The sense is either,
1. Whilst their greedy appetite yet continued, and was not fully satisfied, before, they began to loathe it, as they did afterwards, Numbers 11:20. Or,
2. Before they were deprived or destitute of their desired food, whim they enjoyed it, and were still feeding upon it, as the next clause explains this. God's patience did not wait upon them till that food was spent, but fell upon them instantly.