Hello @Danny_Ho
Yes, i also have gas issue when i stop eating meat.
Dampness is an idea in chinese medicine. Some foods are cold in nature, like melon, coconut (hence, you tend to find them in tropical or hot area). Some foods are hot in nature, such as garlic, onion, meat, dragon eyes, and so on.
I follow the diet of Buddhism, so no meat, no egg/milk and other pungent roots, such as garlic, onion shallot, leek, Asafoetida. Science shows that garlic, unlike other food, can penetrate our brain barrier. Hence it can affect your brain directly, so it is best to avoid if you are cultivating for a quiet mind (for me, they induce emotion and sex urge).
Now, dampness means the food we eat are cold in nature, such as mostly veggie. Veggie is mostly water and fiber. The more cold stuff we eat, the colder and wetter is our body. Yet, i can have trouble to eat too much peppers/ginger to remove the coldness in the body because my stomach cannot take so much heat at once. Hence, dampness has always been an issue for veggie/vegan eaters if you don’t eat garlic/onion.
As for gas, i think you need probiotic. It helps to solve part of my issue. Then with max heal, it heals 80% of it. The rest, i need to eat slower, chew longer, and eat with less rush.