I don't know about your wife, but you are absolutely not healthy. 112-115 lbs at a height of 6ft is not a healthy weight. Because so few people in western society follow proper eating habits, people have a badly skewed version of 'healthy'. We tend to equate 'not fat' with 'healthy'. You're not obese (the more common unhealthy condition), but make no mistake . . . your body is not well right now. You should put on weight . . . probably in the range of an extra 20 lbs at a minimum. You don't need a new diet, you need to wrap your head around basic normal eating habits.
Some important facts to start out with:
- More calories in at same rate of exercise = more weight gain.
- Fast metabolism is a myth. Without measuring everything that you eat on a given day, you are overestimating the number of calories you eat.
- Skinny people need exercise just as much as fat people. You can be incredibly unhealthy without being fat.
If I were you I would start a journal and begin tracking everything that passes my mouth during a day (you don't need to do this for the rest of your life, but you should do it for a couple months so that you get a better idea of how many calories you are honestly consuming). At your height, you should be eating at least 2000 calories a day if you live a completely sedentary life. Any exercise that you do will add to that number. If you only eat two meals a day, you will probably feel uncomfortable eating this much food. Try snacking between your meals, having a late breakfast before lunch (since you don't like to eat in the morning), and having a snack before bed time.
At this point, the single most important thing you can do is eat more. If you want to get really picky, your macro nutrient break down should follow roughly a 40-30-30 split of carbs-protein-fats. These numbers aren't written in stone, they can swing slightly higher or lower depending on lifestyle factors. If you want to follow a vegetarian diet for example, you want to slightly boost your protein intake and cut back on the carbs a bit (since vegetable protein isn't the greatest quality, it's not a bad idea to increase the amounts your body gets). It may take a while to get your body used to normal, non-eating disorder habits. If you care about your health at all though, you should spend some time doing this.
What foods should you be eating? This isn't rocket science. Good protein sources (includes chicken, fish, pork, turkey, eggs, greek yogurt, cottage cheese, etc.), good carb sources (includes rice, pasta, potatoes, bread, quinoa, millet, oats, etc.), good fat sources (includes olive oil, nuts of all kinds, avocado, seeds). Cook your own foods as much as possible so you can control the sodium levels, and the macro nutrient breakdown.
Now on to exercise. Can you run three miles in twenty odd minutes? Do 30 pushups? 10 pullups? 100 situps? Carry a 100 lb sack somewhere? A healthy person can do all of these things easily, one after the other. If you can't, it's time to stop being unhealthy and involve some regular exercise in your day. You want energy? Your body is a machine that adapts to stresses placed upon it. Right now that machine has been running on empty for many years. Your heart is weak, your back is weak, your legs are weak, you have reduced bone density. You need to stress your body regularly to force an adaptive change to become stronger. Don't be ridiculous about it, but find some activity that you like to do, and start doing it. Walk->jog->run, get some free weights and slowly increase your strength by following a program, do body weight exercises for higher reps. At this point, what you do doesn't matter. You need to do something.
The younger you are, the easier you body handles adversity. You don't have to follow all of the above, but you're begging for health problems as you age if you keep on the way you've been going.
