Depends. Overweight people who just begin exercising bonk easier because they are unable to access fat stores. Fat needs carbs to burn in the Krebs cycle. It's a balance, though, and that's where a nutritionist & a personal trainer can really help. You don't want to scarf down a dozen donuts & ride for ten minutes.

LSD rides (long slow duration) use more fat because the Krebs cycle (where fat is burned) takes awhile. Faster rides at a higher heart rate use more carbs, generally. So, should overweight people do only LSD rides? No. It's the calories in vs calories out equation, for the most part.

Until recently, we thought that intervals burned more fat due to the afterburn effect (the time it takes for your body to return to stasis.) Turns out, the afterburn effect is minimal and intervals often lead to injuries. Intervals do provide variety, though, so they aren't all bad.

There you are. More information than you wanted, probably. I love to talk about personal training.