Why is refeeding slowly necessary after a long term fast?


Why is refeeding slowly necessary after a long term fast?

In: 152

Non-eli5: https://www.medicalnewstoday.com/articles/322120

Basically, after a period of time with little or no food intake, your body switches how it processes energy stores. First it’ll start using up stored fats, then it’ll move to muscle tissue and other proteins. The amount of vitamins and essential electrolytes in your body will fall too, as they aren’t being replenished.

When you start eating again, your body switches back to how it processes energy before, but this creates a sudden spike in your blood sugar (bad) followed by a spike in your insulin (also bad), which will lead to further electrolyte imbalances. This has a knock-on effect on your organs and bodily systems, which can be fatal.

It’s important to have professionals go through the refeeding process to ensure that you’re receiving the proper electrolytes in order to process the food you’re receiving (and to ensure you’re not eating too much too quickly).

The big problem has to do with how your body stores and uses energy. It uses phosphates, in the form of a molecule called ATP, to supply the energy for the things your cells do. But it also uses the phosphate to store nutrients in cells. After a long fast, your body is depleted of both nutrients and phosphate. If you refeed quickly, your body will try to use and store all those nutrients quickly, which sucks up all the phosphate, so it can’t be used to make ATP. Without ATP, your body doesn’t have the energy it needs to do things (notably breathing). There are other things going on, such as electrolyte issues, as the other answer says

We discovered this empirically when Holocaust survivors were brought back to Britain. Aside from the expected trouble with handling food and throwing up, many suddenly died around day 3 from what we now call refeeding hypophosphatemia (low blood phosphorus); it may be mostly due to insulin from sudden carb intake or a rise in calcium. It is not like we do controlled experiments to figure it out.

There are a host of other issues as mentioned below, mostly vitamin deficiencies.

There are protocols for doing refeeding, but it is pretty hard to actually need these (refugee camps, anorexia nervosa).

It was a real WTF moment for the Brits, and how sad to survive a concentration camp only to die on free soil.

Others have given more detailed explanation but in short you’re body doesn’t like sudden changes. This is on more than just food.