In relation to this question, I would like to know why Vayikra 16:31 says v'initem, often translated as afflicting, cause if afflicting is about fasting then why isn't the word tzom צום used if this was what was meant by 'the Author'.
Is it really about fasting or is fasting really included, what proof is there?
According to the Mishna (Yoma 8:1), Yom Hakkippurim is forbidden in eating, drinking, washing, anointing, wearing shoes, and marital relations. The Gemara (76b) tries to derive how each of these prohibitions is called "affliction" (עינוי). If the word וצמתם were used, it would not have expressed any of the prohibitions besides eating and drinking.
This answer addresses the question of why the word ועניתם is used instead of וצמתם, assuming that fasting is included, rather than proving that fasting is included.
Some users pointed out that this answer might be less compelling according to some opinions (the Rosh, which Heshy quoted from Tif'eret Yisra'el to the Mishna) who hold that the afflictions besides eating and drinking are not forbidden from the Torah.
The gemara discusses at length in Masechet Yoma 74b the commandment of "suffering" ועניתם.The gemera asks how do we know the Torah didn't mean that one should sit in the sun all day!
The gemara then enumerates a few baraytot that derive this law in various ways using exegesis. Some are based on the juxtaposition of this law with the prohibition against doing melacha on Yom Kippur, which is punishable by Karet.
Here are a few of the approaches there:
Doing melacha is a commandment to be passive, so too the suffering should come from being passive - not eating or drinking.
Melacha is punishable by Karet, so too the suffering must be connected to an action that involves Karet in another area of the Torah (the gemara there enumerates the different prohibitions of eating that involve Karet). The gemara then applies the rule of "riba hakatuv" which uses the unnecessary plural form to derive all foods, and not just those punishable by Karet.
The Torah warns that one who does not keep this commandment will be destroyed והאבדתי את הנפש ההיא. From this consequence, the Gemara derives that the prohibition must involve something that can potentially be life threatening - not eating or drinking.
There is a Gezera Shava גזירה שוה between ועיניתם and ויענך וירעיבך - being hungry.
There is much to add to this discussion, if you are interested in delving deeper into these derivations I suggest you study the Gemara there with its commentaries
