In one randomized controlled trial, a high sodium diet (300 mEq or 6.9 grams daily) was found to lower standing heart rate and increase blood and plasma volume when compared to a low sodium diet (10 mEq or 0.2 grams daily).[1] Thus, It is generally recommended that people with POTS consume roughly 2–3 liters of fluids and 3–10 grams of sodium daily (equivalent to about 1 to 3.5 tablespoons of table salt daily).[2]
One study showed that following a gluten-free diet alleviated some symptoms of POTS; however, more rigorous research is needed to confirm this.