Protein Supplements: Casein and Soy

One of the myths about protein supplements is that they can magically help you build muscle…or lose weight. What many people don’t realize about protein powders and shakes is that unless you substitute them for other foods in the diet, you can very well end up gaining weight.


I recall that some of my patients would ask about using supplements or meal replacements (Glucerna, Boost, Ensure, etc.) to supplement their meal plan. They often didn’t understand that drinking those supplements on top of whatever they were eating for meals or snacks was contributing additional calories and carbohydrate. The same holds true for protein supplements. Always read the Nutrition Facts label to determine what’s in the product and decide how you’ll fit it into your eating plan.

Last week we looked at whey protein[1], a popular type of protein supplement. This week we’ll look at casein and soy supplements.

Casein Protein
What it is: Like whey, casein is a dairy product. Casein makes up roughly 80% of the protein in cow’s milk (the remaining 20% comes from whey). It’s also used as a binder in food, medicines, and even in nonedible products such as paint and nail polish.

Benefits: There’s probably no major benefit to choosing casein protein over whey protein. In terms of bodybuilding, both proteins can help build muscle. However, casein is a more slowly absorbed protein compared to whey (and you thought only carbs were quickly or slowly absorbed!). When casein is ingested, it forms a gel-like substance in the stomach, taking several hours to break down into amino acids. In contrast, whey protein breaks down in about 40 minutes.

Casein is also rich in glutamine, an amino acid needed to keep the immune system, the digestive system, and the brain in good working order. There is some evidence that casein may be helpful in lowering blood pressure[2]: In one study, subjects who consumed 3.8 grams of casein peptide daily for four weeks had an average drop in diastolic pressure (the bottom number) of 10.7 mm Hg and an average drop in systolic pressure (the top number) of 6.9 mm Hg.

Should you take it? If you’re interested in bodybuilding, whey protein may be your better bet for creating more muscle mass. However, casein protein is potentially helpful in preventing muscle loss. If you take casein for any reason, it’s recommended that you consume it before going to sleep. If you are using a meal replacement beverage for weight loss, experts recommend choosing one that contains both whey and casein to help better sustain you over several hours. Obviously, avoid casein altogether if you have a milk allergy. Keep in mind that casein is found in animal (cow, goat, sheep, and so forth) milk and products made with animal milk. Dairy alternatives such as soy, rice, and almond milk do not contain casein.

Soy Protein
What it is: Unlike whey and casein, soy protein is a vegetable (plant) protein. While most vegetable proteins are missing some amino acids, soy protein is considered to be a “complete” protein, meaning that it contains all nine essential amino acids. Soy protein isolate is the most pure form of soy protein and it is this form that is most often used in soy protein supplements.

Benefits: Soy protein is a complete protein without the saturated fat and cholesterol that’s found in animal protein sources. Soy also contains antioxidants[3] and other phytonutrients (plant-derived nutrients that may have health benefits) that may have positive effects on heart health[4], bone and calcium balance, menopausal symptoms, and recurrence of breast cancer. Bodybuilders may tend to choose whey protein for building muscle mass, but soy protein has been shown to preserve lean body mass, thanks to its antioxidant content. So, soy protein may have an advantage over whey protein because of the higher content of antioxidants. However, some evidence shows that whey protein has more of an appetite-suppressing effect than soy protein.

Should you take it? If you’re in the market for a protein supplement (powder or shake) for whatever reason, soy is a viable option. And if you’re a vegetarian, soy would be your choice. There’s still some controversy surrounding soy, though, in terms of breast cancer risk and diabetes control. Early studies showed that soy maybe was helpful in controlling blood glucose, but a newer study, published in The American Journal of Clinical Nutrition, showed that women with early, untreated Type 2 diabetes or prediabetes given a soy protein supplement had only a small improvement in blood glucose two hours after eating compared to a milk protein supplement and a milk and soy supplement. So, the jury is still out on the effects of soy on diabetes.

  1. Last week we looked at whey protein:
  2. blood pressure:
  3. antioxidants:
  4. heart health:

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Amy Campbell: Amy Campbell is the author of Staying Healthy with Diabetes: Nutrition and Meal Planning and a frequent contributor to Diabetes Self-Management and Diabetes & You. She has co-authored several books, including the The Joslin Guide to Diabetes and the American Diabetes Association’s 16 Myths of a “Diabetic Diet,” for which she received a Will Solimene Award of Excellence in Medical Communication and a National Health Information Award in 2000. Amy also developed menus for Fit Not Fat at Forty Plus and co-authored Eat Carbs, Lose Weight with fitness expert Denise Austin. Amy earned a bachelor’s degree in nutrition from Simmons College and a master’s degree in nutrition education from Boston University. In addition to being a Registered Dietitian, she is a Certified Diabetes Educator and a member of the American Dietetic Association, the American Diabetes Association, and the American Association of Diabetes Educators. Amy was formerly a Diabetes and Nutrition Educator at Joslin Diabetes Center, where she was responsible for the development, implementation, and evaluation of disease management programs, including clinical guideline and educational material development, and the development, testing, and implementation of disease management applications. She is currently the Director of Clinical Education Content Development and Training at Good Measures. Amy has developed and conducted training sessions for various disease and case management programs and is a frequent presenter at disease management events.

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