‘In those days I Daniel was mourning three whole weeks. I ate no pleasant bread, nor did flesh or wine come in my mouth, nor did I anoint myself at all until three whole weeks were fulfilled.'
We are not told why Daniel was mourning. Perhaps news had reached him of the dire straits of the exiles who had returned to Jerusalem at the instigation of Cyrus, or perhaps he was mourning over the significance of the visions that he had received, praying for God's mercy on those to be involved. But the seriousness of his mourning comes out in that it lasted ‘three whole week' (‘three weeks, days'). The days is added to demonstrate that the three weeks was to be taken literally (‘three weeks' could usually signify one and a bit to three weeks).
During that time he only drank water and had plain fare. And he refrained from the usual preparations for meeting people. (The emphasis on what he avoided counts against him having no food at all).