Its a Mac? Most likely it has too much junk running in the background, a good reformat should fix that.
Stop talking about food I am hungry again now. Also for the mac problem there is a good chance that your storage space is almost full.
How old it is? Apple intentionally slows down its devices when they are old in order to make the deteriorating battery last longer
Same with my mac, but it's not because of storage or memory, have lots of space left. It's normal for Macs to slow down over time. Even when I restored it to production setting and erased everything it still is not as fast as it was when it was new.
When you use an electronic device, it heats up. Heat damages electronics. Therefore, electronics degrade with use. That degradation is almost imperceptible over short spans. If you're only noticing that your years' old Mac is slower than it was when it was new, that could just be a natural thing. On the other hand, if your Mac has slowed considerably in a short span, there's probably something else going on. Next time your computer seems to be running slow, check your task manager to see if anything is hogging your RAM or CPU. If either of those is near 100% useage, then figure out what's causing that and fix it. If you can't find anything wrong, try wiping everything and starting from scratch. If that doesn't fix things, then you probably have a hardware issue.