Stomach acid is a key component we need for our stomach and intestine to digest food and extract nutrients from the food we eat. When alchlorhydria occurs your body loses it's ability to fully break down and extract the nutrients, particularly in proteins, needed to fuel your body. Malnutrition can result from not being able to absorb the protein that you are eatting as you cannot break it down.
When there is less stomach acid within the stomach bacteria can also grow as it is not inhibited by the stomach acid as it should be. The results from this can vary from diahrea and other stomach and intestinal pains and lower electrolytes within the body (dehydration).