One goal of long distance hikers is to carry as little weight as is practical. The gear contribution to this goal won’t be addressed here, but the most variable weight in a backpack, a hiker's food, will. How much food can you afford or not afford to carry?
Planning the legs of a hiking trip requires knowledge of how far one can hike each day, for how long, distance between resupply and how much food will be needed among other variables. To estimate how much food to carry, first select an equation from Table 1 to calculate your BMR (basal metabolic rate). This is the rate your body uses calories either from food or its reserves while quietly resting or sleeping. The idea here is to balance the calorie intake from food to those expended each day so the body’s weight can be maintained.
Note that W = body mass in kilograms. One kcal equals 1 dietary calorie, which is what’s shown on U.S. food package labeling. As an example, a 39 year old male who is 76kg has a 1.159kcal/min. BMR or uses 1.159 dietary calorie every minute while resting or sleeping.
This BMR and the time spent on each type of activity will then be used to calculate how many calories are required each day using the worksheet below. Once filled in, simply multiply across the row ( Time * 60 * Multiplier * BMR ) to calculate the dietary calories, or energy, required for that activity.
See the example below for the 76kg, 39 year old hiker who hikes for 9 hours, sleeps or sits for 12 hours and spends 3 hours setting up or taking down camp, fetching water, fetching wood, visiting the privy, etc.
Table 2 Example
So the hiker above needs to eat at least 5330 dietary calories each day to avoid losing weight. Note that the total time of the three activity types must add up to 24 hours. In both hiking studies 10-20% of the time underway was spent resting along the trail. Time spent on the trail in the A.T. study was 10.9 hours per day, 9 hours hiking and 1.9 hours resting. This left 13.1 hours for sleeping / relaxing and other duties in camp. The estimate above is 190kcal/day higher than the A.T. study’s values. This is in part due to the camp duties not being at a resting metabolic rate which was assumed by the A.T. study.
The hiking multiplier is based on experienced hikers in good physical condition carrying 18-26% of their weight as total backpack weight on real mountainous trails described in the studies below, one in Colorado and the other three on the A.T. in Virginia. In the A.T. study even shoes were included in this weight. The multiplier above is a good approximation, + / - 5%, for 3 out of 4 hikers in the hiking studies referenced below. The fourth hiker’s multiplier for energy use while hiking is 8.68 times his BMR. It’s not clear why this hiker’s energy use was so much higher than the others other than differences in individual metabolism.
These calculations should only be used as an approximate gauge for planning. Since no hiking plan is set in concrete, always err on the side of caution until experience is gained on how much to eat and carry. The fourth hiker’s deficit is 1,300 dietary calories per day if the 6.416 multiplier is used to calculate his food requirements. This is a shortage of about a day’s worth of food over a four day hiking leg.
These calculations do not account for the increased energy required for vigorous hiking. They also don’t account for hiking in cold or rainy weather when more energy is required to maintain core temperature due to body heat being lost to the environment. The BMR equations are derived from a units conversion of the Oxford equations.
With the approximate number of calories needed each day the next question is where should they come from, carbohydrates, protein or fat? The hikers in the A.T. study derived approximately 50% of their calories from carbohydrates and 30% from fat. This was only a 4.5 day study so whether these are ideal ratios for long-term hiking is not known. A study on riders in the Tour de France found they derive 62% of their energy from carbohydrates. The Tour de France is only 22 days long and they don’t carry their food, so how applicable this is to long-distance hiking is also unknown. Olympic athletes’ diet, at the Helsinki games, was 40% carbohydrates 40% fat and 20% protein, but they too don’t have to pack their food.
Fats contain over twice the energy per gram, 9 kcal, versus the 4 kcal of carbohydrates or proteins. High fat content food has the highest calorie density. This makes fatty foods the most efficient in terms of weight carried, provided they are palatable. Table 3 below presents the calories per gram of some common foods suitable for backpacking. The bulk density of these items is also important since backpack space is limited. This is only a consideration of the calories of food. Micronutrients like minerals and vitamins come from a variety of types of food not discussed here.
DeVoe, D. E., R. W. Gotshall, and A. W. Subudhi. “Energy Balance During Recreational Backpacking: A Case Study” Journal of Human Movement Studies, no. 33 (1997): 155-69.
Grandjean AC. "Diets of Elite Athletes: Has the Discipline of Sports Nutrition Made an Impact?" The Journal of Nutrition 127, no. 5 (1997): 874.
Henry, CJK. “Basal Metabolic Rate Studies in Humans: Measurement and Development of New Equations.” Public Health Nutrition 8, no. 7a (2005): 1133–52.
Hill, L. C, D. P Swain, and E. L Hill. "Energy Balance during Backpacking." Int J Sports Med 29, no. 11 (2008): 883-87.