What happens when I stop and restart during a long run?

Ok, where to start....

If you are a beginner, there is NO NEED to be pushing an 18-20 mile long run right now. It's just not necessary. Your long run should total around 20% of your weekly mileage - no more than that. I'm not saying it can't go over by a mile or two once in awhile, but I doubt you are running 100mpw at the moment. If you are, you shouldn't be.

The purpose of the food/gels/fuel is to KEEP you going. You shouldn't be taking them once you already feel fatigued or you have run long enough to deplete most of your glycogen stores. Because you have only been running since January it is doubtful that your body does not feel tired around mile 12. This doesn't mean I am saying you are in bad shape, it means that you need to fuel SOONER than mile 12.

I would ingest something around the first 30-45 minutes of your run. After that, have something ever 20-30 minutes if you are going for longer than a 90 minute run. It's not always important to hit a specific amount of miles. Sometimes it's better to simply increase your long run by 5-10 minutes every week, or every other week. Also, are you only eating or are you drinking fluids as well? What are you eating before your long runs?

It might sound like a lot to eat every 20-30 minutes, but it's not. It doesn't mean you need to eat an entire power bar every 20 minutes. If you can't handle the gels, I suggest getting a couple small packs of "Shot Blocks" or fruit snacks/gummies. Let your body adjust to eating them. Nothing is going to feel great in your stomach while you are running, but long runs are a great time to teach your stomach to handle small amounts of food because you are going to need to rely on it during your marathon, especially if it is your first one! I don't know if there is a scientific explanation for why you can feel great while you are running but crappy once you stop. I'm sure there is... but there is nothing wrong with you because you stop running at mile 12 and then find it hard to start again. Sometimes when you are in the groove/zone it's hard to pick up on just how much stress you have alread put your body through and what is going on inside. Once you stop, I think your body starts to cool off quickly, especially if you are tired...your breathing might be fine but a 12-14 mile run (when you still have more to finish) is a VERY long run for a beginner. You are putting yourself through more stress than you realize . Also, just because you don't feel hungry doesn't mean you are already in calorie debt that is hurting your run. I never feel hungry right away during or even after a run. But I know I need to eat during long runs and also directly afterwards if I want to recovery/fuel properly.

If you don't like stopping, then you have to learn how to do gels. At first, you might gag a bit, but you get used to it.

Why is starting harder to do after stopping? It's Newton's law; a body in motion stays in motion and a body at rest stays at rest unless acted upon by an outside object. It's hard to regain motion.

It is hard to get back going after you stop for any length of time. There is a huge difference between walking through an aid station during a race and stopping for several minutes. While you are running, the endorphins sort of mask the pain and stress you are putting on your body, but once you stop, the stress catches up with you and you stiffen up. So, try and minimize the time you are stopped.

IMHO, you sound like you might be pushing the distance too hard. 18 - 20 milers for a beginner is a lot. I'm not sure what your pace is, but if you are doing this at anything slower than 9m pace, you are subjecting your body to a LOT of pounding. Check your cadence on these long runs. If you are plodding along at around 160 steps / minute, maybe you just aren't ready for this distance yet. The running magazines create this mystique about marathons, but I suspect all this hyping is the cause of a lot of injuries. I'm sure it sells a lot of shoes though. Distance isn't the end-all and be-all. Lots of great runners never do a marathon.

you didn't mention what you ate.

Frozen North has nailed it. Learn to love the gels, try different flavors and brands until y0u find one you can stomach.

Trying to eat solids while running is no way to train for a marathon. Jells and a water or energy drink as a chaser are the way to go.

Happy running. I admire your pluck.

There was an article in the June '09 Running Times that offered the idea of using time as your measuring stick, rather than miles. Everyone doing a marathon is doing the same distance, the difference being the faster runners do it in a shorter amount of time, and therefore are stressing their bodies less during the race. The author proffered that for slower runners, training should be by time, i.e., if you estimate at your race pace that it will take you 4 hours to complete the marathon, then you should be gently upping the amount of time you run during training, not to judge how many miles you rack up. This doesn't answer your question about your energy level and intake of food/gel during a run, but I thought it was worth sharing for a fellow slow runner:)

IMHO, it's better off to become efficient at a good pace then to improve the distance than the other way around. If you must eat during an 18 miler, it's a sign that your body isn't ready to go 26, no matter how much you eat.

You probably don't like hearing it, but I think you're better off improving your 10k or half marathon with consistent mileage day in and day out. Then, once your legs are very comfortable with running a lot - and your energy stores are used to supplying it - then putting in the 18-20 milers to get ready for a good marathon is appropriate.

You'll know when you ready for a marathon when, if you wanted to, you could go 20 miles strong without eating anything.