Written by the Spacemilk team · Last updated October 2026

No single ingredient makes a protein powder bad, but a few are worth checking for: sugar alcohols, inulin or chicory root, some gums, lactose, added sugars, caffeine, and allergens you need to avoid. Also look for a full ingredient list with no proprietary blends, and proof of independent testing. How much any of these matters depends on your body and your goals. If you have IBS or another digestive condition, a doctor or registered dietitian can help you work out your own triggers.

How do you read a protein powder label?

Start with the ingredient list, not the front of the tub. On a food label, ingredients are listed in descending order of predominance by weight, so the first few make up most of what you're eating (21 CFR 101.4). Then check three things on the panel:

• Serving size. How many scoops make one serving, and how much protein that serving gives you.
• Added Sugars. The Nutrition Facts label lists added sugars on their own line, with a Daily Value of 50g (FDA).
• Allergen statement. Look for the "Contains" line or allergen names in parentheses after an ingredient.

Which protein powder ingredients are worth checking for?

None of these is a problem for everyone. Each has a specific reason some people skip it.

Ingredient	Why some people avoid it	Names on the label
Sugar alcohols	Can cause gas, bloating and a laxative effect, more so at higher doses	Sorbitol, mannitol, xylitol, maltitol, isomalt, erythritol
Inulin and chicory root	Fermentable fiber (a fructan, one type of FODMAP)	Inulin, chicory root, oligofructose, FOS, "prebiotic"
Some gums	Fermented by gut bacteria; some people notice discomfort	Xanthan gum, guar gum
Lactose	A common trigger for bloating and gas	Whey concentrate, milk protein, milk solids
Added sugars	Adds calories you may not expect in a protein shake	Sugar, dextrose, syrups, honey, fruit juice concentrate
Caffeine and stimulants	Can affect sleep, heart rate and nerves	Caffeine, coffee, green tea, "energy" or "pre-workout" blends
Major allergens	Can cause allergic reactions	Milk, eggs, soy, wheat, peanuts, tree nuts, fish, shellfish, sesame

Sugar alcohols

Sugar alcohols, also called polyols, sweeten without sugar. They aren't fully absorbed, so some reach the large intestine. A systematic review found polyols can cause dose-dependent flatulence, bloating, abdominal discomfort and laxative effects in healthy people and in people with IBS, and that people with IBS tend to notice symptoms at lower doses (Lenhart and Chey, 2017). Erythritol is the exception in that review: about 90% is absorbed in the small intestine. Monash University still lists it among the polyols to watch for on labels (Monash University).

Inulin and chicory root

These are added as fiber and are often marketed as "prebiotic." Monash lists inulin, FOS and chicory root as fructans, a group of FODMAPs (Monash University), and advises people with IBS to avoid protein powders labeled "prebiotic" (Monash University). In a controlled trial in healthy adults, inulin fibers mildly increased digestive symptoms, mostly flatulence and then bloating. A 10g dose of oligofructose, the shorter-chain form, increased symptoms substantially compared with control (Bonnema et al., 2010).

Gums

Gums thicken a shake. Xanthan gum isn't absorbed intact and is expected to be fermented by gut bacteria. Europe's food safety agency found no safety concern at normal use, and noted that some adults taking large daily doses for ten days reported abdominal discomfort (EFSA, 2017). A scoop holds far less.

Lactose

About 36% of people in the United States have lactose malabsorption, with symptoms like bloating, diarrhea and gas (NIH/NIDDK). Whey concentrate carries more lactose than whey isolate, which is processed further (Monash University).

Added sugars

Added sugars include sugar, dextrose, syrups, honey and concentrated fruit juice. Sugars that occur naturally in milk or fruit aren't counted (FDA). The Added Sugars line tells you how much a serving contributes toward the 50g Daily Value.

Caffeine and stimulants

Some protein blends add coffee, caffeine or "energy" ingredients. The FDA cites 400mg a day as an amount not generally associated with negative effects in healthy adults, but sensitivity varies widely. Too much can cause jitters, a racing heart, trouble sleeping and an upset stomach. If you're pregnant, breastfeeding, or take medications that interact with caffeine, ask your doctor (FDA).

Allergens

US law names nine major food allergens: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans and sesame. Labels must declare them. "May contain" statements about cross-contact aren't required by law (FDA). Our guide to allergen-free protein powder goes deeper.

What is a proprietary blend, and what is amino spiking?

A proprietary blend is a group of ingredients listed under one name. For dietary supplements, the label gives the blend's total weight and lists its ingredients from most to least, without each one's amount (21 CFR 101.36). So you can't tell how much of each you're getting.

Amino spiking is a related concern about the protein number itself. The standard lab methods for protein, Kjeldahl and Dumas, measure nitrogen, then convert it to protein. Anything rich in nitrogen can inflate the result (Moore et al., 2010). Researchers describe "spiking" powders with free amino acids to raise the measured protein content (Faller et al., 2019). A shorter ingredient list with no blends, and independent testing, make this easier to rule out.

