Food and Drink
Food satisfies both a physiological and a psychological requirement. These both become more significant when hill walking.
Our bodies take energy from food when we exercise and the more strenuous the exercise, the greater are the demands.
The actual amount of energy needed depends on a number of factors:- your body weight, age, gender plus the distance and total height gain of the walk.
In hill walking, your muscles need both carbohydrate and fatty acids. If the available carbohydrate is reduced too much, then you will have to slow down. Good food also provides the motivation to complete - and enjoy - your expedition.
The most important requirement is water. When we exercise, our body temperature is controlled by the evaporation of sweat from the body surface. If your body is dehydrated, then heat can't be dissipated in this way. This can result in the rapid onset of heat exhaustion.
Until recently it was felt that you should not wait until you're thirsty before having a drink. However, the current recommendations are that you should be guided by your perception of thirst and should try to match your fluid intake to your rate of sweating.
In this way, you should maintain an adequate level of hydration without running the risk of 'over-hydrating' - a condition that occurs when the salt content of the blood is diluted (aka Hyponatraemia). If untreated, Hyponatraemia can have very serious effects on all the main organs (especially the brain) and muscles.
Water is probably the best option - hydration packs are useful for taking on board water whilst on the move. On longer days, include drinks that include electrolytes which will be helpful in maintaining your sodium levels.
You need to have enough food with you so that you can avoid exhaustion due to lack of energy. Exactly how much will depend on the factors outlined above (i.e. age, weight, gender, distance, height climbed).
You'll want to have food which is light to carry but which is 'energy dense'. Foods which are high in carbohydrate are a good idea.
A lunch box for a day trip might include:
2 sandwiches (e.g. cheese or peanut butter)
Bar of chocolate
Some dried fruit/cereal bar
2 litres of water
Probably the most effective way to consume food when walking is to eat 'little but often' throughout the day.
It's also very important that your day begins with a good breakfast eaten ideally about an hour before the walk start.
At the end of the day, your body will need to refuel. It does this most effectively within 2 hours of the end of your walk. Again, it is foods which are high in carbohydrate (e.g. banana, chocolate, cereal bar) which are most effective. Also consider some saltier food if you've had a particularly long day and/or have sweated a lot.