Good question!

I just did a little research, and WOW! They pack the meals with sodium. I looked at a the Mountain House Chicken ala King first and it has 1120mg (insane amount) of sodium for 310 calories. As a reference, an entire MRE has an average of 1800mg of sodium for an average 1200 calories. That comes to a little more than 3mg of sodium to a single calorie in the Mountain House chicken ala king, and a little more than 1mg of sodium to 1 calorie in an MRE. Both MREs and Mountain House meals vary depending on the menu, but those are good indicators these are NOT good meals when water is scarce, especially not the Mountain House ones.

Mainstay rations bars are 23mg of sodium to 400 calories. That comes to 0.04mg of sodium to 1 calorie. Datrex rations have 0.75mg of sodium to 200 calories. Too small to bother with a ratio.

You must consider the amount of exertion you will be doing. If you are working hard and sweating, high sodium is a good thing. If you are waiting it out in an arid environment and not really doing much heavy physical activity with minimum water, sodium can kill you.

You can prepare for both by packing a sports drink powder high in potassium and sodium with your Mainstay or Datrex.

I pack the Gatorade G3 Recovery Powder. You can get it in individual 1 ounce packets single serving packets. They have a good amount of protein, carbs and electrolytes.