Backpacking Science and Privilege: Water

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On long-distance backpacking trips we don’t take the same things for granted that we do at home and as a result we can gain some insights into our privilege and how it affects the way we hike our hikes, and pack our packs. This is the second post in a series of three in which I  discuss how science and privilege influence the way I pack my pack.

  1. Food: Our ability to regulate blood sugar levels (glycoregulation).
  2. Water: Our ability to regulate water and minerals (osmoregulation).
  3. Shelter/Heat: Our ability to regulate body temperature (thermoregulation).

Unpacking my Invisible Knapsack: Water

In 1989 Peggy McIntosh wrote a famous essay in which she likened privilege to “an invisible weightless knapsack of special provisions, maps, passports, codebooks, visas, clothes, tools and blank checks.” What follows is a list of water-based privileges that hiking the trail has made me more aware of:

  • I don’t have to be thirsty. Living in New England in the age of modern plumbing means that this is usually a privilege that I can rely on. Typically all I have to do is walk into the kitchen or bathroom and turn on the faucet to get as much water as I want. On the Appalachian Trail there were frequently springs, streams, rivers, or ponds from which water could be acquired, although during the late summer months many of the springs/streams were dry and more advanced planning was necessary to avoid running out of water and being thirsty. On the Pacific Crest Trail this year (2014) as I hike through the desert in a record-breaking drought, the availability of water will be more of an issue.
  • The water I drink won’t make me sick. First world privilege and modern sanitation means that the water I have access to in my home is unlikely to make me sick. On the trail, the water coming directly out of the springs is unlikely to make me sick, however, water from streams, rivers, and ponds may be contaminated with giardia and e. coli. The streams in Maine (for instance) are often fed from beaver ponds and may be contaminated with giardia.
  • I’ve never been so desperate for water that I’ve knelt down and tried to lap it out of a mud puddle. Walking through the streets of Boston I’ve never been tempted to drink water from a mud puddle. During an uncharacteristic heat wave on a 20 mile day when I miscalculated the amount of water I needed to carry and ran out 5 miles short of the next spring… that mud puddle was a very tempting source of water indeed!
  • I don’t have to pay attention to how much water I drink. When there is a faucet with running water in the room next door I don’t worry or pay attention to how much water I drink because I can always get more whenever I want. On the trail I sometimes end up rationing my water if I start to run out sooner than I expected or if I don’t know when or where I’ll have access to water again.
  • There will be water available when I need/want it. The joys of modern plumbing in a water rich environment means that this us usually true for me. On the Appalachian Trail in the spring, water was abundant, but some knowledge of where the next sources of water were likely to be was useful. On the Pacific Crest Trail in the desert during a drought, I expect that I will need to be much more careful when it comes to figuring out where to get my water and how much to carry.
  • My behavior does not affect the availability and quality of my (or other people’s) drinking water. Typically at home in New England I don’t have to worry about how my behavior is affecting the public water supply. There are also regulatory agencies (like the EPA) which help ensure the quality of my drinking water. On the trail, however, people washing themselves and or their dishes in the rivers and streams can have a direct impact on the quality of the water I drink… never mind whether or not they decide to use the riverbank as their personal latrine.
  • I know that if I run out of water other people will share theirs with me. If people on the trail have extra water they are typically willing to share it. Also, on the Appalachian Trail in regions where water is scarce trail angels often provide water caches along the roadsides for thirsty hikers.
  • I will be allowed to use public restrooms. White middle-class privilege means that I can use most public restrooms without being harassed. Many businesses, however, require that you make a purchase in order to use their restrooms and, as a hiker, seem to be much more confrontational about making sure that you actually purchase something before allowing you to use the restroom.
  • The research that I use to determine how much water I need is based on people that are likely to have physiological requirements similar to mine. White privilege means that this is usually true. Most of the data is, however, based on men and less data seems to be available about women.

Packing My Pack: Water

To ensure proper hydration while backpacking you need to match your fluid intake (from food and beverages) to your fluid losses (through urination and sweating). Dehydration, defined by a 2% drop in body weight, results in impaired physiological and psychological performance, further dehydration can impair the bodies ability to regulate temperature and increase the risk of developing heat stroke. For every 1% drop in body weight from sweat, core temperature goes up by 0.15 to 0.20 degrees Celsius and increases heart rate by 3-5 beats per minute. It is also important to note that over-hydrating can result in electrolyte depletion and hyponatremia. Symptoms of heat exhaustion and hyponatremia are easily confused (dizziness, headache, nausea, and muscle aches), however symptoms of heat exhaustion are relieved shortly after improved fluid consumption whereas symptoms of hyponatremia continue or worsen with additional fluid consumption. On the other temperature extreme, dehydration can hasten the symptoms of hypothermia (click here for an overview of hydration for backpacking).

