We analyzed the available evidence on whether protein sources with more leucine suppress appetite more than others, and what we’ve found so far is mixed. Sixty-eight studies or assertions suggest that protein sources higher in leucine may lead to greater appetite suppression, while sixty-two others do not support this idea [1]. Leucine is an amino acid found in proteins, and some researchers have proposed it might signal fullness to the brain. But our review shows this idea isn’t consistently backed. Some studies found that whey protein — which has more leucine than, say, soy or casein — was linked to reduced hunger after meals. Others found no difference in appetite between high-leucine and low-leucine proteins, even when the total protein amount was the same. The studies vary in design, population, and how hunger was measured, making it hard to draw a clear pattern. We also noticed that many of the supporting studies were small or short-term, and some didn’t control for other factors like calorie content, fiber, or fat in the meals. The refuting studies included both controlled trials and larger observational data, which adds to the uncertainty. So far, there’s no strong, consistent signal that leucine alone drives appetite suppression. It’s possible leucine plays a role, but it may be one of many factors — like how fast the protein digests, what else is in the meal, or individual differences in metabolism. What this means for you: If you’re trying to feel fuller longer, choosing high-protein foods is still a reasonable strategy. But focusing only on leucine-rich sources like whey or eggs isn’t clearly better than other protein options like beans, fish, or tofu — at least based on what we’ve reviewed so far.