Plant-Based Protein Superfoods: A Complete Guide to Hemp Seeds, Quinoa, and Legumes

Hemp Seeds

Hemp seeds deliver approximately 31.6 g of protein per 100 g (raw, hulled), according to USDA FoodData Central (FDC ID: 170148). Three tablespoons (30 g), a practical daily serving, provide about 9.5 g of protein. Most of its protein is edestin, a storage globulin that made up about 70% of the protein in one hemp isolate and was highly digestible in a laboratory digestion model (Mamone et al., 2019). Hemp seeds also supply gamma-linolenic acid (GLA) and an omega-6 to omega-3 (linoleic to alpha-linolenic acid) ratio near 3:1 in the same USDA record.

All nine EAAs are present, including a methionine and cysteine content that is higher than most legumes. This makes hemp a useful complement to lentils or chickpeas, which are relatively low in sulfur-containing amino acids. A 2010 paper in the Journal of Agricultural and Food Chemistry measured PDCAAS values of 49–53% for whole hemp seed, 46–51% for hemp seed meal, and 63–66% for dehulled hemp seed, with lysine as the first limiting amino acid in every product (House et al., 2010, J Agric Food Chem). By that scoring, hemp is not a complete protein on its own, which is why pairing it with lysine-rich legumes works well.

Quinoa

Quinoa is a seed (technically a pseudocereal) that provides roughly 14.1 g of protein per 100 g uncooked (USDA FDC ID: 168874) and about 8 g per cup cooked (USDA FDC ID: 168917). It is one of the few grain-category foods with a complete EAA profile, notably high in lysine, the amino acid most commonly deficient in grain-heavy plant diets.

A 1992 study in Plant Foods for Human Nutrition found quinoa’s essential amino acid content higher than that of common cereals, with protein digestibility comparable to other high-quality food proteins (Ruales & Nair, 1992, Plant Foods Hum Nutr). Quinoa also contains notable amounts of iron, magnesium, and manganese, making it one of the more nutritionally dense grain alternatives for plant-based eaters.

Edamame

Edamame (immature soybeans) provides approximately 11.9 g of protein per 100 g cooked and roughly 18.5 g per 155 g cup shelled (USDA FDC ID: 168411). Soy is among the higher-scoring plant proteins, with a mean PDCAAS of about 0.92 across soy products in a 2022 review, though scores varied widely with processing (van den Berg et al., 2022).

Edamame is also a source of isoflavones (genistein, daidzein), which have been studied in the context of bone health and cardiovascular risk. The evidence on isoflavones is mixed. For soy protein itself, a 1995 meta-analysis of 38 controlled trials found that replacing animal protein with soy protein (an average of 47 g/day) lowered LDL cholesterol by about 12.9%, with larger drops in people with higher starting cholesterol (Anderson et al., 1995, NEJM). Later trials suggest smaller effects, and in 2017 the FDA proposed revoking its authorized health claim for soy protein and heart disease; that proposal has not been finalized (Federal Register, 2017).

Tempeh

Tempeh is fermented whole soybeans pressed into a dense cake. It provides about 20 g of protein per 100 g cooked (USDA FDC ID: 172467), more than regular tofu at about 8 g/100 g (USDA FDC ID: 172476), largely because tofu holds more water. The Rhizopus oligosporus mold used to make it produces phytases (Sutardi & Buckle, 1988), enzymes that partially break down phytic acid, an antinutrient that mainly reduces mineral absorption from legumes.

Published DIAAS data for tempeh itself are scarce, so whether fermentation lifts its score above that of unfermented soy is not established. The mold produces riboflavin, niacin, and vitamin B6 during fermentation but no active B12; bacteria that commonly ride along can make active B12, in amounts too variable to rely on (Keuth & Bisping, 1993).

Lentils

Lentils provide 17.9 g of protein per cup cooked (198 g) (USDA FDC ID: 172421). Cooked lentils scored a PDCAAS of 0.54 (split red) to 0.63 (whole green) in a rat assay, limited primarily by methionine and cysteine (Nosworthy et al., 2017). Combining lentils with a methionine-rich source (rice, hemp seeds, pumpkin seeds) raises the combined score. Lentils also deliver about 15.6 g of dietary fiber per cup.

Red lentils cook faster than green or black varieties and require no soaking. Dried lentils are also among the less expensive protein sources at retail.

Chickpeas

Chickpeas (garbanzo beans) supply about 14.5 g of protein per cup cooked (164 g) (USDA FDC ID: 173757). Cooked Kabuli chickpeas scored a PDCAAS of about 0.52 in the same rat assay, with tryptophan the first-limiting amino acid (Nosworthy et al., 2017). Like lentils, they are lysine-rich, so grain-based pairings complement them. Chickpeas are one of the more versatile legumes: they work in hummus, roasted as a snack, added to curries, or blended into flour for high-protein baking.

Chickpea flour (besan) retains most of the whole bean’s protein content, making it a useful ingredient in protein-dense plant-based cooking.

Black Beans

Black beans deliver about 15.2 g of protein per cup cooked (172 g) (USDA FDC ID: 173735). They contain resistant starch, which is not digested in the small intestine and functions as a prebiotic substrate in the colon. In a 2021 meta-analysis of 19 randomized trials, mostly using isolated resistant starch rather than whole beans, resistant starch modestly lowered fasting glucose and HOMA-IR (a measure of insulin resistance), though other insulin measures did not change significantly (Xiong et al., 2021).

Black beans also provide a meaningful iron contribution (about 3.6 mg/cup cooked, roughly 45% of the 8 mg RDA for men and 20% of the 18 mg RDA for premenopausal women), though this is non-heme iron with substantially lower bioavailability than heme iron. Vitamin C-rich foods eaten with a meal improve non-heme iron absorption, though a whole-diet study found the effect far smaller than single-meal tests suggest (Cook & Reddy, 2001).

Pumpkin Seeds

Pumpkin seeds (pepitas, hulled) provide approximately 30.2 g of protein per 100 g (USDA FDC ID: 170556), among the highest protein densities of any whole food. A 28 g serving (1 oz, about a quarter cup) supplies roughly 8.5 g of protein. They are also one of the best plant-based sources of zinc (2.2 mg per 28 g), a mineral that supports immune function and protein synthesis.

Pumpkin seeds are incomplete proteins, limiting in lysine (Sá et al., 2023), but pair well with lysine-rich lentils or chickpeas. They are also a source of magnesium (about 166 mg per 28 g, roughly 40% of the 420 mg RDA for adult men), which supports more than 300 enzyme reactions including those involved in protein metabolism.

Adding a handful of pumpkin seeds to a lentil-based grain bowl brings the meal’s combined protein closer to a complete profile while substantially increasing zinc intake. Zinc is a nutrient that tends to run lower in vegetarian diets, especially vegan ones (Foster et al., 2013).

Nutritional Yeast

Nutritional yeast is a deactivated yeast (Saccharomyces cerevisiae) typically sold as flakes or powder. It is protein-dense by dry weight and contains all nine EAAs, though serving sizes and protein per serving vary by brand, so check the label. It also supplies notable amounts of B vitamins.

Many commercial nutritional yeast products are fortified with vitamin B12, in amounts that vary considerably by brand. Fortified products make it one of the very few reliable B12 sources in a whole-food plant-based diet. That is a meaningful distinction, since B12 deficiency is a real and documented risk in fully vegan populations (Pawlak et al., 2014, Eur J Clin Nutr). Always check the label, because unfortified nutritional yeast does not provide meaningful B12.