, they are consuming the perfect macro ratios of their designated purified complete nutrition formulated RatZone diet.  They can't skip the corn and wheat and go straight for the lard or fishmeal or vice versa.  No ... every single bite they take, likely their entire post-weaning life ... consists of the exact same "food".  Further, rats will eat at random intervals pretty much throughout the day, and night, though certainly more over the course of the active phase in their circadian cycle.  

They get essentially zero water from this chow and therefore drink quite a lot of it.  Our cat used to do this as well when we fed him dry food.  Since switching him to canned I almost never observe him drinking water and I only have to change it to keep it fresh and clean.  Thus since you can't tell an animal to overconsume something, the best way to get them to consume a lot of sugar is to put it in their drinking water.  And apparently the way you get them to consume a lot all at once is to offer the food intermittently.  A rat in the wild that is hungry acts all addicted you know -- scurrying all about in search of sustinence!  A rat in a cage surely recognizes its confinement and at some level knows its survival depends on that stuff when its provided.  

Rats are not housed in the equivalent of even a studio apartment in Japan, let alone a two story home.  Their food is put there, they don't have to go get it, even if that only means a trip to the fridge. Ours looked like this one, though they were for relatively short term "housing" and our purposes were different.  Still, rats in cages in no way mimic any human condition, even prison!   Rats don't eat structured meals and they didn't appear to like to eat in groups.  There would often be one rat chowing down while the others lay curled up together in a corner.  As Avena states, the rat is free from environmental pressures, cues, and lets throw in body image or whether someone has an outfit that fits for an upcoming occasion or even to wear to work. 

So for all the aforementioned reasons, and probably quite a few others, I think it's fair to say that in terms of nutritional and behavioral studies, rats are far from "very good" or "great" models for humans.   This does not mean rat studies are useless, often for the very same reasons!  For example, if you give a rat ad libitum access to food and water, it will eat and drink solely for physiological reasons.  Thus we can tease out some of the psychological reasons for certain behaviors from the physiological ones.  Rats don't eat because they've been told breakfast is the most important meal of the day, or never to skip a meal, etc.  They also don't get to drink the KoolAid in any sense, they get plain water unless someone's trying to get them hooked on evil white stuff and then they get sugar in water, no flavors.  This tells us a LOT about the individual foods or components thereof.   Not everything, because the native diet of a rat and a human and how we process macros is different, but quite a bit.  Because we really can focus quite a bit on individual types of fats, proteins and carbs, forms, combinations, etc.etc.   To me the king rat study of them all in this regard was that CAF rat study.  Because give them human junk foods and out the window goes their interest in any boring diet pellets and nom nom nom (some more than others) and obese they get.  Due to their physiological reaction to the unique foods in combination, and not the components thereof.  There is nothing, not even the disapproving look from a momma rat, to stop them and they just keep on eating.

We ALL need to keep this pretty close to the fronts of our minds whenever rat nutritional and behavioral studies come along.

So back to what got me on this in the first place -- that TV report.  The basic gist was that not only is junk food making us all fat and sick, but it's also apparently making us a bunch of unmotivated lazy fatties as well.  When I tracked down the article, something else caught my eye:  the lead researcher and source of the quote was none other than Ancestral Health Society co-founder Aaron Blaisdell.  I've had a few conversations with Aaron back when I frequented PaleoHacks.  Let's just say he's a pretty avid Taubesian Low Carber who, obviously, has an interest in the whole paleo/ancestral health scene.  I read the article, and then I tracked down the study, Food quality and motivation: A refined low-fat diet induces obesity and impairs performance on a progressive ratio schedule of instrumental lever pressing in rats.

I gotta say, I'm quite disappointed in the study design.  Forget about the motivation tests and all that, but if rat studies are good for anything in nutritional contexts, they are good for controlling intake and "compliance".  There's no under-reporting or over-reporting.  There's no cheating.  There's no "who knew that was high fat or carb or whatever".  There's just rats eating and drinking the same dang thing morning, noon and night.  High level of control there from a compliance point of view.  There's NO excuse for careless lack of experimental control from a cofounding variable point of view.  But perhaps the reason this was lacking in this study was hinted at in the Highlights:
  • High fat diets (HFDs) cause obesity and cognitive impairment in rodents.
  • HFDs are also highly refined obscuring the causal factors in their effects.
  • We fed rats a refined or unrefined low-fat diet (LFD).
  • The refined LFD induced significant weight gain and motivational impairment.
  • Therefore, diet quality, not fat, is a cause of obesity and cognitive impairment.
So to test their hypothesis, "Rats were allowed ad libitum access to unrefined rodent chow (CON Lab Diets 5001) or a purified low-fat diet (REF, Research Diets D12450B) for 6 months, and body weight and performance on an instrumental lever pressing task were recorded.".  Let's look at the diets they used, shall we?  Although the diets are described in both the LAT and journal articles as being of roughly the same protein and carbohydrate content, they are not.  Furthermore, in addition to differences in the macro ratios, the types of protein and fats differed between the diets.  WHY?  There are a ton of rodent diets out there.  Surely they could match two better than what they did.

