How to Find Which Items Give You a Specific Status Effect
Searching by Effect
Open JEI and click any status effect icon on the item overlay, or click an active effect in your inventory's effect box, to enter the Effects category. Type the effect's name into the JEI search bar to narrow the list, then click the effect you want. The detail page lists the items that can grant that effect.
What the Item List Covers
Just Enough Effect Descriptions automatically detects food items as effect providers, so most of what you'll see are foods, drinks, and similar consumables. Potions and other sources may also appear depending on how the effect is registered. If an item you expect is missing, it likely means the mod that adds it hasn't declared the effect-providing relationship, so the plugin can't detect it automatically.
Using This While Playing
This is the fastest way to answer questions like "what do I eat to get this buff" or "which mod's item gives this debuff." Hover each listed item to read its tooltip, and check the effect's color swatch so you can recognize the particle color in-world. If you're a pack author or modder, remember that adding the correct description and provider entries to a language file or config is what makes these lists complete — players only see what's been registered.