Sunday, August 10, 2008

Rats on Junk Food

If diet composition causes hyperphagia, we should be able to see it in animals. I just came across a great study from the lab of Dr. Neil Stickland that explored this in rats. They took two groups of pregnant rats and fed them two different diets ad libitum, meaning the rats could eat as much as they wanted. Here's what the diets looked like:
The animals were fed two types of diet throughout the study. They were fed either RM3 rodent chow alone ad libitum (SDS Ltd, Betchworth, Surrey, UK) or with a junk food diet, also known as cafeteria diet, which consisted of eight different types of palatable foods, purchased from a British supermarket. The palatable food included biscuits, marshmallows, cheese, jam doughnuts, chocolate chip muffins, butter flapjacks, potato crisps and caramel/chocolate bars.
It's important to note that the junk food-fed rats had access to rat chow as well. Now here's where it gets interesting. Rats with access to junk food in addition to rat chow ate 56% more calories than the chow-only group! Here's what they had to say about it:
These results clearly show that pregnant rats, given ad libitum access to junk food, exhibited hyperphagia characterised by a marked preference for foods rich in fat, sucrose and salt at the expense of protein-rich foods, when compared with rats that only had access to rodent chow. Although the body mass of dams was comparable among all groups at the start of the experiment, the increased energy intake in the junk food group throughout gestation was accompanied by an increase in body mass at G20 [gestational day 20] with the junk food-fed dams being 13 % heavier than those fed chow alone.
Hmm, this is remarkably reminiscent of what's happening to a certain group of humans in North America right now: give them access to food made mostly of refined grains, sugar, and industrially processed vegetable oil. They will prefer it to healthier food, to the point of overeating. The junk food then drives hyperphagia by interfering with the body's feedback loops that normally keep feeding behaviors and body fat within the optimal range. These data support the hypothesis that metabolic damage is the cause of, not the result of, "super-sized" food portions and other similar cultural phenomena.

The rest of the paper is interesting as well. Pups born to mothers who ate junk food while pregnant and lactating had a greater tendency to eat junk than pups born to mothers who ate rat chow during the same period. This underscores the idea that poor nutrition can set a child up for a lifetime of problems.


Sue said...

Regarding the junk food rats that ate 56% more calories. Did it equate to about 56% more food gram for gram they ate or did it end up been 56% more calories because the junk food had more calories per serve than the rat chow?

Stephan Guyenet said...


Good question. The rats ate 40% more food by weight, 56% more by calories. So they weren't just eating more because the food was denser in calories.

There are some interesting experiments in rats where researchers diluted their food with indigestible fiber. Rats will eat until they get about the same number of calories as rats on un-diluted food. There really does seem to be a metabolic "set-point" of weight and caloric intake that animals (including humans) prefer.

Dennis Mangan said...

Hmmm, rats eating fattening food got fat. And they preferred it to rat chow. Human analogy: people prefer donuts to oatmeal, and are likely to get fat on the former. I'd say we already knew this.

Unknown said...

I've always thought of portion size (or control) as a purely cultural phenomenon but it's interesting to learn of the metabolic causes for it.
It ties in with the idea of processed and refined foods being similar to addictive drugs. Gives new meaning to that Frito Lays slogan "you can't have just one".

Stephan Guyenet said...

Ha ha, maybe it should say "you can't stop eating them until you're dead".

Debs said...

To say nothing of "coo-coo for cocoa puffs."

I think the theory that overeating is a symptom rather than a source of the problem makes a lot of sense. Seems like the thing to fix is the damaged metabolism because of the other havoc it could be wreaking. Forcing someone with a damaged metabolism to eat less isn't going to do much good.

Hey, how much do rats like rat chow? Maybe they're crazy about it, but I can imagine if I were a rat living in a lab, resigned to a life of rat chow, and someone gave me a bunch of those brownies I was always seeing the grad students get to eat, I'd be pretty psyched too.

Food Is Love

Stephan Guyenet said...


Yes, it makes a lot more sense than the "we're fat because we don't have the iron will of our ancestors" explanation. Previous generations were eating until they were full, just like we do today.

Rat chow is miserable stuff. It's not too surprising that they showed a preference for junk food. I don't think that detracts from the finding though. It may suggest that they're overeating because of the superstimulus of the junk food. Although I think it's probably more complicated than that.

AngloAmerikan said...

There is a lot more choice with food now. When I was a child, back in the sixties and seventies in New Zealand, we rarely had sweets, cakes or soft drink. Fruit juices were drunk at Xmas time, eating out was maybe once a year and you needed a doctors prescription for margarine. There was no McDonalds and only the super rich could afford KFC or Pizza. It was like North Korea except we had heaps of lamb, milk, butter and potato.

Now everyone lives like royalty except without the self control.

Stephan Guyenet said...

A doctor's prescription for margarine! That's funny in so many ways.

They should have been giving out doctor's prescriptions for grass-fed butter.