If you are eating because you are hungry and stopping when you feel full, that’s not gluttony. Actually, some people need to eat in this manner, many smaller meals throughout the day instead of the standard American three meals, breakfast, lunch, and dinner, dinner being the largest meal before bedtime. It’s generally better to eat one’s main meal midday for in the morning than close to bedtime. It’s the way the economic and educational systems in the US are set up that have come to dictate when and how much one eats.
Gluttony would be continuing to eat even after full, for the pleasure of eating. If done somewhat, not regularly it is a venial sin. If it is habitual, to the point of becoming physically ill, or of eating a peculiar, unhealthy, or in a compulsive manner,nit is probably a mortal sin.