Canberra Marathon Festival: What you should eat to run your best marathon

Researchers used to think the body had finite limits for how much fluid and carbohydrate it could process mid-run. But studies show that with training, your body can adapt to much higher limits. One study found that fit male runners were comfortably able to more than double their fluid intake over five 90-minute runs. Another study from the Australian Institute of Sport found that with daily training, cyclists who consumed about three times more carbohydrate than the current recommendations for mid-run fuelling increased the amount of carbohydrate their intestines could absorb. The key is to practice taking in high amounts of carbs and fluid during training, so that your gut is well adapted by race day.

During most weeks of marathon training, your muscles never have a chance to fully reload with glycogen. Runners and other endurance athletes simply need to back off on training for a few days and muscle enzymes responsible for restocking glycogen will gradually begin to store more carbohydrate, helping build up your energy reserves for race day. Make sure you're consuming at least three grams of carbohydrate per 500g of body weight during this time period to meet your needs.

Boosting carbohydrate intake to 3.5 to four grams for every 500g of body weight will further increase your glycogen stores. The key is to back off on fat and protein to help balance your kilojoule intake and avoid gaining weight. Even with those cutbacks this higher carb intake may supply too many kilojoules for your needs. If you notice you start to gain more than a couple of kilograms, tweak your diet, reducing your carb intake until your weight balances out.

Limiting high-fibre foods such as bran cereals, whole grains, and large amounts of vegetables for the few days prior to a race has multiple benefits. Research from the Australian Institute of Sport shows that eating a lower-fibre diet can help lighten the weight of material in the intestines. This can reduce your body weight (potentially leading to faster running times) and may help you avoid the need for a mid-race pit stop that would otherwise add time to your race.

A pre-race meal supplies extra carbs to top off glycogen stores, particularly in the liver, which will help steady blood sugar levels during the race. Aim for .5 to one gram for every 500 grams of body weight (about 75 to 150 grams for a 68-kilogram runner) - but only eat the higher range if you have four full hours to digest. Back off on fats and keep protein to about 15 grams or fewer - both nutrients take longer to digest. A study from the University of Minnesota found that for novice marathoners, eating a high-carb pre-race meal was an important predictor of finishing times: runners who ate ample carbs ran faster than those who skimped.

Put your training to work: Fuel up with at least 30 to 60 grams - and up to 90 or 100 grams if your gut tolerated it during training and you're planning to race hard - of easily digestible carbs per hour. Fluid intake should also go according to training, keeping the temperature in mind; sweat losses will be less in cooler weather. Studies show mild dehydration (one to two percent loss of body weight) will not hamper performance, so avoid over consuming fluids. Not only will it make you heavier, but also you'll risk diluting electrolytes, a potentially serious medical condition. If you feel yourself start to fade during the second half of the race (and who doesn't?), try a hit of caffeine (30 to 50 milligrams) from an energy gel, chews, or drink. Studies show this modest amount helps boost alertness and may provide a second wind.