Someone told me that I should gut load my crickets before I feed them to my lizard.
What is gut loading, why should I do it, and how do I gut load my feeder crickets?
Gut loading is the process of giving your live-food animals a diet intended to enrich them nutritionally. It's exactly what it sounds like: you load up the feeder animal's gut with something you want to give to the animal that will eat it. It a sense, you're basically using the feeder as a vehicle for the pet's supplements. It's not a technique you can only use with crickets: it works with any live food that eats, though it's less important when your food animals have more nutrient-rich bone and organ meat, like mice. And it's not something you'd only do for lizards, by any stretch.
When I've kept feeder crickets in the past, I used a vitamin-rich cricket gel (probably Fluker's, I think) as their main diet. These are pretty common, because crickets aren't hugely nutritious by themselves; if you're feeding your crickets a store-bought diet, check the label, because you might already be gut loading them. That's all gut loading comes down to: the crickets ate the gel, than the animals I fed them to benefit from the vitamins. With some animals I supplemented that by dusting the crickets with a calcium-rich powder right before feeding. That's not gut-loading, just another easy method of enhancing live food that can sometimes be helpful.
Whether or not you should gut load live food depends on the nutritional needs of your pet, and how well those are met by the diet you can provide. Often you do this because the feeder itself isn't nutritionally balanced for the pet, or because the pet has a particular dietary need that can't be easily filled otherwise. Non-carnivorous lizards tend to need calcium and vitamin D supplements in captivity, so the dietary cricket gels you can buy are great.
If your particular pet (lizard or otherwise) needs a different balance of fats and proteins, or even vegetable matter, gut loading crickets won't do anything to address that. So think of gut loading as a good way to fill in small nutritional gaps, rather than the foundation of the diet itself. You also have to make sure you're not overdosing any particular nutrient, but this is true of any diet you provide. I've heard of many more problems due to a lack of calcium and vitamin D than I have from too much, and I suspect you would need to really overfeed your lizard for any gut loaded supplements to become a problem.