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Why Do Protein Shakes Cause Bloat and What’s Better, Soy or Whey?

Sometimes, when I write an article that has to do with what I eat, I show what I eat on Facebook (ok, most times). The article on The Men’s Health Abs Diet generated questions pertaining to which brand of protein powder I prefer and what about women? Well, what about women? 

“Women who take protein powders want to be sure that it’s going to be compatible with their hormones,” Shane Ellison author and chemist told me in an email. Mr. Ellison suggests avoiding proteins with estrogenic soy and sugar, “they throw estrogen balance out of whack due to increasing an enzyme known as aromatase,” he wrote. Additives, especially in protein powder, can do more than throw things out of whack.

Soy protein or whey protein was another common question asked on Facebook. I asked four experts this and other questions; each with diverse training and professions, but all within the health and fitness industry:

  • Robert Cleary -: a product developer and research scientist for Roche Pharmaceuticals, Consumer Health as well as Avon’s Women’s Health and Well Being.
  • Todd DeBloois and Dr. John Cuomo-: Todd DeBloois is a food scientist at USANA Health Sciences with more than 10 years of experience developing food products in the food industry. Dr. Cuomo is Executive Director of Research and Development at USANA Health Sciences and holds two patents for Olivol® along with over 20 other U.S. and international patents.
  • Chester Ku-Lea -: owner of AstroNutrition, a health and wellness supplement shop that stocks over 400 varieties of protein powder.

Soy vs. whey? Which is better?

“Soy contains isoflavones, which can have estrogen-like effects, so if you’re a bodybuilder, stick with whey. However, for those using soy as a protein source, it is recently thought to have a skin-smoothing effect on lines and wrinkles, so it depends on your objectives. Whey protein is considered nutritionally complete and has bioactive ingredients like immunoglobulins and lactoferrin that support the immune system. Whey is absorbed quickly so athletes like it for helping repair and rebuild muscles after a workout. Whey also has a fairly neutral taste and does not change the taste of foods you might add to it for example, fruit.” - Robert Cleary

“Whey protein has a higher density of many amino acids than soy, but soy has a better balance of essential amino acids. Both are good, complete proteins and choosing one would come down to preference and/or tolerance. I would recommend experimenting with different kinds of protein to determine your preference.” – Dr. John Cuomo

“Soy protein is an inexpensive high-protein powder supplement suitable for vegetarians or lactose intolerant. Soy does not contain an ideal balance of amino acids so it must be stacked with legumes, nuts or meat. The other issue with soy is that it contains phytoestrogens, estrogen-like properties that over time can have a cumulative estrogenic, toxic effect on both men and women. Soy should not be your main source of protein. Whey protein powder is the most common protein on the market. It contains all the essential amino acids and ranks the highest in biological value (measures the body’s absorption of protein) over eggs, red meat, and soy. As for the lactose intolerant – look for a micro-filtered protein powder that contains lactase enzyme to assist with your digestive issues. - Chester Ku-Lea

Is it possible to have protein powders that contain only whey?

“The product must say, whey-only or you cannot be sure. There are usually several names for individual ingredients and manufacturers often hide various proteins by simply announcing the one on the label their marketing department thinks will sell more of the product.” - Robert Cleary

“Absolutely. Some people have soy sensitivities or simply prefer whey protein, so we developed a chocolate whey shake that contains only whey protein.” –Todd DeBloois

They do exist but hard to find. The vast majority of protein supplements contain some type of flavoring, sweetener or enzyme. Buy unflavored whey if you want to cut down on additives. - Chester Ku-Lea

Why do some protein powders contain more additives than others?

