Eating bugs might be the most sustainable option for protein

Most people wouldn't consider eating an insect when they're hungry. Eating insects, which is also known as entomophagy could be the answer to our answer of how to feed our population booming population without destroying our planet.Outside of the United States eating insects isn't as taboo, bugs can even be considered a delicacy. In the image below it shows an example of a market where you can buy bulk bugs by weight.

These bugs are high in protein and also provide other nutrients such as iron, zinc and fatty acids. They also provide a source of protein without the negative affects like that of meat which can lead to cardiovascular disease and diabetes. If you can't see yourself ever being able to enjoy these critters they're are ways to disguise their familiar exoskeletons. Some examples are grinding them into fine powers or flours to be used in baking or blended into smoothies. If the look doesn't bother you but you're more concerned about the flavor they're are many options of preparation.   Popular methods include seasoning and roasting.  Here is an example of a dish below:
 Not  only do these have the capability to provide a cheap source of protein the propagation of these organisms leaves a  much lighter carbon footprint then that of livestock production and processing.
Insects are easy to grow and can be integrated into already existing farms. As our population grows our way of life must grow with it.

Sources and further reading: