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Hang on... this debate hasn't gone the way I'd hoped. We are all (almost) just saying what we like and/or what works for us (porridge with handful of sultanas and seeds for me).
The OP had been doing some sports nutrition reading, and was hoping to widen that understanding - relating what we eat to what the nutritionalists say we should eat - and how it helps us through a race.
I'd be interested if anyone can shed more light on it. It's quite a while since I read up on that sort of thing, and I've forgotten it!
Whilst it is true that you don't need a special breakfast before a 10K distance, it doesn't really make sense to avoid eating if you have the opportunity and time to do so. If you normally eat breakfast before going to work for the day (or whatever else you're doing), then why avoid it before undertaking an activity with quite high energy demands?
During the night time fast (also known as sleeping ) your stores of liver glycogen are significantly depleted, and there is associated dehydration. The morning meal helps to restock the glycogen and to rehydrate the body, thereby providing energy to meet the demands of activity without further depleting stores.
As to what constitutes the ultimate pre-race breakfast, it really depends on the demands of the race. It needs to contain carbohydrates, perhaps some protein, with limited fat and fibre. The latter two both have the potential for causing GI disturbances.
The carbohydrates should be a mix of both simple and complex carbohydrates, to provide both a rapid and a sustained energy release. The protein is optional, but helps to control the rate of absorption of the carbs (it slows gastric transit and therefore has the effect of lowering glycaemic load - the rate of uptake into the system) and also can assist with controlling hunger during longer events. Protein is the most satiating of the macronutrients.
The amount of food you need very much depends on the race duration and intensity. If you want to go further or go faster there are increased demands on energy, so you need to eat more for a longer distance/faster race. But the more food you eat, the longer you need to allow for digestion if you want to avoid GI distress.
Getting a bit more specific, aim for 2-4g of carbs per kg of body weight, and try to eat 2-4 hours before the race. For most races, this would be getting up pretty early! You can split this into two meals if you want, with a small complex carb based meal first, then an hour or two later, a small simple carb based snack. If you don't want to/can't eat that far in advance, aim for the lower end of the range, around 2g per kg body weight and increase the ratio of carbs in favour of simple, more easily digested forms. As you would now be eating less, it becomes more important to fuel during the race, assuming you are doing sufficient distance to warrant it (half marathon and above).
As you can see, lots of variables! And after all that - what is the ultimate pre-race breakfast? There isn't one single answer. Any combination of foods that provide sufficient carbs and fluid (and protein if you want to include it) will do the job. Porridge is great, toast/bagels/sandwich with peanut butter/jam/banana/etc., cereal with fruit, yoghurt... all are good. If you can't face breakfast early in the morning, liquid carbs are a good option. They require less digestion so can help if you get pre-race nerves/queasiness or are used to skipping breakfast. Something like juice or a smoothie are good options, as are some of proprietary sports drinks.
As always, don't do anything new on race day!
Some people like to be told what to do, others like to understand why
I prefer jam in my porridge.