20 Foods High in Cysteine, Ranked by Serving Size

Cysteine is a sulfur-containing amino acid that your body uses to build proteins and, importantly, to make glutathione. A research review in the Journal of Nutrition explains that glutathione is built from glutamate, cysteine, and glycine, and that the availability of cysteine controls how much your cells can make. It is classed as semi-essential: your body can make it from methionine, so a diet short on cysteine is mainly a concern when methionine is low too.

The practical point is that a review of sulfur amino acid needs describes methionine and cysteine as a combined requirement, and says dietary cysteine can reduce how much methionine the body has to convert. Cysteine-rich foods are the same protein foods you would pick anyway, with meat, fish, soy, legumes, seeds, and eggs near the top. This guide ranks 20 of them by cysteine in a normal serving, and it pairs well with the guides to foods high in methionine and foods high in glutathione.

Best Food Sources of Cysteine, Ranked by Serving Size

Jump to: Soybeans | Chicken Breast | Beef Sirloin | Pork Loin | Turkey Breast | Lentils | Light Tuna | Shrimp | Tilapia | Cod | Hemp Seeds | Salmon | Chickpeas | Edamame | Tempeh | Eggs | Cottage Cheese | Wheat Germ | Sunflower Seeds | Rolled Oats | FAQ

All figures below come from The USDA FoodData Central database (SR Legacy), calculated for the serving size shown. One note on terms: the USDA reports this amino acid as cystine, the oxidized form made of two linked cysteine molecules, and does not list free cysteine separately. The numbers in this guide are therefore USDA cystine values, which is the standard way food tables show it. They are the best available way to compare foods, but they are not a measure of how much cysteine your body will absorb or use. Meal sizes for meat and fish are 3 oz cooked, about the size of a deck of cards.

1. Soybeans: The Top Plant Source

A cup of cooked soybeans supplies about 461 mg of cystine and 31.3 g of protein, the most of any food in this ranking per serving, according to the USDA.

Soybeans are one of the few plant foods that Harvard Health lists as a complete protein. A cup is a large portion, so the calorie count is higher than for lean meat.

Best eaten: added to soups, chili, and grain bowls, or mashed into a spread.

2. Chicken Breast: Lean and Easy to Portion

A 3 oz serving of roasted chicken breast provides about 337 mg of cystine with 26.4 g of protein for only 140 calories.

That makes it the best animal source here per calorie. Chicken is also versatile and easy to batch cook for the week.

Best eaten: sliced over salads, shredded into soups, or baked with vegetables.

3. Beef Sirloin: Red Meat With Dense Protein

Broiled top sirloin, trimmed of fat, gives you about 332 mg of cystine in a 3 oz portion, along with 25.7 g of protein.

Beef is also a source of iron, zinc, and vitamin B12. Choosing lean cuts keeps saturated fat and calories moderate.

Best eaten: as a stir-fry with vegetables or sliced thin over a grain bowl.

4. Pork Loin: A Lean Alternative to Beef

Roasted lean pork loin supplies roughly 310 mg of cystine per 3 oz, with 24.3 g of protein and 178 calories.

Trimmed pork loin is one of the leaner cuts of pork. It works well for meal prep because it slices cleanly and reheats without drying out too much.

Best eaten: roasted with root vegetables or sliced into sandwiches.

5. Turkey Breast: A Familiar Poultry Choice

Three ounces of roasted turkey breast provide about 266 mg of cystine and 24.4 g of protein.

The USDA entry used here includes skin, so removing it will lower the calories a little. Turkey is a simple swap for chicken in most recipes.

Best eaten: in wraps, soups, or as sliced deli-style roast from leftover dinners.

6. Lentils: Fiber and Cystine Together

One cup of boiled lentils has about 234 mg of cystine, 17.9 g of protein, and just 230 calories.

Lentils are among the best plant options here and also bring a lot of fiber, which helps with fullness. They cook in about 20 minutes with no soaking.

Best eaten: in soups, curries, or cold salads with vegetables.

