All runners are different but the general advice is that you shouldn’t run too soon after a large meal. Meanwhile, it’s usually suggested that runners consume a snack around an hour or so before heading out for a run. What you eat after a run is very important, too.
What happens if you eat a large meal and run after?
Most people need to properly fuel a run, but consuming a large meal – let’s say 600 calories or more of typically protein, carbohydrates and fat – and then running too soon afterwards usually makes for an unpleasant outing.
Common issues will likely include a stitch (in the side or even the shoulder) or stomach cramps, as well as a feeling of being generally too full to run efficiently. Many people suffer with gastrointestinal (GI) distress if they try to run with a full stomach. This is also know as “runner’s trots”.
There are several reasons why most of us can’t run with a full stomach. The process of running "jostles" food up and down in the stomach, which inevitably leads to pain and discomfort.
The body needs time to digest a meal and this digestion process requires energy. To facilitate this, more blood flow is sent to the stomach and other internal organs. This is why people can feel sleepy after a large meal.
While more blood flows to the internal organs, there is less blood available to fuel muscles in the arms and legs. This means that running performance can be compromised if you eat too much, too soon before a run,
The exact opposite happens when we run: blood flow is redirected from internal organs to the large working muscles to provide the necessary energy for muscles to power your run.
What should you eat before a run?
When it comes to what to eat before running, very runner is different – some might choose to eat a main meal, breakfast, lunch or tea, and then wait a few hours and go for a run. If the meal has enough protein, carbs and some fats, you should be fuelled enough to run up to 10k, perhaps even further. If it’s a run of moderate pace, you will most likely have enough energy for the run.
However, if you plan to run further or do a harder intervals session as part of your trail running training plan, you might benefit from an extra snack an hour or so before a run. It depends how long ago that you ate a main meal.
A snack of around 200 to 300 calories might be a small bowl of cereal, Greek yogurt and some berries, or simply a banana. Most people can run an hour after eating this kind of snack.
A piece of toast and peanut butter has more fat and protein, and might take a bit longer to digest, so this sort of snack should be consumed around 1.5 hours before a run.
All this should be tested during training so that if you have a race to enter you know exactly what works for you and what doesn’t in terms of a run after eating.
How about a run after eating nothing?
Some runners swear by “fasted running”. This would normally happen first thing in a day, before eating breakfast. The theory is that the body is more likely to use fat to fuel a run if the body is in a state of being fasted after a night’s sleep. There is a lot of debate about this and it is worth finding out more to see if it will be the right choice for you.
Certainly, some runners find this is an effective form of weight control. However, this is not for everyone and it can lead to issues with lack of energy and feeling light headed or faint. A lack of adequate fuelling can also lead to poorer performance, too.
If you want to try running without food first thing in the morning, you should build up the distances very slowly. There are runners who report they can run for hours on empty but this is not common.
What to eat while running
If you are heading out for a longer run, say a distance of more than a half marathon, you may need to think about what to eat while running. The body will start to lose energy at different rates, depending on metabolism, weight and how fit you are.
Running snacks to eat as you go need to be easy to consume and easy for your body to digest. Small and often is a good rule of thumb. Many people take small snacks such as energy gels, jelly sweets, cereal bars, Babybel cheese and homemade protein balls. Again, you need to see what works for you.
More important for runners: eating afterwards
You should always have something to eat after a run to replenish lost glycogen stores and electrolytes. The advice is to aim for a meal or snack of a 3:1 carb-to-protein ratio 30 to 60 minutes after a run
A good example of a post-run meal would be a protein shake with fruit, a bowl of cereal, bagel with peanut butter, or a larger protein based meal, such as a tuna sandwich or an omelette.
