Hello and good evening.
The possible relation between cummerbund and Kummerspeck did intrigue me. According to my dictionaries, the former goes back to Persian "kamar" (waist), having reached the English language via Hindi "kamarband" (ca loinband)
The latter actually means additional fat because of worry, more often than not "Liebeskummer" (lovesickness). So you put on weight with man/woman problems, acchieving the exact opposite of what you desperately need.
"Kummer" derives from Middle High German "kumber" (waste, debris; trouble, stress, grief) and was borrowed from Middle Latin "cumbrus" (entanglement, dam).
It is related to "kümmerlich" (poor, miserable) and "Kümmerling" (weakling).
In some German regions "Kümmerling" also names a bitter "Schnaps". I suspect what people actually mean is "Kümmel" (caraway seed or cumin), as the taste, if I remember correctly, reminds you of these spices.
So, if you have "Kummer" or possibly weltschmerz, you have a couple of quick Kümmerlings and the world might look better (I doubt, esp. as it does not exactly help to reduce your waistline, v.s.)

Hans-Hermann