Possible Clues:

• An element of NHS meal provision
• ... Italian port's hesitation, which Davy did
• Whitish metal
• Metal in witherite
• Ba! I and you might make a meal of it if there's yeast around
• Substance swallowed to facilitate X-ray
• Element of meal — except one taken with hesitation
• Content of meal taken before X-ray
• Possible content of meal, bit of beef with a drink I consumed
• Element whose name is derived from the Greek for “heavy”