General food needs - calories, vitamins, salt
The basic need you have on most trips is energy. After that a little salt may be required, but not a lot. That said, if you are accustomed to overloading on salt in your ordinary diet (and most people are), you may find it takes a little while to get used
General food needs - calories, vitamins, salt
The basic need you have on most trips is energy. After that a little salt may be required, but not a lot. That said, if you are accustomed to overloading on salt in your ordinary diet (and most people are), you may find it takes a little while to get used to a low-salt diet. Unless you are on a trip lasting far more than a week, vitamin deficiencies are just not going to happen. However, too much bland tasteless food can be dead boring, so some ingenuity is needed to keep everyone happy and well fed. This is where having a regular walking partner is very convenient: you know what that person likes - and dislikes.
For technical details of what you need we have the following quote from the Outdoor Action Program, Princeton University, accuracy unknown.
Food
Planning food for winter activities must take into account the great demands the cold weather and physical activity placed on the body along with the difficulty of preparing foods in the winter (it takes time, stove fuel) and having a menu which appeals to the group). Appetite is generally reduced during winter activity even through the food needs of the body have increased. If the meal isn't appealing, it won't get eaten. In some situations you literally need to force yourself to eat. [Happens above 6000 metres sometimes. RNC]
Food types
All foods are made up of varying proportions of the three basic food types - carbohydrates, fats, proteins, and water, vitamins and minerals. Each of the three major types can be converted into simple sugars and burned by the body to produce energy but the time required for conversion increases as the complexity of the molecule increases, so carbohydrates are quicker to convert than proteins and proteins quicker than fats.
| Dietary Percentage for Winter Camping | Food Type | Nickname | Description |
|---|---|---|---|
| 50% | Simple Sugars | kindling | 5 calories/gram (1,800 cal./lb.) - released quickly. |
| Complex Carbohydrates | sticks | 5 calories/gram (1,800 cal/lb.) - released quickly. They are easy to digest. Candy, cereal, bread, rice, macaroni, dried fruit, vegetables. | |
| 20% | Proteins | logs | 5 calories/gram (1,800 cal/lb.) - generally released slowly. Proteins are primarily used for maintenance and building of body tissue. Meat, fish, cheese, milk, eggs, nuts, grains. |
| 30% | Fats | logs | 9 calories/gram (4,100 cal/lb.) - released very slowly but are useful because they release heat over a long period. However, it takes more energy and more water to break down fats into glucose. Margarine, nuts, cheese, eggs, and fats from pepperoni, salami. |
Vitamins and Minerals
These are generally found in most foods we eat and for a trip less than 7-10 days no special resources are needed. For longer trips and expeditions vitamin and mineral supplements are necessary. See a physician to get specific recommendations for expeditions.
Caloric Requirements
General caloric requirements increase in the winter due to the energy expended in keeping the body warm. This much is obvious. What is less obvious is that larger people need more food than smaller people to keep going at the same rate. There have been may expeditions where this has become painfully obvious over time, with Antarctic ones being especially prominent. Time and again, they found that it was the big men who collapsed from malnutrition when everyone was getting exactly the same ration. We all know that a little compact car burns less fuel than a big V8 SUV: why should people be any different? But 'equal shares' seems 'fairer' if you don't think about real physiology.
Caloric requirements for different activity levels are summarized below, with full ackowledgements to Rick Curtis, Outdoor Action Program, Princeton University. I dare say other tables of figures exist, and may even differ slightly. The figures do not allow for variations on body mass either. What matters most here is the range spanned, depending on what exercise is being done.
| Activity | Caloric Requirement (kg-cal/day) |
| Basal metabolism | 1,500 calories |
| Sedentary occupation | 2,500 - 3,000 calories |
| Three season backpacking | 3,500 - 4,000 calories |
| Winter backpacking | 4,500 - 5,000+ calories |
| Pulling a 450 lb sled across Antartica | 10,000+ calories |
[The last figure comes from 'Mind over Matter', by Rannulph Fiennes. He hadn't included that much food in his planning. They didn't have enough warm clothing, and used a lot of energy just staying warm. They nearly died of starvation, and lost huge amounts of weight: fat and muscle. Their choice, not mine. I have to say that while the guy is obviously very tough and determined, his knowledge of gear and planning is woefully inadequate. A subsequent trip over part of the same route by another group had far less drama, but they were much better equipped. RNC]
Weight of dry food per day
So how does the above translate into the weight of food required per day? Well, for a start, this depends greatly on what sort of food you are carrying. Fresh meat and veg? Heavy! But if you do the normal bushwalking thing and carry dry food, we can give some typical figures. They illustrate the effect of the (winter) weather and also of a long hard fast trip (35 km/day in cold weather). There is also one at the end which I feel is very atypical, but note that the author of that one lost a lot of weight on the trip. Such weight loss cannot be sustained safely. Contributions from you would of course be welcome.
| Person | Body wt | Season | g/day | Comments |
|---|---|---|---|---|
| Author | 64 kg | 3-season | 640 | 8 day trip |
| Wife | 54 kg | 500 | ||
| Author | 64 kg | Winter | 770 | ski touring |
| Wife | 54 kg | 650 | ||
| Author | 64 kg | 3-season | 1000 | at end of long, hard and very fast trip |
| Wife | 54 kg | 850 | ||
| Michel | 70 kg | 3 season | 255 | but he lost 5 kg |
Rate of Digestion
So that tells you how much you need to eat, but does not tell you how soon you can draw on the energy. Clearly, a diet of celery and mushrooms might be ... interesting?
Simple sugars such as glucose may be absorbed into the bloodstream almost immediately. These molecules are small enough to pass through cells and into the blood in a matter of minutes, and may even do so while food is still in the mouth by zooming through cells in the cheeks and gums.
Most food needs processing, however, before it can pass into the bloodstream. This starts from the moment that it enters the mouth. Here it is crushed to bits until it is small enough to be swallowed, and enzymes are released that begin to break it down further.
Once it starts its journey down the throat, food reaches the stomach very quickly, but then sits there for about 2 hours. The stomach is where most food is broken down: physically, by the churning motions created by muscles in the stomach wall, and chemically, by enzymes, acids and other gastric juices. The resulting semi-liquid mush passes into the small intestine, from where it is absorbed into the bloodstream. The components that cannot be digested at all, such as dietary fibre, will move along slowly until they reach the large intestine around 6 hours later. Once they arrive there, any water still in them is absorbed so that only the indigestible materials remain. It may take up to 33 hours before they are finally expelled from the body as faeces.
After the swift initial digestion of simple sugars, proteins follow in about 4 to 6 hours, followed by various fats, which can take 6 hours or more to break down. Digestion time may vary depending on a number of factors, such as how long the food was chewed, and the age, health and size of the person eating it.
Some components of food, such as fibre, are hardly broken down at all and pass out of the anus relatively untouched. This includes compounds that contain lignin fibres from mushrooms and other foods, and cellulose from celery.
