Foo combining is the term for an unproven nutritional approach that focuses less upon the quantity and kind of food consumed, and more upon the timing of their consumption. For example, advocates sometimes recommend that carbohydrates and citrus fruits should not be consumed at the same meal, claiming that the enzyme that digests carbohydrates (amylase) can only function in an alkaline environment. Similarly, when proteins are consumed, the stomach releases pepsin, which is its enzyme for digesting protein foods. Alkaline and pepsin neutralize each other when in the stomach together, thus rendering the digestive juices less effective in breaking down foods that have been miscombined.