  • The unrefined diet also contained 42.5% more protein than the refined diet.  This is huge in any sort of nutritional comparison study.  I listed all possible sources from the ingredients list, but your major sources are likely the fish and pork meals and whey protein.  This differs dramatically from the casein used in the refined diet.  The protein in neither diet would be "natural" for a weaned rat ... ever seen a rat catch a fish or take down a pig?
  • The refined diet contained 20% more carbohydrate than the unrefined diet.  This is also pretty significant.  It's also fair to say that describing "meals" and "ground" grains as unrefined is a bit misleading.   Perhaps uber-highly refined would have been a better term for the study diet.
  • The fat content is 35% higher for the unrefined diet but at such low levels likely not that much of a factor.  However the fatty acid profile of soybean oil differs from that of lard.  Since the fat type is always a huge issue in those so minded (as one presumes Blaisdell would be), this quality differential is a big deal.
In any case, they fed the rats these two diets for ad libitum for 6 months and the weights are shown at right.  The means appear to be 334g and 398g.  This is a considerable difference, especially with the axis scaling used, but to put it in perspective, the REF rats only weigh about 20% more than the CON rats. 

Before going on, I was curious how this compared to the high-sugar low fat rats in the CAF rat study. It looks like (although number designations differ), this is the same diet used as the refined diet in Blaisdell's study. Oops, I see I should have put the alfalfa meal as a protein source instead of carbs. Not going to bother changing that.

After 15 weeks the LFD (corresponding to Blaisdell's REF) rats averaged about 320g vs. 260g for the SC rats -- an increase of about 15%.  Meanwhile, rats given the choice of a variety of human junk foods favored the fatty ones resulting in a diet that was equivalent in fat percentage to the high fat diet but that was consumed in considerable excess.  The two low fat diets were consumed to identical caloric intake at ~690 cal/wk, while the HFD fed rats consumed only ~80% of LFD calories (~560), but the CAF rats consumed around 900 cal/wk which was almost 30% more.  The CAF rat ending weight varied from about 340 to 575g, and an average about 460 grams.  Thus the CAF rats weighed over 75% more than the standard chow rats!!  

I would note that the differentials in protein content are even larger between the low fat diets in this study as the standard chow is 34% protein.  The weight gain differentials vs. caloric intakes are likely due to the efficiency of calorie storage in these rats, where roughly 15% of calories in protein is swapped for carbs between the two low fat chows.  The average 15 week weight for HFD about about 350g which is most likely due to the efficiency of converting dietary fat to body fat.  I would also note that the HFD diet had 17% sucrose so it contained fat + sugar and yet, even those rats did not overeat.   Blaisdell's study was  six months, and the difference in weight gain could be attributable to the aforementioned differences in digestion and fat conversion efficiencies and time.  

Back in Blaisdell's rats, and I'll excerpt from the LAT article:
"The obese rats really showed impaired motivation," said Aaron Blaisdell, ... "It is as if the rat is thinking 'This is too much work.'"
This is based on the following protocol where:
One at a time, the rats were moved to a new environment where they were taught to press a lever to access a small spoonful of sugar water.

