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.

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