Hunger strikes can go on for weeks, but each day a person goes without normal nourishment places further strain on the intricate and finely tuned body organs and systems that keep a person alive.
Dr. Gwynne Jones, a critical care physician in Ottawa who has not treated or examined Spence, told CBC Radio's Ontario Today that any effects on body tissue will extend beyond fat stores. Muscle and lean body mass, "the bits of the body that do the actual work," Jones says, are also being broken down.
Today marks the 25th day of the hunger strike that Spence, the chief from Attawapiskat, in northern Ontario, launched in a bid to get a meeting of First Nations leaders, Prime Minister Stephen Harper and Gov. Gen. David Johnston.
Harper announced earlier today that he would meet with First Nations leaders on Jan. 11.
Basic caloric requirements
The average person needs about 1,200 calores a day to keep organs functioning, the brain active, the heart beating and basic growth functions going, says registered dietitian Jennifer Sygo of Cleveland Clinic Canada in Toronto.
"It certainly depends on age, gender, amount of muscle a person has … their size. Bigger people tend to have higher metabolisms than smaller people," she says.
Beyond that basic caloric requirement, you need another 30 per cent to look after the activities of daily living — everything from brushing your teeth to walking around.
Since the strike started on Dec. 11, Spence has been taking fish broth and tea.
"Her condition continues to weaken every hour," read a statement released by the Attiwapiskat First Nation last week.
Jones says the fish oil in the broth "will give her some benefits" because it will contain some essential fatty acids that maintain the function of the intestine a little bit better. At the same time though, he says, muscle and lean body tissue, which are fundamental for energy production and immunity, will be breaking down.
A diet of fish broth and tea doesn't come close to meeting a person's nutritional needs for even the most basic body functions. And if a person isn't meeting the basic needs through food, the body looks elsewhere — that is, inside itself — for energy.
"The human body is well-suited to be able to manage that for a short period of time," says Sygo.
"We can liberate fat stores ... the fat that we naturally have around our organs, the fat we have under our skin, those are useful stores because we are built to be able to handle feast and famine to a certain degree."
But that comes at a cost to well-being over time. With no glucose coming in, the body launches into a state called ketosis.
"In effect, what that is, is converting fats into a sugar-type byproduct that the body can use for basic fuel because glucose is what fuels our brain and it's what fuels any type of quick activity, if we had to run away from a fire or something like that," says Sygo.
The body converts the fats into basic units of energy called ketones, a process that, among other things, can lead to bad breath.
"One of the ketones that is naturally produced by the body is called acetone, and if you know the smell of nail polish remover you have an idea of what acetone smells like," says Sygo.
That could happen within a couple of days of beginning a hunger strike.
Some people, Sygo says, willingly enter a ketotic state for weight control, and there are people who talk about successfully managing their health through ketosis.
"Obviously medically that's really debatable, but the point is [Spence] isn't necessarily in danger in the early stage. She may not feel well. She may feel foggy mentally, certainly not have a lot of energy," says Sygo.
"This would not be a good time to run a race, enter any athletic competition, all of which requires glucose for successful performance."
How long a person can subsist on the limited intake of a hunger striker can't be predicted and depends on many factors, including the person's physical condition at the beginning of the strike.
"Their nutrient status to begin with would have a significant role to play. If they were well-nourished and in good health they could sustain it longer," says Sygo.
Hunger strikers over the years have had various approaches to their actions. IRA prisoner Bobby Sands took salt and water before his death 66 days after beginning his strike in 1981. Nasrin Sotoudeh, an imprisoned Iranian human rights lawyer, drank water mixed with salts and sugars before ending a 49-day hunger strike last month, the New York Times reported.
Fluids are critical to maintaining life. In general terms, the human body can go without water for two to three days. A lack of fluid causes problems with kidney function within just a few days, particularly if a person is active.
Inside the body of someone on a hunger strike, many other changes will occur over time.
"You could become anemic," Dr. Ewan Affleck told CBC News in Yellowknife.
Chronic diarrhea is possible because the bowel loses its ability to function through a lack of essential minerals and nutrients needed for digestion.
Signs of deficiency, particularly of protein, could emerge throughout the body.
"Over time you might start to see things like the skin becoming more brittle and eventually you might see red sores or cracking of the skin, especially around the hands," says Sygo.
"Hair might start to break. Nails might start to break. Those would all be signs of protein deficiency as well as other nutrients that would be associated with protein like zinc."
If a person chooses to end a hunger strike, it's not simply a matter of deciding to eat a big steak dinner in celebration — in fact, doing that could pose a significant danger to a body that has become accustomed to virtually no nutritional intake and which is lacking the necessary enzymes in the gut for digestion.
"You start very gradually," says Sygo.
Often, that could begin through intravenous feeding.
Affleck says there is a risk of permanent damage from a hunger strike in the long run.
In extreme cases, there could be permanent organ damage. However, says Affleck, "the body is resilient."
Also on HuffPost