I hear this story almost every day. Someone sits down and says, “I used to have a cast iron stomach. I could eat anything. But now I look at a slice of pizza or a bowl of pasta, and I feel terrible.”

If that sounds like you, you are not alone. And the good news is that it is usually not permanent.

In my experience, food intolerance creeps up because of a perfect storm of changes inside your body. There are three main factors at play.

The Gut Barrier

Your gut has a lining that works like a filter. When that filter gets damaged, a condition we call Leaky Gut, food particles that should stay inside the gut start leaking into your bloodstream. Your immune system sees those particles as invaders. Suddenly, it starts attacking foods it used to ignore.

Your Digestive Chemistry

Your body is like a chemical factory. It makes digestive enzymes to break down proteins, fats, and carbs. But as you get older, that factory slows down. You simply do not produce as many enzymes as you used to.

Here is something most people forget. Stomach acid. Acid is critical for digestion. It activates your enzymes and tells your stomach when to empty. But as you age, you make less of it.

And if you have been on acid-blocking medications for years, that can make things even worse. Those drugs turn off the very thing you need to break down your food.