How much fat would you need to survive in a long term situation?
I started seriously thinking about this after watching the show Alone season 3 in which the contestants strive to be the last one to stay in the wilderness for half a million dollars.
The winner stayed 87 days because the other remaining person was pulled out by the medics for losing too much weight (dropping below a BMI of 17). Zachary Fowler caught about 58 fish, one bird, and a handful of grubs in those 87 days.
That amounts to about 23,000 – 35,000 calories or ∼350 kcal per day (usd.gov).
A 25 y/o male that weighs 165 lbs and is 5′ 10″ tall would need to eat ∼2,750 calories per day to maintain his weight.
The food he gathered would maintain his weight for 8 – 12 days only, his fat provided the rest.
How fat should I be to survive 4 months eating 350 kcal per day?
Overweight but not obese!
I would have to weigh 200 lbs and would end up weighing 118 lbs with a BMI of 17 after 120 days.
I would need 35 lbs of extra fat.
Both the weight loss rate and energy needs change over time:
How many days would I last if I started with my current weight?
Only 2 months. Still that is much more than the 3 weeks rule of thumb that most survivalists memorize (rule of threes).
Where does that energy come from?
A sedentary 155 lbs man has ∼33 lbs of fat and ∼13 lbs of muscle as emergency energy source (Wilderness Medicine).
That is∼140,000 calories from fat and∼24,000 calories from muscle.
Those 164,000 calories could sustain you up to 2 months if you managed to get water, vitamins and minerals from the wild.
This is the reason why almost everyone can survive 3 weeks without food. And that’s why anyone can claim to be a survival expert without actually being able to thrive in the wilderness.
The 4 month threshold is what separates the survivalists from the hunter-gatherers.
Which nutrients would you need to survive?
You should always be well hydrated in a long term survival situation. Water is the most important nutrient.
Getting micro nutrients is relatively easy: although most edible plants relatively low energy, they do contain a good amount of minerals and vitamins.
Is an important nutrient, and it is very abundant. Pine needles, juniper, berries, and plants in general contain lots of it.
Is another essential micro nutrient. It is not easy to find except in coastal areas. Some plants and their roots are a good source of it. Animals (particularly blood) are another potential source.
Is the most common deficiency in the world. Red meat (specially liver), seafood, birds, and insects are a good source of iron from the wild. Another good option is to cook in a cast iron skillet, for it increases the iron content of your food.
After my partner and I returned from our six months in the wild, she had a blood test done. Even though we were at a “normal” weight and had eaten relatively enough food: she had an iron deficiency. I encourage you to check my post How starvation affects survival to learn more about its effects.