7. Light Tuna: Canned and Convenient

Canned light tuna drained of its water gives you about 232 mg of cystine and 21.7 g of protein for only 99 calories.

It is one of the cheapest and quickest high-protein foods in the pantry. Light tuna is generally lower in mercury than albacore, but check current guidance if you eat fish often or are pregnant.

Best eaten: mixed with Greek yogurt, spooned over greens, or stuffed into a tomato.

8. Shrimp: Low Calorie, High Protein

A 3 oz serving of cooked shrimp supplies about 231 mg of cystine and 19.4 g of protein for around 101 calories.

Shrimp cooks in minutes, which makes it useful for weeknights. Some frozen shrimp are treated with additives to hold moisture, so read the label.

Best eaten: sauteed with garlic and vegetables or added to stir-fries.

9. Tilapia: A Mild White Fish

Cooked tilapia provides about 225 mg of cystine and 22.2 g of protein in a 3 oz fillet, with 109 calories.

Its mild taste suits people who do not usually like fish. It takes seasoning well and cooks quickly in a pan or oven.

Best eaten: baked with lemon and herbs or in fish tacos.

10. Cod: Very Lean Seafood

A 3 oz portion of cooked Atlantic cod offers about 208 mg of cystine, 19.4 g of protein, and only 89 calories.

Cod is one of the leanest proteins in this guide, so it suits calorie-controlled meals well.

Best eaten: baked, poached in broth, or pan-seared with a squeeze of lemon.

11. Hemp Seeds: The Best Seed on the List

Three tablespoons of hulled hemp seeds contain about 202 mg of cystine and 9.5 g of protein, the highest seed source in the USDA data used here.

Hemp seeds are small and easy to add without cooking. They are calorie dense, with 166 calories in this serving, so measure them if weight loss is your goal.

Best eaten: sprinkled on yogurt, oatmeal, or salads, or blended into smoothies.

12. Salmon: Protein With Omega-3 Fats

Cooked farmed Atlantic salmon supplies about 201 mg of cystine and 18.8 g of protein per 3 oz.

Salmon is higher in calories (175 here) because of its natural fat, which includes omega-3s. It is a good fit when you want fish to be the centerpiece of a meal.

Best eaten: baked or pan-seared with vegetables, or flaked into salads.

13. Chickpeas: A Pantry Staple

One cup of boiled chickpeas delivers about 195 mg of cystine and 14.5 g of protein.

Canned chickpeas work just as well after a rinse, which also lowers the sodium. They add bulk and fiber to meals without much prep.

Best eaten: roasted for snacking, blended into hummus, or tossed into salads.

14. Edamame: Soy You Can Snack On

A cup of prepared edamame gives you about 192 mg of cystine, 18.5 g of protein, and 188 calories.

Edamame are young green soybeans, so they come with the same soy protein in a lighter, snack-sized form. Keep a bag in the freezer for quick meals.

Best eaten: steamed with a pinch of salt or added to rice bowls and stir-fries.

15. Tempeh: Fermented Soy

A 3 oz serving of tempeh has about 164 mg of cystine and 17.2 g of protein for 163 calories.

Tempeh is made from fermented soybeans pressed into a firm cake. It has a nutty taste and holds its shape when cooked.

Best eaten: sliced and pan-fried, crumbled into chili, or marinated and baked.

16. Eggs: The Everyday Breakfast Option

One large hard-boiled egg provides about 146 mg of cystine, 6.3 g of protein, and only 78 calories.

Two eggs would roughly double those figures. Eggs are inexpensive and fit into almost any meal of the day.

Best eaten: hard-boiled for snacks, scrambled with vegetables, or sliced onto toast.

17. Cottage Cheese: The Best Dairy Pick

A cup of 2% cottage cheese supplies about 140 mg of cystine and 23.6 g of protein. Per 100 g, dairy is lower in cystine than meat or soy, so you need a full cup to land on this list.

It makes the list because the serving is large and very high in protein. Sodium varies by brand, so compare labels.

Best eaten: topped with fruit or tomatoes, or blended into pancakes and dips.

