I don’t think zero body fat is something anyone gets to. I saw a documentary a few years ago about a body builder for those posing shows. He would get to 2-3% fat coming up to a show by pretty much only eating tins of tuna, and he looked creepy.
WAG but, while a fat person may take longer to starve, they don’t have any extra water stored in their body so they will die of thirst long long before they starve to death.
I don’t think gluconeogenesis works on fats. You can metabolize fat to ketones and use ketones for energy, but the brain demands glucose. On an all fat diet you’ll constantly be losing muscle mass as you convert muscle to glucose to survive.
Without sidetracking the thread too much into a discussion of metabolism, I don’t think it is correct to imply that fats are substrates for gluconeogenesis in humans.
In short, for the most part carbohydrates to fats is an unfortunate one-way street in people. From an energy standpoint, this is an issue mostly for the brain, which really really likes glucose for its energy substrate.
To the OP:
A person with significant fat stores would last longer, on average, than a person without them. There are other factors at play. An ideal candidate would be a fairly healthy fat guy with plenty of muscle.
On review: What Bill said.
It’s older than a couple of hundred years; the word “paunch” has medieval origins going back to Latin. As long as people have had access to carb-rich diets (and especially alcohol), they’ve had the human equivalent of camel humps.
How many people starve to death in Western countries? There is one famous case , Chris McCandeless of Into The Wild.
I’ve never read anything to indicate that larger people (whether or not their mass is fat or muscle) don’t survive longer in general when it comes to starvation or harsh conditions. This is probably the reason research has showed that ‘overweight’ people live longer, on average, than those in the ‘ideal’ BMI range - if they have the misfortune to become terminally ill or injured, they have an advantage in having more bodily stores.
Keep in mind that death from starvation and malnutrition are not the same. Fat people could easily die from various forms of malnutrition and deficiences while still maintaning high body fat.
However, excess body fat is a disorder of the metabolism, nothing to do with storing surplus energy for famine. Species do not become fat when there is a food surplus (although they become fat for other reasons governed by hormonal balance, such as hibernation), they multiply. Unless the food they are eating promotes the metabolic changes that lead to obesity, as is the problem with our unnatural (in terms of the human animal for the majority of our evolution) modern diet, and was a persistant problem with zoo animals (leading to the common modern human problems such as obesity, heart disease, diabetes, and infertility) until an effort was made to provide each with a diet that closely mimics what they eat in their natural habitat.
I have a BMI of 16 with a normal body fat percentage (19%). Obviously I would be ‘fat’, not in terms of BMI but in body fat percentage, at a much lower total poundage than the vast majority of people. I am sure I would die much more quickly in the absence of food than average size or large people, as well, since I have so little total soft tissue to live off of, as well as having a very high requirement for daily calories to maintain my current weight (2200 to 3200 daily, and I’m only moderately active).
Right now? I dunno. Not many. A century and a half ago, plenty. Half a century ago, still quite a few.
Actually, rubarbarbin, it’s not true that fat people live longer on average than thinner people. Thinner people live longer, although it’s not a large difference. It’s only a few months longer lifespan on average.
The reason is that there are advantages going both ways. Carrying around extra weight is not good for the heart, so most of the advantage there is to thinner people. For some other causes of death though, there is some advantage to being heavier. On balance, it’s better not to be overweight.
When David Blaine did his little starvation-in-a-glass-box stunt, he fattened himself up considerably before beginning. It seemed to help.
Aren’t a lot of people in vegetative states eventually ‘let go’ by having their feeding tube removed?
New Scientist has an aside about it this week. They said that the limiting factor is actually the amount of available b vitamins. On a water and and vitamin diet, you could live 'til the body fat runs out. But without b vitamins, the body fat can’t be converted.
So has that fat guy on Lost shed any weight yet? Or did they find the inter-dimensional Krispy Kreme in the island’s wormhole?
With just water and literally zero food the physical stress of pure starvation can easily kill a significantly obese person well before all fat stores are completely used up. If you have some minor amount of food it’s easier to glide down to near zero fat like concentration camp survivors.
Yes but that requires protein, which is not stored like fat and is a limit as to how much stored fat one can use before dieing.
So it is needed to consume some carbs and or protein to preserve protein.
See above, protein is required to manufacture carbs from fat, eating nothing means the body will cannibalize itself to get enough carbs, so a fat person will not survive longer. But if there is some food such as insects, then the person should have enough dietary protein to prevent cannibalization - which is a advantage for a fat person.
Cite?
rubarbarbin, here’s the best citation I’ve been able to find with a quick search:
http://www.usatoday.com/news/health/weightloss/2009-08-25-obesity-lifespan_N.htm
Being overweight by less than 30 pounds reduces lifespan on average by a few months. Being overweight by 30 pounds or somewhat more reduces lifespan on average by about a year. Being overweight by 80 pounds or so reduces lifespan average by at least three years. The more you’re overweight by more than 80 pounds, the shorter the average lifespan you can expect.
Could someone who’s a doctor give us a better citation?
I’ve sometimes thought that if I ever met a genetically-engineered supersoldier who sneeringly asked me what my genes were good for, I could reply “surviving recurrent periods of famine”.