How to set the hint_text to stay always on the top? - kivy

Question

I would like to have an MDTextField, whose hint_text stays always in the top of it, even if it's not focused or they are no letter written on it, but I don´t know how nor if it is possible.
code:
from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.core.window import Window
from kivymd.uix.screen import MDScreen
Window.size = (300, 500)
navigation_helper = """
<CalculatorScreen>
name: 'calculator_screen'
MDBoxLayout:
orientation: 'vertical'
padding: (0, "70dp" , 0, 0)
pos_hint: {"top": 1}
spacing: "5dp"
MDBoxLayout:
id: food_block
padding : ("5dp",0,"5dp",0)
size_hint: (1,None)
height: "33dp"
padding: ("2dp",0,"2dp","-20dp")
MDTextField:
id: kcal_result
hint_text: "Kcal"
size_hint: (0.14,None)
height: "30dp"
MDTextField:
id: proteins_result
hint_text: "Proteínas"
readonly: True
size_hint: (0.185,None)
height: "30dp"
MDTextField:
id: carbohydrates_result
hint_text: "Glúcidos"
readonly: True
size_hint: (0.175,None)
height: "30dp"
MDTextField:
id: lipids_result
hint_text: "Grasas"
readonly: True
size_hint: (0.15,None)
height: "30dp"
MDTextField:
id: sugar_result
hint_text_font_size: "5dp"
hint_text: "Azúcar"
readonly: True
size_hint: (0.15,None)
height: "30dp"
MDTextField:
id: salt_result
hint_text : "Sal"
readonly: False
size_hint: (0.10,None)
height: "30dp"
<MainScreen>:
name: "main_screen"
BoxLayout:
orientation: 'vertical'
MDTopAppBar:
id: title_bar
title: 'Dietas'
md_bg_color: 0.08,0.07,0.45
specific_text_color: 1,1,1
left_action_items: [["menu", lambda x: nav_drawer.set_state('toggle')]]
Widget:
MDNavigationLayout:
ScreenManager:
id: scr
CalculatorScreen:
MDNavigationDrawer:
id: nav_drawer
BoxLayout:
orientation: 'vertical'
spacing: '8dp'
ScrollView:
MDList:
OneLineListItem:
text: "Calcular comida"
on_press:
scr.current= 'calculator_screen'
title_bar.title = "Calculadora Comida"
nav_drawer.set_state('close')
MainScreen:
"""
class CalculatorScreen(MDScreen):
pass
class MainScreen(MDScreen):
def disable_top_bar2(self):
self.ids.title_bar.disabled = True
def enable_top_bar(self):
self.ids.title_bar.disabled = False
class DemoApp(MDApp):
def build(self):
self.theme_cls.theme_style = ("Dark")
screen = Builder.load_string(navigation_helper)
return screen
DemoApp().run()
I tried to set a hint_text on_text but didn't work (it appears only when clicked, remained there after deleting text, and stayed big in the top)