18. Wheat Germ: A Small Spoonful of Cystine

One ounce of wheat germ provides about 130 mg of cystine and 6.6 g of protein.

Wheat germ is the nutrient-rich core of the wheat kernel and is sold toasted. It contains gluten, so it is not suitable for people who avoid it.

Best eaten: stirred into yogurt, oatmeal, or baked goods.

19. Sunflower Seeds: A Handy Snack

An ounce of dried sunflower kernels gives you about 128 mg of cystine and 5.9 g of protein.

A small handful goes a long way, but the calories add up quickly at 166 per ounce, so measure your portion.

Best eaten: on salads, in trail mix, or blended into homemade seed butter.

20. Rolled Oats: The Whole Grain Option

A typical dry serving of rolled oats, about a third of a cup, provides roughly 123 mg of cystine and 3.6 g of protein.

Oats are a whole grain that lands on this list mainly because a bowl of oatmeal is such a common breakfast. Double the serving and you double the numbers.

Best eaten: as oatmeal made with milk, overnight oats, or in baked oat cups.

Quick Reference: All 20 Cysteine Foods at a Glance

5 Practical Tips for Getting Cysteine From Food

• Eat enough total protein. Cysteine comes packaged with protein, so a diet that meets your protein needs usually supplies it. Harvard Health notes the 0.8 g per kg RDA is a minimum, not an ideal. The guide to high-protein foods has more options.
• Mix animal and plant sources. Chicken, fish, and eggs sit alongside soybeans, lentils, and seeds in this ranking, so any eating pattern can get there. Vegetarians can lean on soy, lentils, chickpeas, hemp seeds, and eggs.
• Pair cysteine with the other glutathione building blocks. Glutathione needs glycine and glutamate as well. See the guides to foods high in glycine and foods high in glutamine.
• Do not forget methionine. Your body makes cysteine from methionine, and most of the foods on this list supply both. The foods high in BCAAs guide covers other amino acids found in the same proteins.
• Watch portion size for dense foods. Hemp seeds, sunflower seeds, and salmon carry more calories per mg of cystine than cod, shrimp, or tuna, so measure them if weight loss is the goal.

Frequently Asked Questions About Cysteine

Is cysteine an essential amino acid?

No, it is classed as semi-essential. Your body can make cysteine from methionine, which is essential. Because the two are needed together, researchers often discuss them as a combined sulfur amino acid requirement.

What is the difference between cysteine and cystine?

Cystine is two cysteine molecules joined by a sulfur bond. Food databases such as the USDA report cystine, and the body can convert between the two forms.

What foods are highest in cysteine?

Per serving in this guide, cooked soybeans lead, followed by chicken breast, beef sirloin, pork loin, and turkey breast. Among seeds, hemp seeds are highest.

Do vegetarians and vegans get enough cysteine?

Generally yes when they eat enough total protein. Soybeans, lentils, chickpeas, edamame, tempeh, and hemp seeds all appear in the top 15 of this ranking.

What does cysteine do in the body?

It is used to build proteins and to make glutathione, which the Journal of Nutrition review cited above describes as a key antioxidant and cellular protector. Cysteine is also supplied as a supplement called N-acetylcysteine, but supplements are a medical question, not a food question, so talk to your doctor before using one.

The Bottom Line

Soybeans, chicken, beef, pork, turkey, lentils, and fish lead the list for cysteine per serving, while hemp seeds, eggs, cottage cheese, and oats show that plant foods and dairy contribute too. You do not need to track cysteine on its own. Build meals around good protein sources, mix them across the week, and use the table above to swap foods that fit your diet.

Nutrient values in this article are from the USDA FoodData Central database (SR Legacy), reported as cystine, and calculated for the serving sizes listed. Actual values vary by brand, cut, and preparation.

This article is for educational purposes and is not a substitute for advice from a registered dietitian or physician. Talk to a healthcare professional before changing your diet or taking supplements, especially if you have kidney disease, liver disease, or another medical condition.

Save It For Later