Bushwalking Victoria's Facebook page includes an article by Ryan Gardner, an American backpacker who proposes that the energy-to-weight ratio (caloric density) should be the primary consideration when deciding what food to take on a pack carry. Ryan holds a degree in Exercise and Sports Science from the University of Utah.
Below is a summary of some of the salient points in the article. Read the actual article at https://www.facebook.com/bushwalkingvictoria?fref=nf.
Ryan's proposition is irrelevant for most day walks, but is something to think about when packing for a pack carry when weight and bulkiness become increasingly important considerations the longer and harder the walk.
Calculating caloric density
You calculate caloric density by dividing the total number of calories an item of food has by its weight. The higher the density the more energy an item packs given its weight. So if there is a choice between similar items – eg, energy bars or main meals – one should take those with the highest energy density.
How much food
How much food you need depends on your body weight and your basal metabolic rate. Basal metabolic rate (BMR) is a measure of the number of kilojoules your body will burn on any given day, without taking into account any exercise you may do.
Essentially, this is how many calories it takes to keep your body alive and ticking over, even if you do not move a muscle.
It's all right for your body to use up fat (what Ryan calls the 'reserve tank'), but it's important that it never begins to start eating up muscle because you need muscle to keep you going during the walk. Unless you are fat, you should not be aiming to lose weight on a walk (even though many of us do!). You will lose weight anyway because a huge amount of energy is expended on a pack carry and also because many people find their appetite drops while on an extended walk.
Tip: Label your food bags/portions with the amount of calories inside each bag.
Ryan does not include fresh fruit and vegetables in his pack carry menu because while they have important vitamins and minerals, they are low in energy given their weight. And energy is what you need on a pack carry. Instead he says you should be eating lots of fruit and vegetables in the weeks and months leading up to the pack carry.
Nuts have a good caloric density and are also high in the good unsaturated fats and Omega-3 fatty acids as well as being high in protein.
The 'sugar crash'
Sugars, or carbohydrates, come in two main forms: simple carbohydrates and complex carbohydrates. Simple carbohydrates are found in things like table sugar and candy bars. Simple carbohydrates provide a quick boost of energy, but that energy level drops off rapidly. The drop off is what is often referred to as a 'sugar crash'. Complex carbohydrates are found in foods like whole grains, rice, and pasta. Complex carbohydrates take longer to digest and as a result provide longer, more sustained energy. Complex carbohydrates do not result in a sugar crash.
For every day healthy living, complex carbohydrates are by far the better choice. However, for backpacking, simple carbohydrates have higher caloric densities and are convenient to eat on the go. So one should eat a breakfast and dinner of complex carbohydrates but consider using 'calorie-dip method' of nibbling simple carbohydrates frequently throughout the day. This way you avoid spikes and drips in your energy levels. So scroggin (that contains lots of nuts) is good!
Ryan prefers not to eat a 'traditional lunch' on a pack carry. He thinks taking a long lunch not only sets you up for a potential sugar crash, but also causes your heart rate to return to normal, making it harder to get going again after lunch.
Preparing for the pack carry
The best thing you can do to help your body run efficiently and recover quickly from the more intense exercise you are doing on a pack carry is to exercise regularly when you are not pack carrying and eat a healthy, balanced diet.