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Cooked yellowfin tuna leads clearly at about 29 g of protein per 100 g. Most of the other fish here fall between roughly 20 and 24 g, so calories, omega-3 fat and, for certain species and groups, mercury often matter more than a one-gram protein difference.
Parmesan dominates per 100 grams because it is so concentrated, but most people do not eat it in the same portion as a fresh cheese. Once serving size enters the picture, the ranking tells a different story.
The ranking changes when the question shifts from 'how much protein is in 100 grams?' to 'how much protein do I get for 100 calories?' Lean fish, egg whites, turkey and chicken suddenly move toward the top.
Soybeans and lupini beans clearly separate themselves when cooked legumes are compared fairly. Lentils, chickpeas and common beans, on the other hand, are close enough that chasing tenths of a gram is not very useful.
Chicken and turkey breast are the leanest examples, but pork tenderloin can be close. Lean beef supplies more heme iron, and cut choice often matters more than the animal name.
Chia and flax lead on fiber per 100 grams, while a full serving of beans or lentils can contribute more total fiber than a spoonful of seeds.
Animal proteins generally have high digestibility and favorable essential-amino-acid profiles. Plant foods can fully meet protein needs with adequate variety and also provide fiber that meat, fish, eggs and dairy lack.
Tempeh, tofu, seitan, soybeans and legumes are easy to use as the protein center of a plant-based meal. Nuts and seeds add protein, but their usual servings are smaller.
Aged cheeses, seeds and lean cooked meats rank among the most protein-dense foods per 100 grams, but serving size and water content can change which foods contribute the most protein to an actual meal.