4. Fatigue and weakness
If you eat constantly much less protein that your body would need, you will feel weaker and you will get tired faster, your strength fades away. At the same time, your metabolism also slows down, and it will be harder to keep your balance. In medicine, the symptom is called Hypoproteinemia, and it is quite common among people suffering from anorexia and bulimia and in countries of the third world.