Why does third-party testing matter?

Independent testing is a check on what's actually in the tub. According to the NIH Office of Dietary Supplements, products that pass testing by an independent organization were properly manufactured, contain the ingredients on the label, and don't have harmful levels of contaminants. Testing doesn't guarantee a product is safe or effective.

Contaminants are a real consideration for any food grown from the earth. Metals such as lead, arsenic, cadmium and mercury occur naturally in the environment and can be present in foods because they're in the soil, water or air where foods are grown, raised or processed (FDA). That's why testing every batch, and publishing the results, matters.

What should you look for in a protein powder?

• A complete protein. All nine essential amino acids. Our guide to PDCAAS explains how protein quality is scored.
• A short, fully disclosed ingredient list. Every ingredient named, no proprietary blends.
• Low or no added sugar. Check the Added Sugars line.
• Known triggers left out. If you're sensitive, look for no sugar alcohols, no added inulin or chicory root, and little or no gum. More in our guide to protein powder for a sensitive stomach.
• Allergens that fit your needs. Check the "Contains" line.
• Caffeine only if you want it.
• Batch testing you can check. Results published for each lot, ideally matched to the lot code on your bag.

How does Spacemilk's label line up?

Spacemilk is the first protein made from baker's yeast, and we built it around this list.

• Protein: 20g complete protein per serving, with a protein quality score of PDCAAS 1.0.
• Sugar: 0g sugar. The flavored versions are sweetened with Reb M, a fermented rice sweetener, and most also use thaumatin. Neither is a sugar alcohol.
• Left out: no dairy or lactose, no sugar alcohols, no gums, no added inulin or chicory root, and no artificial flavors, sweeteners, colors or preservatives. It's formulated to be low in FODMAPs.
• Fiber: the flavored versions contain a small amount of konjac fiber for texture. It's a fiber, not a gum.
• Ingredients: Unflavored is one ingredient, yeast protein isolate. Every ingredient is named on the bag, with no proprietary blends.
• Allergens: free from all 9 major allergens.
• Testing: every batch is independently third-party tested for heavy metals, microbials, pesticides and allergens (gluten, dairy, soy and peanuts), and every result is published. Match the lot code on your bag on our testing page.

Learn more about Spacemilk Complete Protein.

Is ingredient sensitivity the same for everyone?

No. An ingredient one person never notices can bother someone else, and dose matters: two scoops doubles every ingredient. If a powder bothers you, change one thing at a time and give it a few days.

Talk to your doctor or a registered dietitian if you have IBS, inflammatory bowel disease, celiac disease or another digestive condition, a food allergy, kidney disease, or you're pregnant or nursing. Monash advises following a low-FODMAP diet with a dietitian or healthcare professional (Monash University). Persistent or worsening symptoms deserve a medical check, whatever powder you use.

FAQ

What is the worst ingredient in protein powder?

There isn't one for everyone. The ingredients most worth checking are sugar alcohols, inulin or chicory root, gums, lactose, added sugars, caffeine and your own allergens. Which one matters depends on you.

Which protein powder doesn't cause bloating?

No powder can promise that for everyone. Your best odds are one with no lactose, no sugar alcohols, no added inulin and few or no gums, tried at a small serving first.

What does "clean protein powder" mean?

It has no formal meaning. In practice, people use it for a short, fully disclosed ingredient list, low added sugar and independent testing. Check the label and the test results rather than the word.

How do I know if a protein powder is third-party tested?

Look for published results from an independent lab, ideally for each batch, that you can match to the lot code on your container.

Sources

• Lenhart A, Chey WD. A systematic review of the effects of polyols on gastrointestinal health and irritable bowel syndrome. Advances in Nutrition, 2017. doi:10.3945/an.117.015560
• Bonnema AL, et al. Gastrointestinal tolerance of chicory inulin products. Journal of the American Dietetic Association, 2010. doi:10.1016/j.jada.2010.03.025
• EFSA Panel on Food Additives. Re-evaluation of xanthan gum (E 415) as a food additive. EFSA Journal, 2017. doi:10.2903/j.efsa.2017.4909
• Moore JC, et al. Total protein methods and their potential utility to reduce the risk of food protein adulteration. Comprehensive Reviews in Food Science and Food Safety, 2010. doi:10.1111/j.1541-4337.2010.00114.x
• Faller AC, et al. Investigating appropriate molecular and chemical methods for ingredient identity testing of plant-based protein powder dietary supplements. Scientific Reports, 2019. doi:10.1038/s41598-019-48467-9
• Monash University: Food processing and FODMAPs; Protein powders and IBS; About FODMAPs and IBS
• NIH/NIDDK: Definition and facts for lactose intolerance
• NIH Office of Dietary Supplements: Dietary supplements: what you need to know
• FDA: Added sugars on the Nutrition Facts label; Spilling the beans: how much caffeine is too much?; Food allergies; Environmental contaminants in food
• US Code of Federal Regulations: 21 CFR 101.4 (ingredient order); 21 CFR 101.36 (proprietary blends)