Your mouth pumps two and a half pints of saliva a day. It moistens and coats food with substances that help the absorption of nutrients. “The enzyme amylase breaks starchy carbs down into simple sugars, which are easier to absorb,” says Dr Kevin Currell, performance nutritionist at the English Institute of Sport. So, foods like bread and pasta are crucial when your muscles need energy fast.
System upgrade: You can increase your saliva before a meal by chewing sugar-free gum for up to 16 minutes, says the American Dental Association. When eating, chew slowly to give the enzymes more time to do their work. “Breaking food down into smaller chunks also prepares it for your stomach to digest it further,” says Currell.
Food stays here for up to three hours after being broken down, ready for absorption in the small intestine. “Your stomach empties out about four to five calories per minute, so a 500kcal meal would stay there for about two hours,” says Dr Anton Emmanuel, gastroenterologist at University College London.
System upgrade: Nibble your way to greatness by eating up to six small meals a day. Fats take the longest time to get their exit papers, beaten by speedy proteins and carbs. “Liquid meals pass through your digestive system quicker than solid ones because there’s less for your body to break down,” says Dr Sheldon Cooper, consultant gastroenterologist at the Dudley Group of Hospitals, and member of the Bournville Harriers. Which means that the fastest possible energy source is a carb drink.
3. Small intestine
The factory floor of your digestive system, this seven-metre tangled tube is where 95% of nutrients are absorbed. “A variety of processes transport nutrients into the bloodstream – from active transport, where they are physically ‘grabbed’, to more passive movements, where nutrients flow through a kind of ‘revolving door’,” says Currell.
System upgrade: Stock up on B vitamins, which are fundamental to your body’s production and use of energy. “They’re also involved in the repair of muscles,” says Steven Hunter, physiologist and senior lecturer at London South Bank University. Research shows that you only absorb around half the B vitamins in supplements, so it’s wise to also eat beef, liver, seafood, dairy and chickpeas to up your intake.
After nutrients have been absorbed into your bloodstream, your liver steps into action and acts as a ‘handler’. It has two primary functions in how your body uses energy:
The energy store
Your liver is responsible for converting glucose to the body-fuel glycogen, and storing it along with vitamins. “When performing for long periods of time, it becomes even more important to preserve the liver stores. You don’t want to run out and hit the wall too early,” says Hunter.
System upgrade: Research by Ohio State University found that a specific carb-loading method increases your glycogen stores by 20%. So rather than ploughing through a gigantic bowl of pasta, simply ‘graze’ on carbs every 15 minutes for four hours. You’re aiming for 30g every quarter of an hour, so have that potato salad on standby.
The energy regulator
As well as storing energy, your liver also ensures your body has a steady supply of it for immediate use on your run.
System upgrade: You can help your body to release energy at a regular pace with breathing exercises that reduce stress. “Chronic stress slows your bowels, so you digest food more slowly,” says Emmanuel. Borrow this technique used by researchers at Indiana University. As well as combating stress and helping your liver, they found it also reduces the amount of oxygen you need while running.
1. Take a fast, forceful breath in.
2. Exhale slowly for 15-20 secs.
3. Repeat. Take 30 breaths like this, twice a day, six weeks before an event and you’ll need up to 4% less oxygen on the day.