An Unbiassed View of What We Should Eat . . . From a Rat

In nature animals must choose a healthy diet based on what tastes good. This doesn’t work for modern humans — lots of people eat poor diets — but why it fails is a mystery. There are many possible reasons. Are the wrong (“unnatural”) foods available (e.g., too much sugar, too little omega-3, not enough fermented food)? Is something besides food causing trouble (e.g., too little exercise, too little attention to food)? Are bad cultural beliefs too powerful (e.g., “low-fat”, desire for thinness)? Is advertising too powerful? Is convenience too powerful? Lab animals are intermediate between animals in nature and modern humans. They are not affected by cultural beliefs, advertising, and convenience (the foods they are offered are equally convenient). Their choice of food may be better than ours.

Nutrition researchers understand the value of studying what lab animals choose to eat. In 1915, the first research paper about “dietary self-selection” was published, followed by hundreds more. The general finding is that in laboratory or research settings, animals choose a relatively healthy diet. There are two variations:

[1.] Cafeteria experiments with chemically defined [= synthesized] diets showed that some of these animals, when offered the separate, purified nutrient components of their usual diet, eat the nutrients in a balance that more or less resynthesizes the original diet and that is often superior to it. [2.] Other animals eat two or more natural foods in proportions that yield a more favorable balance of nutrients than will any one of these foods alone.

Both findings imply that housing an animal in a lab does not destroy the mechanism that tells it what to eat.

Which is why I was fascinated to recently learn what Mr. T (pictured above), the pet rat of Alexandra Harney, the author of The China Price, and her husband, liked to eat. It wasn’t obvious. “We tried so many foods with him and always thought it made a powerful statement that even a wild rat turned his nose up at potato chips,” says Alexandra. “He hated most processed food. He also hated carrots, though.” Here are his top three foods:

  1. pate
  2. salmon sashimi
  3. scrambled eggs

Pate = protein, animal fat, complex flavors (which in nature would have been supplied by microbe-rich, i.e., fermented, food). Salmon sashimi = protein, omega=3. Scrambled eggs = ??

He liked beer in moderation, but not yogurt. “Owners of domestic rats say they love yogurt,” says Alexandra, “but Mr T only liked it briefly and then hated it, even lunging to bite a friend who brought him some. [Curious.] He loved cheese, stored bread for future consumption (but almost never ate it). Loved pesto sauce and coconut.” Note the absence of fruits and vegetables. Alexandra and her husband have no nutritional theories that I am aware of. They did not shape this list to make some point.

For me the message is: Why scrambled eggs? I too like eggs and eat them regularly and cannot explain why.

More Alex Tabarrok’s Thanksgiving post shows the connection between libertarian ideas (economies work better when more choice is allowed) and dietary self-selection.

21 Replies to “An Unbiassed View of What We Should Eat . . . From a Rat”

  1. Well, an egg contains all the essential nutrients to turn a single celled embryo into a living breathing baby chick. Seems logical that they would be healthy.

  2. Interesting. You might want to look at Stephan Guyenet’s recent posts. The studies he mentions suggests that rats will undergo(hot, cold, foot shocks, etc.) near torture while ignoring their rat chow. Was the situation different here?

  3. Scrambled eggs are a mixture of fat and protein, same as the rat’s two other favorite dishes. Now, if he preferred scrambled eggs to fried eggs, for example, that would be a conundrum. Was that the case? Saving the bread shows that he knows that bread will remain edible even though it is stale, while foods rich in protein and fat are likely to rot and make him sick if he doesn’t eat them quickly. Since he doesn’t lack for food, he didn’t need to touch the stored bread. I bet if they didn’t feed him for a day or two he would have gone back to the bread and congratulated himself on his wisdom in planning for the rainy day. But as for the aversion to yogurt, I don’t have a clue. Could it have been tarted up with fruit or jam?

    1. Scrambled eggs are a mixture of fat and protein, same as the rat’s two other favorite dishes

      I am pretty sure they tested many fat/protein mixtures — other meats, for example. These three came out on top..

  4. I am not a very good researcher, and, frustratingly, I’ve not been able to find any documentation, so the following is produced from my possibly (very) sketchy memory.

    Shortly after World War II, Dr. Clara Baker (?) conducted a nutrition experiment in the Chicago (?) area. She recruited 100 (?) babies who had never tasted anything but breast milk.

    Three (?) times a day the babies were set before an array of little dishes containing cereals, custards, scrambled eggs, and many kinds of pureed fruits, vegetables, and meats.

    If the baby stuck its fist into a dish and tried to lick it off, the attendant was allowed to feed the baby one bite of that food..

    At the end of the experiment (six months?), Dr. Baker determined that although the babies’ day-to-day intake was not necessarily nutritionally sound (e.g. nothing but mashed banana for two days), their diets were perfectly nutritionally balanced over the long term, better balanced than the diets of a control group fed by a nutritionist.

  5. You probably need to study more than one animal. Cats tend to be very idiosyncratic about what people food they like. Some like fruit, some don’t. Same for salad, hot pepper-flavored food, and commercial cat foods. I live with cats who aren’t crazy about turkey, but there are so many cat foods with turkey that I bet there are cats who favor it.

  6. Anyone have links to studies on this? (which foods are freely chosen by babies or animals) I think this is actually a valuable way to get insight on the proper human diet.

  7. Eggs are notable for both choline and a high methionine-to-other amino acids profile. The thing about choline is that it’s really hard to get enough of it from anything but eggs. Methionine is easier to come by. However, there may be some evidence to support that amino acid balance is almost more important than the old “complete protein” model. I’m saying this as a person who has speculated that *less* methionine might be healthier than more, but regardless of my personal opinion, Mr. T apparently liked something known to be pretty high in methionine, so I guess it’s his word against mine. (-:

    My rats also hated yogurt, BTW. But they loved tapioca pudding, a formula that does contain a bit of egg…

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