Barley is not a complete protein. It contains all nine essential amino acids, but lysine is present in such low amounts that barley falls short of the threshold needed to qualify as “complete.” This makes barley similar to wheat, rice, and most other cereal grains, which share the same weakness. The good news: pairing barley with the right foods easily fills the gap.
What “Complete Protein” Actually Means
A complete protein provides all nine essential amino acids in sufficient quantities to meet your body’s needs. “Essential” means your body can’t manufacture them, so they must come from food. Having trace amounts of every amino acid isn’t enough. Each one needs to clear a minimum threshold relative to the total protein, and barley doesn’t do that for lysine.
Where Barley Falls Short
Lysine is barley’s first limiting amino acid, and threonine is the second. This pattern holds across nearly all cereal grains. The reason comes down to how barley stores its protein: roughly 30 to 40 percent of barley’s protein is a storage fraction called prolamin, which contains almost no lysine. Barley’s total protein ranges from about 7 to 14.6 percent by weight depending on variety, with lysine making up only 2.9 to 3.2 percent of that protein. For context, lysine in a complete protein source like quinoa or eggs is significantly higher.
Looking at the full amino acid profile per 100 grams of whole barley, the other essential amino acids are reasonably well represented: isoleucine at 522 mg, valine at 490 mg, phenylalanine at 522 mg, and tryptophan at 117 mg. But lysine sits at just 213 mg, dragging down barley’s overall protein quality score.
How Barley Scores on Protein Quality
Two standardized scores measure how well a food’s protein meets human needs. Barley earns a PDCAAS (Protein Digestibility Corrected Amino Acid Score) of 61 out of 100 and a DIAAS (Digestible Indispensable Amino Acid Score) of 55 out of 100. For comparison, rice scores 81 and 79 on the same two measures. A perfect complete protein like egg or milk would score close to 100. Barley’s low scores reflect both the lysine shortage and the fact that its protein isn’t fully digestible.
That digestibility issue partly comes from antinutritional compounds naturally present in barley: phytic acid, tannins, and enzyme inhibitors that reduce how much protein your gut can actually absorb. Simple preparation techniques like soaking, sprouting (germination), fermenting, or roasting break down many of these compounds and improve how much nutrition you get from the grain.
How Much Protein One Serving Provides
One cup of cooked pearled barley, the most common form sold in grocery stores, delivers about 3.5 grams of protein. That’s a modest amount, roughly comparable to a cup of cooked white rice. Hulled barley (where only the outermost husk is removed) retains more of the bran and germ, so it offers slightly more protein and fiber per serving. Either way, barley isn’t a food you’d rely on as a primary protein source. It works better as one component of a protein-rich meal.
How to Make Barley a Complete Protein
The classic solution is pairing grains with legumes. Grains like barley are low in lysine but rich in the sulfur-containing amino acids that legumes lack. Legumes are high in lysine but short on those same sulfur amino acids. Together, they cover each other’s gaps. A bowl of lentil and barley soup is a textbook example of a complete plant protein meal.
You don’t need to eat both foods in the same bite or even the same meal. Your body maintains a pool of amino acids throughout the day, so eating barley at lunch and beans at dinner still works. Practical pairings include:
- Lentils and barley in soups or stews
- Black beans served alongside a barley grain bowl
- Chickpeas mixed into a barley salad
- Split peas cooked with barley in a porridge
How Barley Compares to Quinoa and Buckwheat
If you specifically want a grain that’s already complete on its own, quinoa is the most popular option. Quinoa contains all essential amino acids in adequate proportions and packs 19 to 21 grams of protein per 100 grams of raw flour, compared to barley’s 10.8 to 11 grams. Buckwheat is another pseudocereal with a strong amino acid profile, scoring higher than quinoa on some protein quality indices.
That said, barley brings something quinoa and buckwheat don’t: exceptionally high levels of a soluble fiber called beta-glucan. In animal studies, barley’s beta-glucan has been shown to trigger the release of gut hormones that suppress appetite and improve insulin sensitivity, leading to reduced food intake and resistance to weight gain. These metabolic benefits are distinct from protein quality and represent a real nutritional advantage. If you’re building a varied plant-based diet, barley earns its place for fiber and gut health even though its protein is incomplete on its own.
Getting the Most From Barley’s Protein
If barley is a regular part of your diet, a few preparation steps can meaningfully improve how much protein and minerals your body absorbs. Soaking barley overnight before cooking reduces phytic acid, which otherwise binds to minerals and interferes with protein digestion. Sprouting the grain for one to two days goes further, breaking down multiple antinutritional compounds simultaneously. Fermentation, as in sourdough-style preparations, is the most effective single technique. Combining methods (for example, soaking followed by fermentation) produces the biggest improvements in nutrient availability.
None of this turns barley into a complete protein. The lysine gap is inherent to the grain itself. But maximizing digestibility means you get more value from the protein barley does provide, making it a stronger partner in meals where legumes or other lysine-rich foods round out the amino acid picture.