is heating. Sour is comprised of earth and fire elements.
The sour taste increases discernment for those suffering cold emotions like fear and stubbornness. For those already sharp minded, it can tip you over to being critical and judgemental.
In the body the sour taste assists digestion but can also increase an Pitta systems as a result of the fire.
Sourdough is popular because the fermented culture assists with digestion. So those folks that have comprised digestive system, it's a revelation that bread doesn't sit as heavy in their system.
However, if you have internal heat avoid it, you are better off eating whole grains. That stubborn fat around the belly is a sluggish liver, which won't appreciate the sourdough bread.