Revisiting the "Cafeteria Rat" Study -- Why Doesn't Everyone Get Fat?
I was thinking these past few days a lot about scatter plots ... yeah, I'm a geek. But in that recent n=21 Ebbeling et.al. study, as chaotic as the plots (and connecting lines in that case) were, they are still instructive. And apparently some think I should be on a mission to cure obesity by finding out why their wives can eat crap and not get fat, I was reminded of the scatter plots in "Cafeteria Rat" study: Cafeteria Diet Is a Robust Model of Human Metabolic Syndrome With Liver and Adipose Inflammation: Comparison to High-Fat Diet.
If you're a newer reader, may I suggest checking out past blog posts on that study: Why We Get Fat ... Lessons from a Cafeteria Rat ; Why We Get Fat ... Lessons from Obese Humans & Cafeteria Rats ; and Why We Get (Sick) Fat - Lessons from a Cafeteria Rat
To summarize that study, they took four groups (n's varied for various legs of this study) of a normal strain of rats (Wistar, not genetically predisposed towards obesity) and fed them ad libitum on one of four diets, for 10-15 weeks.
1. SC control (estimated <5% simple sugars, 12% fat)2. HF chow - 45% fat, lard3. LF - low fat (10% lard & soybean oil) matched to HF chow with sucrose substituted for fat content4. CAF = SC + 3 human snack foods varied daily from a list
Both the regular chow, SC, and LF diets were low in fat, but I think the LF diet would be better described as HS = high sugar, because it was 35% sucrose. Click the table at right to enlarge to see which human snack foods were included. Everything from pork rinds (I'm sure that will bug the LC'ers) to candy to pepperoni to cheese puffs. When offered this and SC, the rats only consumed 15% of their diet from the chow.
Here's one graphic from the paper I haven't discussed before - the food intake:
The caption for this Figure 1 reads: Cafeteria diet (CAF) drives food and fat consumption. Firstly, in "a" we see that SC, LF and HF rats consumed roughly the same calories. The weekly caloric intakes were actually slightly lower for HF (559), essentially equal for SC & LF (~690), but over 30% higher in the CAF rats (908).
How do you make a rat really fat? You feed it foods it will overeat. But this study also has me seeing Lustig smugly scolding us over the evils of how sugar makes us fat, and how they took the fat out of our foods and replaced it with sugar which turned an entire nation into a nation of fructose addicts. Well, in this study, the LF vs. HF rats tests this hypothesis because they could have just used SC for a low fat diet, but they specifically formulated the LF to match the HF diet, but exchanged 35% of the fat content in HF with sugar. Both LF & HF rats got somewhat fatter than SC, despite similar caloric intake, but they didn't become super fat. This might appear to violate CICO, but the efficiency of high fat diets in rats is known, and in that 25% of the diet as fructose study in humans, chronic consumption depressed metabolic rate significantly.
But to get really fat, the rats had to eat a ton of crap. What's interesting, is that total fat intake for the CAF rats exceeded that of the HF rats (around 44 vs 28 grams per week). Now this is because they ate more of everything, but remember, they were offered low fat SC and a variety of junk, like Cocoa Puffs that is that sugar bomb we're told has addicted us to junk food. The macro percents they ended up eating were 44% fat / 46% carb / 10% protein. I can't help but notice the low protein content and am pretty convinced it is one factor driving the overeating. Consume foods with a low protein:calorie ratio and you consume more of them. Fats do not appear to be satiating.
But let's look at the weights. Below on the left, are the weekly mean weight differentials vs. SC (error bars are likely SD, I don't see that in the caption) and the scatter plots of final weights at 15 weeks are at right. Keep in mind, these rats are bred for laboratories and are much more genetically similar than the human species. They were also housed and treated the same, regular light cycles, etc.
