Most of the issues you have listed are quite common in children of this age group. Usually children prefer sweet foods rather than vegetables. You have to try to control the availability of sweet things and serve vegetables in different forms.
Regarding his not being able to take defeat is also common at this age. Encourage his achievements and help him learn that everyone cannot win. If he loses, do not be judgmental, but show him how there is always a next time. Model healthy sporting spirit in him. Do not compare him with his sibling or with other children.
Explain to him how talking in class is affecting his performance, and how he can improve by paying more attention. If he shows persistent attention deficit in all areas, you should consult the school counsellor or a good psychologist. But his behaviour seems to be normal for his age.