Hi, I've been where you've been. From early programmerhood I've lived on a steady diet on coca-cola, pizza, crisps and other fast food. It was by no means an extreme diet and probably more healthy than an "all-in programmers diet" Even though the diet was pretty unhealthy I still maintained my weight in my early 20-something years.
When I was 30 my weight ballooned into the overweight area, and this was even when I was doing plenty of exercise. I started experimenting with different diets, wanting to find something that I could actually enjoy, didn't leave me hungry and didn't require preparation. Some diets worked health-wise but was too complicated and too boring, I've finally managed to find a diet that suits me, it might not be the one that suits you but I thought I mention it anyway.
The first thing you need to do is to stop eating sugar and that includes any High fructose Cornsyrup. I stopped having sugars in my coffee and eventually got used to it. Soda's was harder, I've eventually learned to enjoy carbonated water with meals and drink coffee and tea for programming fuel (A habit I plan to experiment with dropping)
The next thing is to cut out any fried food. It's a no-brainer since it's easily one of the most unhealthy things you can eat. Not so much for the fat content (which weirdly isn't as unhealthy as you think) but because fried food is loaded with carbohydrates.
Next you need to find a plan for what you actually should eat. I tried to find fast food alternatives that I could enjoy but that was more healthy, things like wook, thai food and sushi. It'll be a bit more expensive but you'll save lots of money from not drinking soda/candy and other crappy snacks
Eating out all the time is boring and expensive however, and the food isn't always that good so you need something healthy you can cook at home. My rule is to build meals around a quality protein (fish/beef/chicken) and have that with a vegetable that provides carbohydrates. Lenses, spinach and beans are especially good. Mix that with some other vegetables, spices and a non-carb sauce (ie bernaise) and you have a very nice healthy meal for the same price as eating out that you can prepare in 3 minutes. Hamburger patties isn't as healthy but since they're easy and probably more healthy than the alternative feel free to endulge.
Yeah, and no bread, rice, pasta, grain, potates, candy, fruit juice, cereals either if you can manage.
Eat eggs for breakfast, like 3 eggs in an omelett with some sallad and an avocado
The really good thing about this diet in contrast to other I've tried is that I'm not hungry, the cravings for sweets and snacks has essentially dissappeared and I need less portions of stuff.
This might sound extreme and I don't recommend you do everything at once. Start shifting parts of your diet and se what works, try having some of these meals and see if you like it.
Finding a diet that fits one taste and lifestyle is a continous process so take it one step at a time.
I think my diet pretty closely follows the Paleo Diet (though I don't really subscribe to all of it). A really good book to read is Why We Get Fat: And What to Do About It by Steve Taub