I pass on any meal with too little of it.
But a meal with the right amount I heartily feast.
And a meal with too much I devour like a beast.
(scroll down for answer)
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The answer is: hunger.
Let's break down the riddle:
"An ingredient"It’s being referred to as an ingredient, not of the food, but of the experience of eating.
"I pass on any meal with too little of it."If you’re not hungry, you’ll likely skip the meal.
"But a meal with the right amount I heartily feast."When you’re appropriately hungry, food tastes great and you eat with enthusiasm.
"And a meal with too much I devour like a beast."When you're too hungry, you might eat ravenously or uncontrollably.