Now these are small groups, so doubtful we could draw anything statistically significant if I tried to test some of the things I'm about to point out, but I think its instructive nonetheless. Look at the SC rats -- all clustered right around the same weight. Eating a chow, however CIAB it is described by another blogger, designed for rodents, there is a pretty uniform response. From my past I can attest that normal rats (usually Sprague Dawley and Long Evans) do grow in body weight pretty predictably. Now, give them an unnatural diet -- either replacing 35% mostly starch & fiber carb with fat or sucrose -- and they respond less predictably. But look at the individual data -- several rats in each group gained less weight than some of the SC rats. It's also interesting to note that the distribution is skewed and they are mostly clumped at the low end of the scale with a few high "outliers" (not technically, hence the ""). Most of the rats didn't respond that negatively to these diets, but a couple-three really responded. One might conclude that high fat or high sugar has the potential to dysregulate homeostasis, and when things do go bad, they go really badly. And now look at the CAF rats. Their weights are uniformly distributed. They all got fatter than SC because they ate a lot more. But the response was far more varied -- the biggest CAF rat is almost 3X the size of the smallest SC rat.
Some of these rats are more susceptible to fat or sugar, the rest escape. All of these rats are susceptible to palatable fat + sugar (+ salt/flavors) but some more than others. It's no mystery to me why they would eschew the yucky bland chow for the junk foods. The rats don't know the junk is junk, that it's not good for them, and they don't much care if they get fat. They eat more of the crappy food because it's there 24/7 and nobody's stopping them. What group in our population that's struggling with obesity might resemble these rats the most? Children, and to a lesser extent, young "immortal" adults.
The food, if you can call it that, is clearly obesigenic. But there's a few differences in us humans such as societal norms and daily reminders (clothing fit) of changing girth. We also have the intelligence and ability to control our diet, choose appropriate foods. So while I might come off (get the feeling I am) as holding Big Food blameless and individuals entirely responsible for this mess, I'm actually somewhere in the middle. Clearly advertising and deals entice us to consume more food, but I'd say the cat is out of the bag on this -- if we banned all ads tomorrow it might help the parents who are highly restrictive already control their children, but I've known about the existence of the delicious Scooter Pie since, well, since I have memories. Ad bans would have some effect, perhaps, but I think those who believe they are a solution are being overly optimistic in their projections of what it would do. Then you have the taxing and regulation options ... not a fan. What we need is education, but the various factions will forever argue what the right education is. I'm one who feels that the "breakfast is the most important meal of the day" and all these studies about hungry kids who won't eat if the school doesn't feed them just got out of hand. And because we don't want to stigmatize little Johnny whose mom can't afford to send him to school with a PB&J for lunch, we'll provide the school lunches for everyone -- there are schools that mandate that and don't allow kids to bring lunch from home. And since we can't know if Johnny ate breakfast, well, we'll just provide that too. Enough! What began as a well meaning effort to ensure against under-nutrition has clearly backfired.
Bottom line, CLEARLY the SAD foods have played a huge role in this obesity epidemic. How we stem the tide -- if there is a community that wants to unite behind this -- is to champion real whole food BASED diets in a real world. Probably 80/20 is too permissive for whatever the chosen approach, but 85/15 so long as the 15 isn't going overboard will work. That's 1 day a week.
Unfortunately there are millions of humans who are obese. To us, hand-wringing over singular theories of how we got that way is mostly wasted energy. And I'm sorry, but trying to find why a "naturally thin" person stays that way and can even have a hard time gaining when they try just doesn't help me. For one, it's decades too late for that -- but remember, I was a lean kidlet. For another, if anyone ever figures this out (as if there's only one thing anyway) the solution will be pharmaceutical. Obesity is not fun to begin with. I think preventing it in childhood is paramount, because reversing it is so darned hard and I think behaviors learned young are the most difficult to change as we mature and age. I just think all the things we as a society are doing or want to do about it are missing the mark. It needs to start with the parent, and we now have a generation or three of parents who came of age in this epidemic, so how are they to guide their children (presuming they want to -- abdication to authorities is easier). Oh lookey there, I went off on a tangent.