Keeping elephants Paleo

I've been reading Animals Make Us Human. From the chapter on zoos:
Zoo nutritionists are often concerned that the treat will be bad for the animal's health, especially if it is something unhealthy like grain or marshmallows. To get around this problem, you can use very small amounts. Animals can be rewarded with as little as a teaspoon of grain. One keeper I met learned that an elephant will perform for a single miniature marshmallow.