It really depends on the claims the product manufacturer is making. There are artificial sweeteners, colors, preservatives, emulsifiers/stabilisers, anti-caking components, bulking ingredients, and glutamate (MSG) which work as flavor enhancers. Each one plays a specific role and is often added (or not) depending on the overall quality of the raw materials used, the formula, the taste, ‘mouth-feel,’ the manufacturing practices and equipment, and the price of producing the finished product and other considerations like, shelf-life. Bulking agents make it look like you’re getting more for your money. It can be difficult to separate the ‘marketing’ from the ‘science.’” - Robert Cleary

“Protein powders often contain many additives including flavors, colors, flow agents, masking agents and gums. These additives are added to protein powders to make them more palatable and appealing as well as making them easier to process, hydrate and package.” – Todd DeBloois

“A lot of protein powders these days have additives such as enzymes, fiber, BCAAs, creatine, or flavoring to their products. Some people love the idea of a pre-mixed protein with a dose of creatine while others want the most natural protein possible.” - Chester Ku-Lea

What additives should be avoided?

“The shorter the ingredient list the better! Whenever you see a long list of ingredients, you’re looking at more chemistry than nutrition. Remember, the further away the product is from it’s natural source in terms of processing, the further away from the natural energy the original food contained. Just because the manufactures sprinkle some vitamins in the formula doesn’t mean the body will recognize it as a food source.” - Robert Cleary

“I recommend looking for a shake that is ‘low-glycemic.’  Low GI shakes are designed to regulate your blood glucose levels to keep it at a pretty even keel.  Shakes that are not low GI contain a high amount of simple carbohydrates, which you should avoid.  They cause a rollercoaster ride in your blood glucose levels, starting off with a big spike and then dropping rapidly to even lower levels than baseline.  This then causes people to crave more simple carbohydrates.”  – Todd DeBloois

“Limit your use of sugars both natural (sucrose, fructose, maltodextrin) and unnatural (sucralose or aspartame). Look for proteins that contain healthy sweeteners such as stevia or xylitol.” - Chester Ku-Lea

Why do some powders have less grams of protein per serving than others?

“The number of grams a protein shake contains has to do with the intended end-consumer. For example, a bodybuilder or a person suffering from a digestive/absorption disorder may require higher amounts of protein. If it is a weight-loss protein shake, the objective is to support the muscles while losing fat so the protein is usually lower so as not to promote weight gain. You need to ask yourself “why am I increasing my protein, what is the benefit?” Then, choose one those claims match your intention.” - Robert Cleary

“There are actually a myriad of reasons why protein powders vary, but the main reason is probably the type of protein and the type of processing the protein has gone through. For example, there are protein isolates and protein concentrates.  Isolates have been processed and filtered to remove other components of the source material and yield a very high percentage (above 90%). Concentrates on the other hand are simply dehydrated and have lower yields (60-80%).” –Todd DeBloois

“Some powders contain less protein because they add ingredients such as creatine, vegetarian proteins, enzymes, amino acids, fiber or flavoring. Another reason would be the type of protein used. There is a difference between whey concentrate, whey isolate and hydrolyzed whey. 1. Concentrate is the cheapest, least effective whey protein that contains more lactose, fat and calories than isolate and hydrolyzed. 2. Isolate is the standard and contains a minimum 90% protein. 3. Hydrolyzed whey contains less protein but has been broken down and predigested for better absorption.” - Chester Ku-Lea

Why do some people experience bloat (gas) from protein shakes?

“Protein must be ‘broken down’ by the body into smaller parts or individual amino acids in order to be utilized. Because a protein shake will often contain more than the body can break down completely in the stomach and small intestine, the protein makes it to the large intestine in an undigested state. Once there, your intestinal fauna or bacteria are all too happy to eat up what’s left over. In doing so, they produce a variety of gases, such as methane, hydrogen and hydrogen sulfide (which stinks!). Hence, one can experience flatulence.” - Robert Cleary

“The bloating is generally attributed to the lactose found in protein shakes. I’d recommend either a vegetarian protein or a microfiltered protein that has lactase enzymes that increase absorption. It’ll definitely do the trick!” - Chester Ku-Lea

“The most likely culprit is soy protein. There are some polysaccharides in soy that humans cannot enzymatically break.  The microflora in the gut have the ability to break these polysaccharides down and metabolize them.  One of the by-products from this metabolism is gas.” – Dr. John Cuomo

Other Articles on Protein

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  • So glad you posted this! There are so many women who don’t understand what soy does and how it behaves in the body. Some of us need more estrogen, but many of us do not. Great article.

