I certainly don't want to offend anyone, but if it is asked in Isaiah 58 whether it is this manner of fasting that G-d has chose; when one starves oneself, practices self-denial, afflicting one's soul or answers for one's soul, and bows the head, spreading sackcloth and ashes, and so on.. what's the answer? Are such habits acceptable to G-d? Because it seems we have similar habits on Yom Kippur, while from from Isaiah 58:6 on [isn't this the fast that I've chosen?] it becomes clear that G-d might hold a different point of view when He talks about fasting, i.e. that it should be about breaking/loosing the chains of wickedness etc..
(Or should I translate the words in Isaiah 58:5 הכזה יהיה צום אבחרהו יום as "Such will be the fast I will choose, a day upon", and the words הלזה תקרא צום, ויום רצון ליהוה as "This will be called a fasting, a day acceptable to the Lord", in such a case the beginning of Isaiah 58:6 הלוא זה צום אבחרהו could be confirmatory "After all, this is the fast I will choose")