Though data specific to the hydration requirements for recreational backpacking are minimal, the US military has many similar hydration requirements and a well-established set of guidelines for hydration and fluid replacement (2010). These guidelines are based on the environmental heat exposure determined by wet bulb global temperature (WBGT=0.7Tw+0.2Tg+0.1Td), which includes a measure humidity (Tw, the natural wet bulb temperature), radiant temperature (Tg, the globe thermometer temperature), and dry air temperature (Td, the dry bulb temperature) and as well as the  intensity of the work performed (see the graph below):

Image result for military desert water requirements data

Water Requirements (NOTE: Current Standards State Consumption should not exceed 11.4L/day)

 

A common clinical method for estimating fluid replacement volume is the Holliday-Segar method, which suggests that water loss is related to caloric expenditure. This method was initially developed for hospitalized patients where they estimated that each day patients lost 100 ml of fluid for each 100 calories they burned. This is where the rule of thumb that you need 1 ml of water for each calorie that you burn comes from (their actual model had a variation based on initial body weight as well). Assuming that the same relationship between fluid loss and calories burned exists for backpackers (I’m a bit dubious) you would estimate that for a typical day in which you burn 5000 calories, you would need a total of 5L of water. On the AT, at moderate temperatures, I consumed an average of 4L of water a day (2L while hiking, 1L to rehydrate my dinner, and 1L in the evening/morning prior to hiking). If outside temperatures exceeded 80 degrees Fahrenheit I would typically drink 1 additional liter of water a day at lunchtime. My water consumption was typically less than that of my male counterparts on the trail who usually drank at least 1L of water/day more than I did. If you assume that athletes have a higher percentage of muscle (which is 70-75% water) and a lower percentage of body fat (which is ~10% water) compared to patients in the hospital, you might estimate higher fluid volume replacement requirements for athletes. Allowing for differences in body fat percentages, this might help account for some of the gender based variations in water replacement requirements that I observed as well.


 

 

Are there other ways that privilege and science influence your relationship with water and how much water you carry?

Backpacking Science and Privilege: Food

On long-distance backpacking trips we don’t take the same things for granted that we do at home and as a result we can gain some insights into our privilege and how it affects the way we hike our hikes, and pack our packs. In this series of three posts I’m going to talk about how science and privilege influence the way I pack my pack. Using science as my guide, I’m going to break the discussion into three parts (requirements for physiological homeostasis in the wilderness):

  1. Food: Our ability to regulate blood sugar levels (glycoregulation).
  2. Water: Our ability to regulate water and minerals (osmoregulation).
  3. Shelter/Heat: Our ability to regulate body temperature (thermoregulation).

Unpacking my Invisible Knapsack: Food

In 1989 Peggy McIntosh wrote a famous essay in which she likened privilege to “an invisible weightless knapsack of special provisions, maps, passports, codebooks, visas, clothes, tools and blank checks.” What follows is a list of food based privileges that hiking the trail has made me more aware of:

  • I don’t have to be hungry. Middle-class privilege means that this is usually true for me. On the trail, as long as I plan appropriately this remains true.
  • Being hungry won’t hurt me or interfere with my ability to function. I am hypoglycemic, so both on the trail and at home I need to be careful about what I eat.
  • I’ve never had to try to sleep with hunger gnawing at my stomach. Middle-class privilege means that this is usually true for me. On the trail, I run calorie deficits so large that this is no longer true… sooo hungry.
  • I know that if I need food other people will share their food with me. White privilege, middle-class privilege, and being a woman all probably contribute to the fact that this is a privilege I’m likely to get. On the AT this privilege becomes more obvious, and some people seem to rely on it.
  • As long as the food I eat is fit for humans it won’t make me sick. Food allergies and intolerances mean that this is not a privilege that I can always rely on.
  • I have enough body fat reserves to run a calorie deficit without compromising my short or long-term health. This is typically true for me. When I started the AT I was overweight and could definitely afford to run a calorie deficit and lose a lot of weight without compromising my health. As I head out to hike the PCT, I can’t rely on that nearly as much (see the science section below).
  • There are stores accessible to me where I can exchange money for food. Middle-class privilege means that this is typically true for me. On the trail, there are not always stores accessible to buy food when I am hungry. Access is limited by the remoteness of my location.
  • I know how much food and what kind of food I need to bring with me on a five-day backpacking trip. I have a lot of backpacking experience as well as access to resources that all allow me to have a good sense of what to pack for food and how to pack it.
  • What I eat, how much, and/or how often is not something people make comments about. I think that this should be true, but it isn’t. I thought gaining thin privilege would make this true, but it didn’t. Do you get this privilege?
  • My appearance and social standing are independent of my metabolism, what I eat, and how much I eat. On the trail this was true.
  • The research that I use to determine how much food I should eat is based on people who look like me. White privilege means that this is largely true, however, most of the data is based on men and not on women.
  • I don’t have to worry about where my next meal is coming from. Middle-class privilege means that this is usually true for me. On the trail, figuring where your resupplies are going to be and where your next meal comes from becomes more important.
  • I can afford the healthiest, lightest weight food available. Middle-class privilege.

