Seitan is low in one essential amino acid, lysine, and pairing it with a lysine-rich food turns it into a complete protein. The simplest combinations are legumes (beans, lentils, chickpeas), soy products (soy sauce, tofu, edamame), or nutritional yeast, either cooked into the seitan dough or eaten alongside it in the same meal.
Why Seitan Isn’t Complete on Its Own
Seitan is made from vital wheat gluten, which is roughly 75% protein by weight. Two ounces of seitan delivers about 17 grams of protein, roughly matching the same amount of chicken breast. The problem isn’t quantity. It’s quality.
Wheat gluten contains just 1.42 grams of lysine per 100 grams of protein. That’s well below the threshold your body needs. Adults require about 30 mg of lysine per kilogram of body weight per day, so a 70 kg (154 lb) person needs around 2,100 mg daily. If seitan is your primary protein source and you’re not supplementing with lysine-rich foods, you’ll consistently fall short. This single deficiency drags down the overall usefulness of all that protein, because your body can only build new tissue at the rate its most limited amino acid allows.
This shows up clearly in protein quality scores. Wheat scores a 0.54 on the PDCAAS scale (a standardized measure of protein quality), compared to 0.92–1.00 for soy protein isolate and a perfect 1.00 for most animal proteins. That 0.54 essentially means your body can only use about half the protein in wheat gluten as efficiently as it could use an equal amount of egg or dairy protein. Fixing the lysine gap closes most of that difference.
Best Foods to Pair With Seitan
Any lysine-rich food will do the job. The most practical options fall into three categories.
- Legumes: Chickpeas, black beans, lentils, and peanuts are all high in lysine while being low in the sulfur-containing amino acids that wheat gluten has plenty of. This makes them a textbook complementary pairing. A side of lentils, a chickpea salad, or even peanut butter in the same meal balances seitan’s profile.
- Soy products: Soy is one of the few plant proteins that’s already complete on its own, with a PDCAAS near 1.00. Cooking seitan in soy sauce adds some lysine, but for a meaningful boost, incorporate tofu, tempeh, edamame, or soy milk into the meal.
- Nutritional yeast: This is a particularly effective option because it’s easy to mix directly into seitan dough. Nutritional yeast contains about 65 mg of lysine per gram of protein, which is more than four times the concentration found in wheat gluten. Yeast protein contains all essential amino acids in quantities that meet international nutrition recommendations, making it a complete protein on its own. Two to three tablespoons kneaded into your dough meaningfully shifts the amino acid balance.
Cook It In or Eat It Alongside
You don’t have to eat complementary proteins in the exact same bite. Eating them in the same meal, or even spread across the same day, gives your body the full set of amino acids it needs. That said, building complementary ingredients directly into your seitan recipe is the most reliable approach because it improves every serving automatically.
Common techniques for building lysine into the dough itself:
- Nutritional yeast in the dough: Add 2–3 tablespoons per cup of vital wheat gluten. It dissolves easily and adds a savory, umami flavor that most people enjoy.
- Chickpea flour blended in: Replace 10–20% of the vital wheat gluten with chickpea flour. This lowers the total protein density slightly but improves the amino acid balance. It also changes the texture, making the seitan a bit softer and less chewy.
- Soy sauce or tamari in the liquid: Using soy sauce as part of your mixing liquid adds lysine in smaller amounts while deepening the flavor. This alone won’t fully close the gap, but it contributes.
- Tofu blended into the dough: Pureeing silken tofu into the wet ingredients before mixing with gluten is a popular technique. It softens the final texture and adds a meaningful dose of complete soy protein.
How Much Complementary Protein You Need
You don’t need equal parts seitan and beans. Because lysine is the only significantly limiting amino acid, even a moderate serving of a lysine-rich food covers the gap. A rough guideline: for every 100 grams of seitan you eat, a half-cup of cooked lentils or beans, a couple tablespoons of nutritional yeast, or a quarter block of firm tofu provides enough lysine to bring the meal’s protein quality close to that of animal protein.
The other essential amino acids in wheat gluten, including leucine, isoleucine, valine, and the sulfur-containing amino acids, all meet or come close to recommended levels. Threonine is slightly on the lower side at 2.54 g per 100 g of protein, but legumes and nutritional yeast cover that as well. Nutritional yeast, for instance, contains 48 mg of threonine per gram of protein, nearly double the concentration in wheat gluten.
Digestibility Matters Too
Protein quality isn’t just about amino acids. Your body also has to break down and absorb the protein efficiently. Wheat gluten has a true digestibility of about 90%, which is comparable to most other plant proteins and not far below animal sources. The real issue is what happens after digestion: studies measuring how much wheat protein the body actually retains and uses for building tissue found a retention rate of about 66%. The rest gets broken down for energy or excreted.
That 66% retention rate is lower than what you’d see with animal protein or soy, and it’s partly driven by the lysine limitation. When you correct the amino acid imbalance by pairing seitan with complementary foods, your body can use more of that absorbed protein for its intended purpose: repairing muscle, producing enzymes, and maintaining tissues. In practical terms, this means a bowl of seitan stir-fry with edamame does meaningfully more for your muscles than the same amount of seitan eaten alone.
A Simple Rule of Thumb
If you eat seitan regularly, make legumes, soy, or nutritional yeast a consistent part of those meals. The easiest single change is adding nutritional yeast to your dough recipe, since it integrates seamlessly and provides the highest concentration of the exact amino acid seitan lacks. Beyond that, any bean, lentil, or soy product on the same plate finishes the job. You don’t need to measure milligrams or calculate ratios. Just pair seitan with one of these foods at most meals, and the protein you’re getting becomes functionally complete.