1. Carbohydrates spike insuline levels in your blood. High insuline levels result in the sleepy feeling. The rate at which insuline is released in you blood can be regualted if you eat foods in combination. For example carbs should always be eaten with protien. Or carbs should be eaten with fats, preferable polyunsaturated or unstaurated. This should mitigate the 'spleepiness factor'.
2. Eat carbs high in fibre. Fibre slows the rate at which nutients are absorbed (including glucose) and therefore helps regulate blood sugar levels, inhibiting the insuline spike described above. So, if you are eating tuna sandwiches on white bread, try whole wheat. Note that not all 'brown bread' is whole wheat.
3. Eat more times during the day. The typical North American diet usually has 3 meals a day with 60% of all calories coming from dinner. Try eating smaller portions, but more frequently, usually 2 - 3 hours apart. For example something like this:
Breakfast: 8:00 AM
Bowl of bran flakes with real raisins added
Skim milk
Snack #1: 10:30 AM
Protien Shake (Banna, peanut butter, milk and whey)
Granola bar
Lunch 12:00 PM
Tuna Sandwich on rye bread (low fat mayo)
Salad with olive oil and viniger dressing
Banana
Snack #2 3:30 PM
2 Low fat yogurt
Apple
Dinner #1 5:30 PM
Grilled Chicken
Baked potato
Side Vegetable (Corn, Broccoli, etc)
Dinner #2 8:00 PM
Grilled Salmon
2 Slices 100% Whole Wheat Bread
Side Vegetable (Corn, Broccoli, etc)
Eating 6 times a day is very difficult at the beginning. It takes a lot of planning.