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, 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: 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 and other phytonutrients (plant-derived nutrients that may have health benefits) that may have positive effects on heart health, 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.

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  • Tammy

    Thank you for this great information. Easy to read and understand. I have recently been diagnosed Hyperglycemic and am a bit overweight. I have been told I need to eat more, especially breakfast. I don’t typically eat breakfast and if I do, it’s a berry smoothie, which is made from all fruit, green tea, cinnamon and psyllium husks. No protein there.
    Looking for a good source of protein that will be easy to eat in the morning and since I already make a smoothie, why not just add some protein powder to it. Can’t get much easier than that.

    you helped me understand the difference between proteins and given me good information to go to my MD with, at my next visit.

  • Dr Jawad

    My father is a type 2 Diabetic and he is also on one kidney. His blood sugar level are normal and his renal function tests are normal as well. I am concerned about his muscle bulk which he is losing and his arms and legs are very thin. Please can you recommend a supplement that would increase his muscle mass/bulk?

    Kind Regards,

    Dr Amjad

  • acampbell

    Hi Dr. Amjad,

    The loss of lean muscle mass due to aging is called sarcopenia, and it’s unfortunately very common in older adults. One of the best things that your father can do to increase his muscle mass and prevent further loss of muscle is to do resistance exercises, such as using hand weights, resistance bands, or weight machines at the gym. A trainer or physical therapist can show you and your father how to do these. It’s also important that your father consumes an adequate amount of calories and protein. It might be helpful to meet with a dietitian to review his food intake. Finally, there is a supplement called Juven, made by Abbott Laboratories, that has been shown in studies to help increase muscle mass in older adults. You might look into this and speak with his doctor about it, as well.