Your body tells you. Unfortunately, some people have a hard time producing enough HCl. This is particularly true when you're older. People over 65 are most likely to have low levels of hydrochloric acid.
Sometimes, stress or illness can also trigger a decrease in acid production.
Antacids and proton pump inhibitors can also play a role in hypochlorhydria (low stomach acid).
Here are some possible symptoms that can bubble up if you don't have enough HCl*:
You miss out on critical nutrients and minerals that have yet to be released through the digestion process. Low HCl has been linked to the inability to digest essential minerals such as magnesium, zinc, selenium and the vitamins B12, thiamine and folate.*
Unwelcome microbes stow away on your food and reside in your stomach and intestines. Research has shown that low stomach acid is linked to pathogenic microbial blooms in the beginning of the small intestine. Some of these microbes occupy the sphincter muscle at the top of your stomach, paralyzing the sphincter. As a result, undigested food from your stomach (along with depleted and sparse acid in the mix) bubbles up, causing heartburn and acid reflux. So, what is considered "acid reflux" is more often a sign of low stomach acid and undigested food particles backing up into the esophagus.*
Digestion of carbohydrates via acidity doesn't stop in the stomach like it should. Microbes that have also survived into your stomach due to the low pH ferment the carbohydrate cause gas and bloating.*
The flow of bile (and pancreatic enzymes are not released), making it harder for your body to finish digesting foods in the small intestine.*
You may experience brain fog and low energy. Your entire body needs the amino acid building blocks of protein to function. Enzymes, neurotransmitters, muscles, connective tissue — all proteins. And if you can't digest protein properly, you can't make these important nutrients. Even worse, some proteins when improperly broken down, can form opiate-like substances that disrupt brain chemistry and development.*