Meat -vs- Meal

But the marketing companies that sell kibble know you’re looking there, so that’s the first place they think of to trick you into thinking there’s more appropriately sourced protein in the food than there really is.
When you look at an ingredient panel, the pet food ingredients are listed from most to least by weight – so whatever contributes the most to the weight of the food will be first on the label.
The weight of the ingredient is measured before the cooking process – not after in the final product that your taking home. And that’s the difference between meats and meals. Meats contain water, which is very heavy, and meals don’t.
Here’s an example.

You'll see in many pet foods that "chicken" (or another meat)  is the first ingredient. 

You might see this as the first ingredient and think the protein in this diet is mainly comprised of chicken – but you’d be wrong. 
Chicken is about 70% water by weight – and the ingredient panel only lists ingredients by weight when they’re added to the food.
Once it’s processed, this kibble will end up as a dry food – and most of the other ingredients that are added to the food are also dry. So that can really make it look like it has more bio-available protein that it really does.
Looking that bag of pet food that contains "chicken" first, and now knowing it was mostly water, take a gander at the GA. The Guaranteed Analysis says it contains 25% protein on a dry matter basis. HOW?

If this food is 25% protein, then where does the protein come from if it’s not chicken? It comes from grains of peas.
So what’s wrong with using plants for protein?
Protein is made up of little building blocks called amino acids – and your dog uses these amino acids for his health and nutrition.
There are several amino acids that are essential. That means your dog can’t manufacture them and absolutely needs to get them through his diet. But plants and grains are an incomplete source of the amino acids your dog relies on. And they might not be as easily digested and used as the animal proteins your dog was made to eat.
But pet food companies love plant-based proteins because they’re much cheaper than animal protein. So they’ll try to use these poor quality ingredients to boost the protein content of the food. This helps the food to meet minimum requirements as cheaply as possible but it leaves your dog open to potential health issues when he can’t use these low quality proteins.