[Retrofitted]

From Scientific American: “This saying has been traced to a 1574 dictionary by John Withals, which noted that “fasting is a great remedy of fever.” The belief is that eating food may help the body generate warmth during a ‘cold’ and that avoiding food may help it cool down when overheated”. So it sounds like your Grandma was passing down the wisdom as it was originally meant!

https://www.scientificamerican.com/article/fact-or-fiction-feed-a-cold/#:~:text=This%20saying%20has%20been%20traced,it%20cool%20down%20when%20overheated.

[BDParrish]

She was thinking fasting was therapeutic for both. Thanks for the link!