The key here is whether or not your fish is very active in that space and also if your betta needs to compete at all for food. I found that Rusty fiercely began competing for food the moment I put the catfish in. He eats more than the average betta but only because he steals food from them. If you're feeding other fish in the same tank rather rich food (like worms for instance) then don't feed your betta regular food that day, he'll probably snarf some. If he doesn' then don't worry about it. Bettas are the pickiest fish in the world and will normally pick one kind of food to eat, no more. However as Rose said they will act as though you barely feed them at all. Rusty tends to wriggle around excitedly after being fed, looking at me appealingly, basically saying, "Is that IT?" when in fact he's had as much as a betta can safely eat.
Oh how I do know that appealing little wriggle!!!! They all do the "More!" dance. The only one of mine who gets anywhere with it occasionally is Alexander and that is because he is practically a large fry. He gets the minI pellets so since they are about half the size of a Betta Bio-Gold he does get more than the 3 - 4 pellets twice a day. (This information is only pertinent to the users of Ocean Nutrition Atison's Betta Pro) He gets actually more like 6 - 8 pellets twice a day. These pellets are so small they are noticably tinier than any other pellet food I have seen and he is still growing so he gets to have 4 tiny meals, the 6 - 8 pellets are divided into 2 small meals of 3 - 4 pellets about 30 minutes apart twice a day.
That is very interesting to know about dealing with a very young betta. I'll store that info away in my mental cheek for later. And yeah, it is appealing, that's probably why they do it. BTW, I caught Rusty not merely grabbing a shrimp pellet first but actually grabbing it with his mouth and stealing off with it, as if to deny it to the corys, which were still rooting around for it. However they are too big for his mouth so it inevitably fell out...if they could only get past that opposable thumb thing they could rule the world, hey?