Pea, Rice and Hemp Protein Powders: Amino Acid Profiles, Digestion and Heavy-Metal Questions

The question and the terms

This page profiles three plant proteins: what each contains, how well it is digested, what trials exist, and what testing questions apply. It does not rank them, and it does not answer whey versus plants; see Whey vs Plant Protein. Soy has its own page: Soy Protein. A "complete" protein contains all nine essential amino acids; see Protein Quality. Amino acids are the building blocks of protein, and lysine, methionine and leucine are essential ones.

Evidence labels used below: documented composition means measured in a laboratory; evidence in adequately nourished people means trials in healthy people; promising but limited means a few small or industry-linked trials; insufficient evidence means too little to judge.

Amino acid profiles and digestibility

In a laboratory analysis of commercial protein isolates, the share of lysine was 2.4 percent in the brown rice sample, 2.8 percent in hemp and 5.9 percent in pea, against 7.0 percent on average in animal proteins; methionine was 0.4 percent in pea, 2.0 in hemp and 2.5 in brown rice, against 2.5 percent in animal proteins. [5] Leucine was as low as 5.1 percent in hemp. [5] The samples were one each of rice and hemp and three of pea, so these figures describe those samples, not every product. [5]

A 2020 overview of digestibility-adjusted scores (DIAAS) classed pea, rice and hemp proteins in the lowest category, below 75, and reported that potato, soy and pea proteins could raise scores when mixed with other plant proteins. [6] Quality also varies within one source. A laboratory digestion study of three commercial pea ingredients found more methionine, the limiting amino acid in pea protein, was released from a less refined concentrate than from two isolates. [7] For hemp, a rodent and laboratory study found a hemp protein concentrate had significantly lower true protein digestibility than defatted hemp hearts, and a 2010 analysis found lysine was the first limiting amino acid in all hemp seed products tested. [8][9]

Side-by-side summary

What trials show

In the 12-week pea trial, overall group differences in biceps thickness were only a trend; in the weakest participants thickness rose more with pea than placebo and not differently from whey, and strength did not differ between groups. [10] In the 84-day trial in sedentary adults, changes in strength and muscle mass did not differ significantly between pea and whey; its authors state it was funded by an ingredient company. [11] In a trial of 24 resistance-trained men, 24-gram doses of rice or whey led to similar changes in body composition and performance over 8 weeks. [12] In a trial of 34 trained adults, 60 g a day of hemp product or soy product gave sex-specific differences in muscle thickness. [13] These are study amounts, not advice.

A blend of pea and rice protein did not raise blood essential amino acids above pea alone in ten healthy adults, while whey raised them more than pea or the blend. [14] That was a single-drink physiology study in young adults.

Digestion and allergy

Proper evidence not found, in the sources we searched, for trials of digestive comfort with pea, rice or hemp powders. We searched PubMed for pea and hemp protein digestibility and for pea allergy. A laboratory digestion study found known hemp allergens were eliminated by the isolate production process; it was not a clinical trial and does not show hemp is safe for allergic people. [15] Pea allergy was studied in 19 pea-sensitized children, 14 with doctor-diagnosed allergy; one pea protein was a major allergen in those children. [2]

Heavy-metal questions

A risk assessment using two published consumer-testing datasets (15 products in one, 133 in another) said plant-based protein powders tend to have a higher heavy-metal burden than animal-based ones, and concluded typical intake did not exceed its risk threshold. [3] The authors noted that validation details were not provided in either dataset. [3] An Irish laboratory study of 36 powders said metals were at acceptable levels but cautioned against excessive and prolonged use and advised following serving recommendations; its sample had only two pea powders, so it cannot rank plant sources. [16] Proper evidence not found for separate pea, rice and hemp heavy-metal data in the sources we read. We searched PubMed for protein powder heavy metals, plant powders and rice protein. See Protein Powder Safety and Quality Testing and Certifications.