Runners - what do you eat to lose?

I was trying something like the Fat 2 Fit formula for a while and was getting good results (before all the junk food I ate last week). Basically, I looked at what my TDEE should be at my goal weight and never ate more than that (2600) even if I "earned" it with a good run. On my rest days, I stuck with the MFP numbers (1900) and then didn't really log everything on my long run days. It was working well for me for a few weeks in a row and I'm going back to it this week. After failing to complete my long run last weekend, though, I'm definitely learning the importance of proper fueling.

I'm really interested in how runners - particularly long distance runners - manage their diet to lose weight. I'm running 2 x 6 miles, 2 x speed work type runs (hills, intervals etc - 4 or 5 miles) and one longer run (12ish miles) a week at the moment, getting ready for a half marathon. Given that I also cycle (for fun) and lift weights, as well as some other bits of activity, I burn quite a lot through the course of a week. If I eat back well into those calories, I find I don't lose. But obviously, if I don't eat enough of the exercise cals, I don't lose either. I'm finding the balancing act really quite tricky.

You probably don't lose when you "eat back exercise calories" because those estimated numbers are inaccurate. Try eating no more than 3/4 of those calories and see how it goes. Finding the right balance between activity and calories can be tricky. All the numbers and formulas are just estimates, so you will need to find the right balance through trial and error. Not losing for a couple weeks? Try lowering your calories. Having too many bad days and bonking on your runs? Up your calories. Repeat.

Frankly, it is a bad idea to do tons of cardio while eating at a large deficit. So if you really want to do endurance running, you need to accept that you will need to eat at a smaller deficit and have slower weight loss. Alternatively, you can hold off on doing lots of cardio, try to lose the fat quicker, and then start more endurance training. I am in a similar situation. I want to eventually do a half marathon, but am capping my long run at 6 miles (about 10 K) so I can eat less and lose fat faster. My other runs are 3-4 miles and I usually only run 3 days per week. Another thing to consider is that, when you have a smaller deficit, you have less room for error. So you'd need to be strict with your food weighing/logging. This article might be of interest: http://www.bodyrecomposition.com/fat-loss/why-big-caloric-deficits-and-lots-of-activity-can-hurt-fat-loss.html

I'd very much appreciate it if you could share the way you balance intake an expenditure, and how well that works for you in weight loss terms? I'd like to shed 10lb before my half marathon (just under 10 weeks away), so really want to get the balancing act right over the next few weeks!

Not sure if this is a good goal. I'd try staying at the standard TDEE-15% and see how that goes. As I wrote above, the balancing will have to be decided on more of a trial-and-error basis. One thing you could try is consuming a good amount of carbs+proteins around your training (a few hours before + right after) to help with energy and muscle repair while keeping your carbs lower during other times/days (basically some kind of carb cycling). I'd also suggest that you don't need to do much cardio outside of the half marathon training.
http://www.bodyrecomposition.com/fat-loss/why-big-caloric-deficits-and-lots-of-activity-can-hurt-fat-loss.html

Tappae, that makes good sense to me. My TDEE is coming in at about 2800, depending on the calculator i use (some put me over 3k). But several days a week I burn well over 1000cals, and if I eat everything back, I do seem to end up gaining. I've been thinking I'd stick somewhere in the region of 1900-2200 ish, as I tend to not feel hungry eating this much (even on a big run day, or the day after) and it seems a reasonable intake?

How do you feel on the longer run days? Might be a bit low when you're running 13 miles. Is this including your running or is it just your "sedentary" TDEE?

Berry, at this point in my running life, I'm slow enough that I'm not too worried about increasing race time. Losing weight seems more important long term for running well, so I think I want to focus on that, over performance? (What do you think?)

You'll be able to increase running pace just by losing weight. If your primary goal is to lose weight, I'd focus more on that over running half marathons.