What are the minimum calories to survive, short term and long term

I thought in WW2 some country, maybe the Netherlands, determined something like 1200-1500 calories a day was the minimum to survive.

I know for short term people can survive a few weeks w/o food, if heavy a few months. But after a few weeks/months of almost nothing to eat most fat people become skinny and there isn’t nearly as much tissue left to catabolize.

But what about long term like months or years, if all you want is for people to survive and function (not be happy and well adjusted)? If you underfeed them their bodies will reduice their fat levels, muscle levels and RMR which would probably result in equilibrium eventually to match the lower calories. 1500 calories a day doesn’t sound like a lot, but if someone is reduced to 120 pounds that is 12-13 calories per day. People above that level would lose a lot of weight, but eventually wouldn’t their metabolic needs drop so much that 1500 a day was sufficient?

So assuming an apocalypse and in order to keep as many people alive as possible, they shoot for the minimum calories what would those be? I’m assuming anywhere from 1000-2000 a day but don’t know.

Research on the remaining living survivors of the Siege of Leningrad seems to answer that it depends on what genes you possess. This from Science June 4, 2015. Over 1 million died but those who survived seemed to have genes that made more economical energy metabolism more possible.

1500 Calories a day is about what those who attempt calorie restriction as a potential means of life extension have attempted. It may not extend life span but it did not starve them to death either.

Of course they get to have high quality calories with adequate protein and micronutrients.

I have a few questions about that study.

Who were the 10% who didn’t lose weight on 200 calories a day?

Do they know why people developed diabetes in such high rates after a starvation diet? I know nowadays there is some speculation a starvation diet can (temporarily) reverse diabetes by reducing fat in the organs. But I think many people who did the Newcastle diet gained weight and diabetes back.

I’ve also heard that diabetes and obesity are possibly both side effects of a metabolism geared to survive famines. Obesity contributes to diabetes, but people whose metabolism is designed to survive famine are prone to both obesity and diabetes. I think the hypothesis was that insulin resistance helps ensure nutrients get to the proper organs and isn’t taken up by skeletal muscle. So is it possible the survivors were the ones whose metabolisms were geared towards diabetes anyway?

People can survive a season on 200 calories a day, but not a lifetime. I was thinking of the film ‘the Road’ and what the minimum caloric intake would be for long term survival (assuming mild manual labor).

Likely not all were eating the same amount. But yes, an interesting question since some maintained weight on at least very low calories, even if they got more than most.

And I posted an incorrect link. This is the correct one.

And of course those who survived may have included some who managed somehow to get more than the average calories.

The speculation is that those same genes that can cause a thriftier energy economy can increase the risk for diabetes.

The people on the TV show “Naked and Afraid” seem to be surviving on less than 100 calories a day on average. After 21 days they have lost lots of weight, but they managed not to starve to death.

Short term? 1500 calories a day is an absurdly high amount, if you’re trying to assess the bare-minimum needed to stay alive. Medical diets prescribed to morbidly obese patients generally run in the 500-800 calorie/day range. These diets are medically supervised, however. So I’d guess the bare minimum would be even lower than that.

Short term people can survive on 0 calories a day, but only for a few weeks (or if they are heavy, a few months).

However if you have an apocalypse scenario and food is rationed, what is the minimum for long term survival? I’m assuming 1000-1500. On that most people would probably drop to about 100-120 pounds which would give them 10-13 calories per pound. Assuming an increase in RMR efficiency due to the weight loss people could probably survive indefinitely on that, I assume.

Again however it likely also depends on the composition of the diet. An apocalypse scenario is unlikely to have rationing such that adequate protein and micronutrients are present … their lack rather than the calorie lack may turn out to be the limiting factors for survival.

OTOH experience with adaptations to low calorie (LCD) and very low calorie diet plans (VLCD) illustrate the compensations you seem to wonder about. VLCDs are defined as total diet replacements with <800 kcal and >400 to 450 kcal/d. 800 and 1200 kcal/d are classified as LCD. These do have adequate protein and micronutrients. By the 16 to 24 week mark subjects were losing the same total amount whether they had been in a LCD or a VLCD plan, the latter plans averaging 400 Cal/d less.

Of course we cannot know what compliance was however.

That said based on the information in that article weight loss at 800 calories a day or less and at 400 calories a day or less both seems to be about 2.0 kg in the first 4 to 6 weeks and decreases to about 0.8 kg over a 6-month period. Another 400 calories less does not make it worse but ongoing weight loss is nevertheless occurring at the 800 calorie a day level and not apparently coming into equilibrium despite loss of mass and decreased energy use per unit mass. So for long term higher than 800 but 400 apparently no worse than 800. (Unfortunate that they use one size fits all.)

Apparently the ratio of resting metabolic rate to lean body mass drops to roughly 82% of normal fairly quickly in a very low calorie circumstance and maintains there.

Since WWII experience was cited in OP, I just came across the following from The German Military Command in Occupied Poland:

2,600 calories per day for Germans
609 for Poles
503 for Jews. Later, the Jews’ number of allotted daily calories was reduced to 369.
The figures are cited here in a review of the book by Halik Kockanski, The Eagle Unbowed: Poland and Poles in the Second World War.

I recall seing a photo of the original document in which this law was passed down. (A cite to that is not in the review, but presumably in the book.)

I don’t see how that’s relevant.