The Fat Advantage

Two men from the same sunken cruise ship manage to float in their PFDs over several days and nights onto a barren tiny atoll somewhere in the middle of the vast South Pacific ocean. No food (no nearby flora or fauna), no pole, no string and plenty of water, and only one shady palm tree. One man, Jack, is of "ideal weight, While Jim who is of the same height, age, genetic heritage, is 50 pounds overweight. More specifically, Jack is Jim’s identical twin.

Would Jim have lasted longer in the ocean if they missed the atoll
Would Jim have lasted longer on the atoll

Jim and Jack are both going to die of hypothermia after “several days and nights” floating in the ocean.


Overall, a fat person will last longer in water, due to having fat insulation to guard against heat loss.

And will survive starvation longer, due to having more energy reserve stored in fat.

The ideal weight man will have better odds to overpower the fat man than the reverse. After that, he will have plenty of calories available, assuming he can use the salt water to preserve them. If by chance the reverse happened, the fat man would not survive as long with the skinny man as a food source due to his higher metabolic expenditure.

There are places in the world where the sea water is warm enough that you won’t die of hypothermia. Particularly if you’ve got some natural insulation.

The o.p, specifies “a barren tiny atoll somewhere in the middle of the vast South Pacific ocean”, so we can assume mid-ocean temperatures rather than shallow ocean temps you might find in the Caribbean or Mediterranean. At temperatures at or below 20 °C, survival time is at most about 8 hours, and even up to 30 °C you are going to experience a net loss of core temperature, especially if you aren’t eating. The “natural insulation” of subcutaneous fat is not insignificant in terms of initial cold water exposure but it just slows the cooling process; once the core temperature starts dropping below 35 °C you are going to start experiencing the effects of hypothermia. A wet suit would offer substantially more protection (and with cold weather immersion gear you can survive for many hours even in frigid water) but the scenario of the o.p. is a couple of passengers on a sunken cruise ship, so I’m assuming normal clothing that offers essentially no insulation and their PFDs.


How do you explain the USS Indianapolis then? About a third of the men who didn’t go down with the ship were alive 4 days later. Is the difference that this was the shallower Phillipine Sea as opposed to the Pacific Ocean? If so, I’d assume the OP was imagining the sinking of the Indianapolis as his inspiration and just had the location wrong.

If push comes to stab, the fat man will sustain the skinny man for far longer than the skinny man will sustain the fat man.

Looking at surface temperatures in the Philippine Sea they vary between 20 °C to over 30 °C. The USS Indianapolis was sunk on 30 July 1945, so presumably during the warmer part of the year. A cursory reading of the incident indicates that only 316 of the estimated 900 men who survived the initial sinking, succumbing to various causes including dehydration, desquamation and hypermatremia, hypothermia, and shark attacks but no breakdown of the estimates of each proximate cause.

So, assuming Jack and Jim make it alive to the island…in theory the overweight of the two will survive longer without food, but it isn’t as if subcutaneous fat is good as a completely replacement for intake of calories from food. Assuming adipocytes are 3,500 calories per pound, you might expect that the 50 pounds of fat would provide over 90 days of sustenance above and beyond what the skinny guy would survive. The reality is that subcutaneous fat mostly provides energy for anaerobic activity, and produces a lot of toxins that have to be filtered out during neoglucogenesis (metabolic synthesis of glucose). In starvation mode, the body tends to break down muscle and connective tissue for protein rather than synthesize it from fats, so that really becomes the limiting factor in starvation, not counting for micronutrient deficiencies such as dietary salts (sodium, potassium, calcium, magnesium) that result in electrolyte imbalance. In practice, people tend to die within 60 days of no nutrition regardless of initial body composition, with an outside figure of about 75 days, generally because of renal failure or the aforementioned electrolyte imbalances that result in cardiac and neurological problems.

The cannibalism idea isn’t so hot, either. In tropical conditions you won’t be able to preserve even lean meat with a salt water brine, and of course all the saturated fat will go rancid in a couple of days, notwithstanding the potential of transmissible pathogens in uncooked flesh. You’d be better off teaming up to get shellfish and maybe make primitive netting out of the PFDs and any surplus clothing to try to capture crabs. I’m not sure where all the fresh water is coming from on this tiny atoll but you should look for the source because it is where birds and any other edible creatures will go, and it is possible you’ll find edible fungus or insects.

Of course, if there is no conceivable hope of rescue (your guys didn’t grab an EPIRB and the boat didn’t send emergency signals or deploy a rescue beacon), maybe you should consider options to the misery of slowly starving to death and just take a deep dive with a heavy rock tied around your ankle.


If we’re going to start quibbling, it doesn’t matter who ends up as food, they will start to rot long before you could eat the whole thing, so they’re functionally the same amounts of food.

Now, if you had the equivalent weight of small children to work with, you could extend their shelf life by killing them in sequence.

The reality series “Alone” definitely demonstrates that principle.

Quick sidebar on the whole rotting thing - this question came to mind: I believe microbes are fairly local (which explains why sourdough bread from San Francisco is unique in flavor). But a small atoll in the middle of an ocean - would there be a lot of microbes present in such a remote location to advance decay at the same rate as a mainland location? Or, maybe the necessary microbes for rotting meat are already present on the people?

Their PFDs included wetsuits. They didn’t die of hypothermia. Back to the actual topic.

Anaerobic bacteria in the digestive tract are primarily responsible for the internal decomposition of bodies. MRSA and other topical bacteria will attack the dermis and mucosal tissues. There are, of course, free-floating bacteria everywhere there is any multicellular life, although it would take some time for a sufficient quantity to build up and attack a body. Even in lieu of bacteria, fats in the body will undergo autooxidation and become rancid, especially in direct sunlight.

Yeasts (fungal organisms) are responsible for fermentation in bread and spread by airborne spores, and require carbohydrates to grow and produce more spores. A desert atoll with no fruiting plants may be virtually absent of any yeasts.

The o.p. did not specify wetsuits, which are not a common part of marine safety equipment on cruise ships, and the question of whether they would survive longer in the ocean than on the atoll is an explicit question in the o.p.:


Thank you! That is informative.