What is the meaning of "nutrient bang for your calorie buck"?
The phrase derives from the idiom "bang for your buck", which refers to getting the most value for a limited amount of money.
In this case, the "calorie buck" refers to the calories ingested (the fewer the better), and the "nutrient bang" refers to the nutritional benefits you'll receive (the more the better) from consuming whatever product the calories come from.
Thats a new one! anyways it is trying to convey the message that for the cost of that many calories, you will get the highest value of the other nutrients. People are conscious about the calorific value while buying products.
Usually products rich in nutrients are more expensive than the products which give big amount of calories (and are also very available easily/cheaper). Eg: Cost of Nutrient Drinks (and another eg here) vs Soda which usually run about $4 for 12 can pack or even cheaper.