The Lose It app sounds very similiar to the Biggest Loser Club's system. Basically recording calories in vs calories out.

From memory, BLC recommend a daily deficit of between 300-500 calories from exercise. They also recommend that you get within 200 calories of your daily intake allocation, and never below 1200 calories. Their recommended intakes are based on your current weight and current activity levels. For reference, I started out at 1800 cal per day when I was 95Kg. Now I'm at around 67Kg, and my daily allocation is 1500 per day.

If you under-eat, your body will go into starvation mode (though the deficit required to produce that result is not known to me). When I started doing longer rides, burning up to 3000 cal, I asked the BLC nutritionists for advice on whether I should eat more, and if so, what. Their response was that if I felt hungry, that I should feel free to eat more, even if meant going over my normal daily intake allocation (which is based on the assumption that the exercise you do is between 300-500 cal per day - not 3000!). They recommended high protein foods so that I would feel full for longer. Their emphasis was on making sure I ate good food - not processed snacks or calorie-dense rubbish or whatnot. For me, a couple of bananas really hit the spot after a long ride. Boiled eggs are good too.

You need to ensure you don't overdo it. Regular small lots of exercise will produce weight loss. Regular huge lots of exercise will leave you feeling tired, hungry and unmotivated. The key is balance (which you already know, since you're monitoring cals in vs cals out). I can tell you from experience that if you stick to your calorie allocation, and exercise moderately 2-3 times a week, you will lose the weight (28 kilos, gone)! The weight loss I achieved on weeks where I did one or more very long rides (on top of the regular 2-3 moderate sessions) was not substantially different from the weight loss achieved from weeks where I did 2-3 moderate exercise sessions.

Hope this helps

Max