Once the rats had learned the behavior, the scientists made it successively more difficult for the rats to get the sugar water. The first time it took just one push of the lever to get the sugar water, the next time it took three pushes, then six pushes, and so on. In another, similar experiment the number of times the rat had to hit the lever went from one to five to 10 and so on.
Both sets of rats eventually grew tired of the task -- sometimes taking long breaks between lever pushes, and sometimes giving up completely. But the researchers found the obese rats took significantly longer breaks between pushes and gave up on the task twice as fast as the svelte, healthy rats.
"The biggest break a lean rat took was about 5 minutes during a 30-minute session," said Blaisdell. "In obese rats the breaks were much longer -- about 10 minutes for the longest breaks."
From this we are to extrapolate all manner of things about how motivated people are that are overweight to obese and the dietary cause of their apparent lack of motivation?  Now the following IS interesting:
To see if the obese rats were simply less impressed by the sugar water because of the refined sugar in their diet, the researchers ran the experiment again, this time restricting the rats' water so they were thirsty by the time they came into the test environment. This time, a lever push was rewarded with plain water. The results, however, remained the same.
So ... the rats eating the refined food diet, those rats that were "forced" to consume a diet of 35% sugar ... those rats DIDN'T go nuts for the sugar water like a bunch of addicts on a bender?  Having sugar in their diet might make them less sensitized to it?  I wonder what Avena would have to say about this line of thinking!  In any case, it didn't matter as the heavier rats showed less interest in plain water too.  So the overweight rats were less motivated to drink than the lean ones.  There could be another explanation for this besides cognitive impairment.  I'm on the edge of my seat to learn of future studies to find out.  Not. 

From the journal article:
The REF diet, despite closely matching the macronutrient ratio of the CON diet [not], differed in the nature of those macronutrients. In particular, the refining process breaks down complex foods into their simple constituents that are more easily absorbed through the intestines and assimilated into the body. This may be one of the major factors for why junk foods are so addictive and obesogenic. Notably, the REF diet consisted largely of simple sugars and refined flour. The CON diet, on the other hand, contained more whey, soy, vegetables, fish meal, and complex carbohydrates. Refining into the simple constituents also can affect the flavor profile, texture, and other featurecof the food to change its palatability and reward value.
The weight gain, as with the CAF rat study, is likely explained by calorie efficiency (and no, that doesn't debunk CICO) differential between carb and protein.  The CON diet was highly refined as well.  I mean whey?  Vegetables?  Alfalfa meal is listed as a protein source and then there's beet pulp.  All of the grains were milled and the meats "mealed".  Still, I'm more concerned with this characterization of the REF diet:
While the REF diet serves as a model for a human junk food diet, more research is needed to investigate which of the many factors that differ between the two diets have the greatest impact on behavior and cognition.
How about finding a REF diet that mimics a real human junk food diet?  There's probably a low protein high fat diet out there that will have sucrose in it as well (as most do).  Neither the LFD or HFD from the CAF rat study resemble any sort of human diet.  Junk food is not a mixture of corn starch, sugar, casein and some soybean oil and/or lard mixed together at varying proportions.  Interestingly, one doesn't need to go to extremes with fat in the diet to produce fatter rats.  It is not unusual for obese humans to report eating upwards of 40% fat diets when intake is verified.   Even a 15% sucrose diet, for an obese human consuming 3000 calories a day amounts to over 100 grams or over a half cup of sugar.  The 35% sucrose diet?  That's well over 250 grams or over a cup and a quarter of the evil white stuff.  Not every obese person is shoveling down Little Debbies by the box full and washing them down with liters of Coke.

I would note that the non-fattening CON diet, in addition to being quite high in protein, included "refined grains" that are supposedly obesigenic according to the paleos and Dr. Avena's sugar equivalency index.  Wheat Belly would surely protest if the rats had gotten fat on that diet.  I'm surprised Grain Brain hasn't tried to spin this with "just imagine how much more addle brained the obese rats would have appeared had we fed the CON group Kerrygold and prime rib!

In any case, neither diet comes close to mimicking human diets in the Western world where 20% is considered very low fat and 30% is a target for reduced fat intake.  Nope -- a fat percentage with a 1 in front is not applicable to the "real world" these researchers purport to be studying.  

Now I find it hard to believe that either Blaisdell or Avena has never come across the work of Sampey (lead author) or studies feeding rats diets that really mimic a human junk food diet.  Apparently both are so biased by their favoritism towards low carb diets and blinded by the dopamine and sugar-lit reward centers to view their experimental evidence in the context of other studies.  And yet it is the work of researchers like Blaisdell and Avena from which we get the all-but-accepted-as-fact scientific evidence-based wisdom that sugar is addictive and this is the real cause of the obesity epidemic.  It is stated with definitive zeal, not with conscientious caution as a scientist would.  Because, as it turns out, despite myriad obvious reasons to qualify their statements, they both feel that rats and humans are similar enough in the brain wiring to make rats a very good to great model for human behavior.  

