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I'm wandering if mammals that can eat many different kinds of food (omnivores) vary their preference for food not only based on the availability, but also based on dietary needs?

I'm looking at this site Food nutritional content and see that "not all foods are created equal" - the vitamin/mineral and amino acid contents can vary dramatically. Is there some part of an omnivore brain/digestive system that "monitors" the micronutrient density of digested food and adjusts food preferences towards foods that make the diet more complete?

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I want to say yes, as I've heard of cases that people starving afloat on the ocean and desperately in need of Vitamins will eat Vitamin-rich portions (eyes, liver, etc.) first, but I haven't the sources yet. There's also Geophagia, which can be common for pregnant women who are starving for the iron content of the dirt. –  MCM Nov 2 '12 at 15:20
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up vote 4 down vote accepted

For what concerns amino acids, mice rapidly reject meals that are not balanced in essential amino acids and continue to look for other kind of foods. This behavior is called aversion response and it is an adaptive phenomena that can be observed already 20 minutes after exposure to the unbalanced food. The mechanism involves brain sensing of uncharged tRNAs. The significance of the aversion response is to minimize depletion of essential amino acids that can not be directly synthethized but are required for protein synthesis. You can find good reviews in PubMed, for instance Gietzen et al. 2007, Annual Review of Nutrition, and Gietzen and Aya 2012, Molecular Neurobiology.

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Great answer! Reading the 2nd article, I see that there's "rapid recognition of Indispensible Amino Acid(IAA) depletion in the rat brain's IAA chemosensor, the anterior piriform cortex (APC)". –  Alex Stone Nov 3 '12 at 17:20
    
Here's a paper that deals with pleasure in the brain, but also mentions that aversion response to salt can be decreased dramatically, and be replaced by "liking" response when brain experiences sodium deficiency: lsa.umich.edu/psych/research&labs/berridge/publications/… –  Alex Stone Nov 4 '12 at 8:07
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I found that there are seasonal rhythms in the nutrient intake: Seasonal rhythms of human nutrient intake and meal pattern

The article's abstract mentions carbohydrates, while I'm more interested in the micronutrients, like amino acids and vitamins/minerals.

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not sure amino acids can be considered micronutrients like vitamins. –  Gianpaolo R Nov 3 '12 at 10:08
    
That is a very good observation! I'll check the articles above to see if they mention vitamins as well –  Alex Stone Nov 4 '12 at 8:14
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