We spend so much time fetishizing food these days that we rarely think about its primary role as fuel. But if you’re into high-impact sports or survivalist planning more than tapas and molecular gastronomy, io9′s Charles Jane Anders has some advice on how to pack the most energy into a single serving.

Needless to say, just because something is high in calories doesn’t mean it is a good energy source—tucking into a burger and fries is likely to leave you wanting a nap more than anything. So what’s the best option? Anders spoke with a few nutritionists and zeroed in on two somewhat surprising food choices for those seeking pure fuel: milkshakes and avocados. These items have the most calories per ounce, so you don’t need to gorge in order to get a boost from them.

[via io9]