What things can happen to food in stomach after it is consumed?

Digestion. Acid in stomach starts breakdown in food as first vital step in digestion. If this is low (from aging or from taking acid blocking medicine like Prilosec or nexium), then will start to interfere with digestion. Acid is also vital for absorption of nutrient like calcium. Again if low will interfere with normal digestive process. This will ultimately interfere with nutrition and health.