Your size would never determine how healthy you are. But if you stuff yourself with too much food and other intakes such as beverages, cols, soft drinks, etc, would lead to weight gain and later on a stage where you might become obese too.
How to maintain a healthy weight?
1. Avoid being a couch potato
Include adequate physical activity in your daily routine. It can be, yoga, walking, jogging, cycling, swimming etc. Don't wait to hit the gym if you can't.
2. Eat less food, more often
Spread out your meals to feel satisfied throughout the day. Eating five or six smaller meals instead of having two heavy meals can make a big difference in your energy levels. It will also control cravings.
3. Stay hydrated
What often feels like hunger can actually be thirst. So before you each for a calorie-laden snack, drink enough water.
4. Don't deprive yourself
Don't lose weight by not consuming enough calories during the day. Never let yourself get to the point where you feel like you're starving. It will only make you overeat later.
5. Make smart snack choices
Go anti-white-avoid food items with sugar, white flour and too much salt. Instead of chips, cupcakes or chocolates, choose from the following: an apple, yogurt with flax seeds, a handful of almonds and walnuts, vegetable sticks, etc.
A lot of people consume magic pills and also indulge in fantasy food items simultaneously. But this does not bring out any difference.