AppleSkin, a mod that simply provides an overlay of the saturation mechanic on the hunger bar. By default it highlights the drumsticks with a yellow outline. I have already messaged the developer of the mod and requested the ability to move the overlay and with a bit more work on the users side it may be possible to use resource packs to tweak the appearance to fit with the aesthetics of the RPG HUD. Though I also feel that, with the mod being licensed under the "Public Domain", there would be potential for you to incorporate that functionality into the HUD much more seamlessly.

As a starting point, it should be possible to add AppleSkin compatibility by making RPG-Hud fire the relevant Forge events when it's drawing the vanilla version of the hunger bar, as that's what AppleSkin listens for (RenderGameOverlayEvent.Pre and RenderGameOverlayEvent.Post with type RenderGameOverlayEvent.ElementType.FOOD):

https://github.com/squeek502/AppleSkin/blob/1.10.2/java/squeek/appleskin/client/HUDOverlayHandler.java

See also net.minecraftforge.client.GuiIngameForge for when Forge normally fires these events, which rendering contexts are used, etc.