1) Sodium is an essential nutrient so you need to consume it regularly. The safe minimum sodium intake for individuals who do not sweat excessively is said to be 200 mg sodium (500 mg salt) per day.
Recommended Dietary Allowances: 10th Edition, 1989, minimum intake for salt:
In consideration of the wide variation of patterns of physical
activity and climatic exposure, a safe minimum intake might be set at
500 mg/day. Such an intake is substantially exceeded by usual diets in
the United States, even in the absence of added sodium chloride.
2) When sweating a lot, you may need more than 5 grams of sodium per day:
Sweat rate and sodium loss during work in the heat (PubMed, 2008):
People working in moderately hot conditions for 10 hours on average
will lose between 4.8 and 6 g of sodium (Na) equivalent to 12–15 g of
salt (NaCl) depending on acclimatisation.
3) What can help to prevent kidney stones?
According to Nutritional Management of Kidney Stones (Nephrolithiasis) (
Clinical Nutrition Research, 2015), these dietary measures can help reduce the risk of kidney stones:
- maintaining healthy weight (probably the strongest effect)
- sufficient water intake (~1.5-2 liters/day or more when sweating a lot)
- low sodium intake (2-3 g sodium/day)
- high potassium intake (>3 g/day; in fruits and vegetables)
- high calcium intake (at least 1 g/day)
- low intake of animal protein
- only moderate intake of vitamin C (<1 g/day; avoiding vitamin C supplements and fruit juices as a source of fluid)
- low oxalate intake - for oxalate stones (avoiding spinach, rhubarb, potatoes, nuts)
Diet does not likely cure the established kidney stones. A doctor can tell what is the optimal treatment for a given type and size of stones.
To answer more directly:
Can the body rely on some sodium reserves during the time it takes to get rid of the intruder (meaning no salt diet)?
You may go a week on a sodium-free diet, but possibly more or less, depending on the loss of salt with sweat: Salt craving: The psychobiology of pathogenic sodium intake, Physiology & Behavior, 2008:
The classic study by McCance in 1936 was among the first experimental
investigations of the effects of sodium deficiency in humans .
Using sodium-free diets and sweating, it took about 7 days to make subjects sodium deficient. The experiments were carried out over 11
days, therefore all of the effects reported were present within the 4
days of sodium deficiency. The participants reported that they
experienced extreme, unquenchable thirst.
Such a short zero-sodium diet would very unlikely have any meaningful effect on kidney stones; long-term zero-sodium diet is not compatible with life.
Is it better to take a minimum of salt daily?
(American Family Physician) recommends limiting sodium intake to 2 g/day (5 g salt/day).
Reducing sodium intake as a single dietary measure may have only little effect, so this may work better as a whole approach by also taking care about consuming enough potassium and calcium and avoiding excessive intake of animal protein and vitamin C.
So, such approach can be somewhat preventative, but the effect can differ a lot from person to person. This article covers the diet for common types of kidney stones.