user-1: I was wondering, in the case of a beginner in meditation, how much having eaten sugar might affect meditation quality? Also, I wonder what else -- in terms of states altering the mind like tiredness or sexual arousal -- might affect meditation quality. What are the things to avoid to preserve meditation quality?

user14789: The vinaya probably talks more about food. In the suttas the stock phrasing is ''moderation in eating'' is associated to good condition with minduflness, like that
https://www.buddha-vacana.org/sutta/anguttara/04/an04-037.html

"And how does a monk know moderation in eating? There is the case
  where a monk, considering it appropriately, takes his food not
  playfully, nor for intoxication, nor for putting on bulk, nor for
  beautification, but simply for the survival & continuance of this
  body, for ending its afflictions, for the support of the holy life,
  thinking, 'I will destroy old feelings [of hunger] & not create new
  feelings [from overeating]. Thus I will maintain myself, be blameless,
  & live in comfort.' This is how a monk knows moderation in eating.

https://www.buddha-vacana.org/formulae/bhojan.html

-1: <p>I was wondering, in the case of a beginner in meditation, <strong>how much having eaten sugar might affect meditation quality?</strong> Also, I wonder what else -- in terms of states altering the mind like tiredness or sexual arousal -- might affect meditation quality. <strong>What are the things to avoid to preserve meditation quality?</strong></p>
 14789: <p>The vinaya probably talks more about food. In the suttas the stock phrasing is ''moderation in eating'' is associated to good condition with minduflness, like that</p>

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<blockquote>
  <p>"And how does a monk know moderation in eating? There is the case
  where a monk, considering it appropriately, takes his food not
  playfully, nor for intoxication, nor for putting on bulk, nor for
  beautification, but simply for the survival &amp; continuance of this
  body, for ending its afflictions, for the support of the holy life,
  thinking, 'I will destroy old feelings [of hunger] &amp; not create new
  feelings [from overeating]. Thus I will maintain myself, be blameless,
  &amp; live in comfort.' This is how a monk knows moderation in eating.</p>
</blockquote>

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