I eat grapenuts and it makes my gas smell exactly like a soiled baby's diaper. could that healthy?

Probably: Its not so much the smell as the fact that more fiber in the diet usually leads to more gas... And that's good. You want to include more fiber in your diet. There are hundreds of health benefits to including more fiber including, weight loss, decreased colon cancer risk, increased heart health, etc. Still, there could be another cause of whjat you are noticing. See your md to discuss.