Though all of the above are likely to influence the amount of food I pack and the type of foods I pack, there are some guidelines based on science that you can follow to help determine the minimum amount of food you should carry.

Packing My Pack: Food

The amount of food that you need to carry depends on the number of calories you are likely to burn during your trip. The military probably has some of the best research about calorie consumption while hiking (marching) over long distances on rugged terrain with a pack. They suggest that people engaged in prolonged physical activity (like backpacking) need to consume 4000-5000 calories per day and that those numbers are even higher for cold conditions. The numbers calculated for recreational backpackers (using the heart rate method of energy expenditure by Hill et al ) are similar to those determined by the military, suggesting that backpackers typically expend 5000 calories per day. Despite burning 5000 calories a day, most backpackers were only consuming about 2000 calories a day, which is consistent with what I observed among 2013 AT thru-hikers.

Why don’t backpackers carry more food? Food is heavy. Most trail food is 100-200 calories/ounce, so to get 5000 calories/day you need to carry between 1.56 and 3.13 lbs of food per day. Assuming an intermediate calorie density and assuming that you want to maintain your existing body weight, you should be carrying about 2 lbs of food per day. So, assuming a five-day interval between resupply options, you should carry about 10 lbs of food. If there is significant probability that you will encounter detours, delays, or want ad hoc flexibility to extend the amount of time between resupplies, you may want to pack extra calories.

If you have sufficient body fat reserves to healthily maintain a calorie deficit you can carry less weight in food. Most AT thru-hikers carried between 2000 and 3000 calories of food per day, which works out to be about 1 lb of food per day. On my AT thru-hike I ran a significant calorie deficit. I lost 50 lbs.  Assuming that each pound of lost body fat is equivalent to 3500 calories burned, that means that I ran a net calorie deficit of 175,000 calories. Since I was on the trail for roughly 150 days, that works out to an average calorie deficit of 1167 calories/day.

For my PCT hike, I can’t afford to run a calorie deficit that large. Based on my current weight I figure I can lose a total of 10 lbs (a net 35,000 calorie deficit) on my hike of the PCT without becoming unhealthy. Assuming that the trip takes 150 days (the same amount of time I was on the AT), I can run an average daily calorie deficit of 233 calories.

As our calorie deficits on the trail climbed we put more and more effort into maximizing the calorie density of the foods we carried. Though the range of calorie densities for trail food was typically 100-200 calories/ounce, we all started to add more calorie dense items to our resupplies as we got further into our hikes. Which foods are the most calorie dense? Fats! (Here’s a list of the most calorie dense foods). Fats have 8.8 calories/g or 246 calories/ounce, and so high fat foods become very popular on the trail. To get more fat into my diet I carried things like Justin’s Maple Almond Butter (190 calories per 32 g or 166 calories per ounce) and packets of olive oil (240 calories/ounce).

In addition to carrying more calorie dense foods, we tried to help make up for our on trail calorie deficits with calorie surpluses in town. Ice cream, pizza, oreos, doughnuts… all of the most calorie rich foods we could find we ate. Though fats are the most calorie dense foods, the runner up (Ethanol, at 7 calories/g or 196 calories/ounce) was incredibly popular in town. Using ethanol as your major source of calories has some significant downsides however, including (but not limited to) hangovers and dehydration. If you get dehydrated in town, you need to carry (or otherwise procure) more water on the trail and water is heavy (1 L is 1 kilogram, or 2.2 lbs)!

In the next post I’ll discuss how privilege and science influence the way that I deal with water on the trail.

 


 

Are there other ways that privilege and science influence your relationship with food and how much food you carry?