From LAT:
Anecdotally, Blaisdell said the two groups of rats seemed to have the same energy level -- so it's not that the obese rats had grown more lethargic overall than the thin rats. Instead, he thinks it is possible that the refined diet is changing the chemistry inside these rats' brains. 
"A colleague of mine has found that if you impair the dopamine system in rats, they give up on harder tasks much sooner than rats that had not had an impairment," he said. "Diets that induce obesity are likely deregulating that dopamine system."
But wouldn't you know the LAT changed their article title since I started this post?  It's now:  Junk food makes you lazy: Study looks at overweight, unmotivated rats.  Only Blaisdell said it did not appear to.  

Blaisdell said he still has more work to do to confirm that thesis. For example, down the road, he might run this experiment again, and then euthanize the two groups of rats and compare how many dopamine receptors they have in their brains.
In the meantime, Blaisdell said, it is not such a stretch to say that what is true for rats may be true for humans as well.
image URL
OK ... the next time you need a drink and are willing to walk to the fridge for it before your heavier friend is motivated to do so, remember this study.  Now ... I highlighted in red there because just before I got ready to publish this up, I was looking for something and came across a different link to this study.  Thank you Whole9 Hartwigs!   New study shows how junk food diets prompt laziness.   Now ... like I said ... this could be a bit of poetic license/lost in translation stuff going on, and scientists need to be more careful/proactive in my opinion in how they word their responses at official press releases and all that.  I'm willing to give some leeway ... it can't be easy.  But then I read this:
They conducted their study in rats, whose physiological systems are very similar to those of humans. ...
... The first group ate a normal rat's diet of unprocessed foods - such as ground corn and fish meal ...
Seriously ... am I the only one that doesn't see the oxymoronic nature of this?
... Lead researcher Aaron Blaisdell says their findings suggest that lethargy may arise from consuming a junk food diet....
That's not what Blaisdell said to the LAT, but this is specifically attributed to him and if he even implied it, he's overstepped bounds here.  Physical activity wasn't even evaluated so he should have kept mum on that altogether.  But inasmuch as he shared an impression that it wasn't a problem to one media outlet, he should be consistent!  Incidentally, food intake, not even for one week, was not measured either.  It sounds like they stuck some rats in cages, had some poor grad student look in on them, change their food, water and bedding, and let them be for 6 months.  Then they did some experiments for a day or two in about 2 weeks time and then off with their heads!   So now thanks to Blaisdell's either sloppy or deliberately misleading communication skills, we have *lethargy* in the reports for this rat study.  And ... we are reminded that humans are a lot like rats!  Yes ... some are.    

So lack of motivation on a singular drinking task has now morphed into lethargy, but  it's about to get even worse, and I'll leave the original formatting from this excerpt intact.

'Long-term diet patterns contribute to cognitive impairments'

Pub food
Long-term consumption of junk food - highly processed food that is high in sugar - contributes to not only obesity but also cognitive impairment.
Interestingly, the investigators switched the two groups' diets after 6 months. This time, the obese rats were fed the more nutritious diet for 9 days, while the lean rats were fed the processed junk food diet.
Despite eating the more nutritious diet, the obese rats' weight did not improve, nor did their responses to the lever task. Additionally, when the lean rats ate junk food for 9 days, their weight did not noticeably increase, and their responses to the lever task did not become impaired.
This result suggests that a long-term pattern of eating junk food - not short-term changes - is to blame for obesity and cognitive impairments, the researchers say.

SAY WHAT?  So now we have gone from lacking motivation to do some task to get water to lethargy to cognitive impairment?    I know that what they observed in the rats could technically be cognitive impairment, but y'all know what you're thinking when you hear that term.  Junk food makes you stupid ... and fat ... implication: fat and stupid.  Of course this might well be explained by the fact that the rats are unlikely to gain or lose much weight in 9 days after 180 or so days on their previous diet.  And perhaps there may be something about carrying some extra weight and/or hydration level that motivates a rat to press a lever for some water (with or without sugar).  Remember ... eventually ALL rats gave up so it couldn't have been that urgent.  

But Blaisdell was not done yet!  Oh no!!

So overweight people are lazy according to Blaisdell, that's a given.  His data just says we should blame the diet (food manufacturers?) ... because, after all, humans are just like rats.  So we don't want to draw too many conclusions, but he's going to go on anyway. 

