njuːtɹˈɪʃən sˈaɪəntɪsts bɪɡˈæn tə ɹᵻfˈaɪn ðɪs haɪpˈɑːθəsˌɪs ɪnðɪ ˈɜːli twˈɛntiəθ sˈɛntʃɚɹi, ˈɛmfɐsˌaɪzɪŋ ðə ɹˈoʊl ʌv nˈɛɡətˌɪvli tʃˈɑːɹdʒd pˈɑːɹɾɪkəlz ˈænaɪənz ænd pˈɑːzᵻtˌɪvli tʃˈɑːɹdʒd pˈɑːɹɾɪkəlz kˈæɾaɪənz ɪn fˈuːd.
Nutrition scientists began to refine this hypothesis in the early 20th century, emphasizing the role of negatively charged particles (anions) and positively charged particles (cations) in food.