Lemon juice, apple cider vinegar, sour whey, Swedish bitters and kombucha are all invaluable aids to improving digestion. Try each of them to find which works best for you.
Mix a teaspoon, or a few teaspoons of fresh lemon (or lime) juice in a glass of water, and drink it 20 minutes before a meal, or at any time. It helps with the digestion of food (good to take before a meal) and a wide range of digestive problems, and contributes to general health and longevity.
You can also use lemon juice and ACV on your skin. The acidity is beneficial, promoting acidic bacteria and inhibiting fungi. The acidity also inhibits demodex mites living in hair follicles and oil glands. Almost every adult has these mites, but in some people their population gets out of control, or their skin reacts to the mites.