Blaisdell is STILL not done, however.  In a section entitled "Poor diet linked to chronic diseases", 
Because the study was performed in rats - which have similar physiological systems to humans - the team believes their findings will apply to humans.
Yes, we got that from the beginning of the article.  I know ... just in case we have been eating junk food and might not remember.  Alongside a text box highlighting all the things wrong in the world that we could attribute to a cupcake, we're told:
Another finding from the study shows that the rats on the junk food diet had a large number of tumors in their bodies by the end of the study, whereas those on the nutritious diet had fewer, smaller tumors.
I have the full text of the study.  There is no mention of tumor assessment.  Did they dissect the rats and quantify the number, size and type of tumor in them?    Did they dissect all of them?  Or how many?  And scroll up to the last red highlight in this post.  IF they did dissect ANY of them, why didn't they analyze dopamine receptors in the brain?  That would have made sense given the hypothesis they were purportedly testing.  The utter irresponsibility of this information is staggering, but sadly not surprising.  Because this is, in the end, about the ancestral health background and biases of Aaron Blaisdell.  
"We are living in an environment with sedentary lifestyles, poor-quality diet and highly processed foods that is very different from the one we are adapted to through human evolution," Blaisdell says. "It is that difference that leads to many of the chronic diseases that we see today, such as obesity and diabetes."
If only we took a cue from our close evolutionary friends, the rat, and switched to a diet rich in ground whole grains, high in fish and pork protein meals, augmented with whey and alfalfa, and topped with but a wee teaspoon of lard.  A NUTRITIOUS DIET.  Just don't tell Grain Brain Perlmutter when you reach for your kombucha or NorCal margarita faster than some person that just ate a donut.  

It's bad enough when the mainstream misrepresents and misconstrues scientific studies.  Some of that is to be expected.  But the scientists getting in on the act?  That is inexcusable.  Shameful really.


MacSmiley said...

Found this tidbit at Scientific American regarding the difference in HFCS metabolism in mice/rats versus humans:

Not only do many worrying fructose studies use unrealistic doses of the sugar unaccompanied by glucose, it also turns out that the rodents researchers have studied metabolize fructose in a very different way than people do—far more different than originally anticipated. Studies that have traced fructose’s fantastic voyage through the human body suggest that the liver converts as much as 50 percent of fructose into glucose, around 30 percent of fructose into lactate and less than one percent into fats. In contrast, mice and rats turn more than 50 percent of fructose into fats, so experiments with these animals would exaggerate the significance of fructose’s proposed detriments for humans, especially clogged arteries, fatty livers and insulin resistance.

Is Sugar Really Toxic? Sifting through the Evidence

Bris Vegas said...

Humans evolved from fruit eating apes. You would expect us to have an exceptionally high tolerance to sugars from our evolutionary background. The real world tends to support this idea because fruitarians tend to be very lean despite consuming vast quantities (up to 10Kg/day) of fruit.

Rats on the other hand evolved to ferment complex carbohydrates and fibre as their primary energy source.

Bris Vegas said...

The rats get fat because they are prevented from exercising. Rats that are allowed to exercise normally do not get fat or suffer metabolic disease even when fed a CAF diet.

Rats are naturally super athletes. The "average" untrained lab rat has an aerobic fitness level as high as a human Olympic marathon runner and will voluntarily engage in prolonged high intensity running.

carbsane said...

No doubt this contributes, but when given a species appropriate diet they fare OK. (I've cut into some fatties in my day that got that way on standard chow, so make of that what you may). Still, I've also seen a fat rat or three in the wild, and many fat wild mice.

Kade Storm A.K.A. Hedonist said...

Good point, and on the diet front, I have to also wonder if our food supply--discarded stuff--has a hand in the matter. London's also one of the vermin capitals of the world. We have uniquely adapted urban foxes who thrive off of take-out food that people have gotten into a habit of just throw away in discrete corners of roads and streets. Along with these foxes, we've also had a substantial increase in the population of larger rats and mice appearing in these parts over the recent decade. Not that long ago, I actually saw a rat that looked a lot like one of those photo-shopped and exaggerated, obese lab rat memes one would find on the internet... I had to actually re-confirm what I saw, just to be sure that it wasn't a fat cat or something.

Bris Vegas said...

ERRATUM: Rats have a VO2Max of ~160 - TWICE as high as an Olympic marathoner.

The BMR of a rat is FORTY times as high as human [due to the rat trying to maintain body temperature].

When you keep rats confined in a warm confined space hey are going to expend very little energy keeping war or exercising.

charles grashow said...

Response of C57Bl/6 mice to a carbohydrate-free diet

"At least in the widely used C57Bl/6 mouse, high-fat feeding, even in the absence of
dietary carbohydrate, leads to obesity and an associated increase in leptin levels
as well as distinct insulin resistance."

Sanjeev Sharma said...

Kade says: It's not impossible. I used to bullseye womp rats in my T-16 back in London, they're not much bigger than two meters.

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