    Saranna DeWylde

    12:10 am

  • Thanks for posting the article, Stefan. Have you ever tried a protein that is non-whey, and non-soy? There are plenty on the market with varying effectiveness/taste etc. Personally, I prefer brown rice protein over anything else, mostly because of its health benefits.


    4:51 am

  • Top post for 2010: “Why do Protein Shakes Cause Bloat?”

  • Why Do Protein Shakes Cause Bloat and What’s Better, Soy or Whey? I ask the scientists at @USANAinc” via @stefanpinto

    Cece (@iamcece)

    12:18 pm

  • Wow. I had no idea. I already knew I cannot tolerate soy in dairy form. I have an intolerance to it (same symptoms as those who are lactose intolerant). Thank you for the information!


    1:00 am

  • Sadly, most soy is GMO. I try to avoid it all together, but the stuff is in almost EVERYTHING. :(


    4:40 pm

  • thanks Stefan! :-) "@stefanpinto: Why Do Protein Shakes Cause Bloat and What’s Better, Soy or Whey?: via @AddThis"

    Rey Tipz (@reytipz)

    2:34 am

  • Stefan, what protein do you drink?

    Michael H

    10:27 pm

  • Funny how much people rely on protein shakes for their diet goals. These are just supplements and not meant to be meal replacements.

    Amy Segel

    3:34 pm

  • When I first started working out, soy shakes were what I drank; I didn’t know the difference and they were more available at the grocery store than whey powder. Now, whey is widely available. It wasn’t until I started drinking whey that I saw the effects for building muscle.

    Stefan Pinto

    12:57 pm

  • I used to drink two soy shakes a day. Cut down to one. I’m not vegetarian, just thought they would be more healthy. I read about the estrogen effect soy has and that turned me off. I do agree that women don’t get enough protein. I think we are afraid of it and incorrectly assume it is for body builders only.

    Simone Cruz

    12:46 pm

  • I used to drink protein shakes as meal replacements. I did that for a month! Don’t recommend it. A lot of people think (and I was one of them) that protein shakes will help you to lose weight. I did lose weight but my energy levels went down. They are really just supplements. Thanks for the great info, Stefan!

    Jennifer (Jen) from Facebook ;-)

    2:27 pm

  • This is a very comprehensive article-and that’s a good thing! I know that soy is toxic to women who are breast cancer survivors because of the estrogen-like effect that soy has on them. The simply cannot consume soy because it stimulates the cancer cells to reproduce. The bottom line seems to be, consider all the information and make an informed decision.


    12:39 am

  • Why Do Protein Shakes Cause Bloat and What’s Better, Soy or Whey? « Fat to Fit by Stefan Pinto:

    Eric Peterson (@ericgpete)

    8:28 pm

  • Helpful article. I’m not much of a protein shake drinker mostly because of the bloat. I sometimes add a teaspoon of fennel seeds into the mixture when I do make a shake. Bananas will cause the most bloat from my experience.

    Carole Lori

    4:23 pm

  • Why Do Protein Shakes Cause Bloat and What’s Better, Soy or Whey?: via @AddThis

  • This is a great article Stefan. Very helpful and informative.

    Rona E

    2:15 am

  • Stefan, you didn’t tell us which protein powder you prefer.

    Adam Kastoria

    1:23 am

  • Why Do Protein Shakes Cause Bloat and What’s Better, Soy or Whey? by @StefanPinto

    @AnitaNelson (@ModelSupplies)

    7:11 pm

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