Did you know that 100% whey protein can cause massive insulin spikes? Many don’t! In fact, those on ketogenic diets are told to avoid 100% whey protein drinks because they can throw you out of ketosis.

Research shows that while whey protein causes an increase in serum levels of leucine, isoleucine, and valine, it also causes an increase in the hormone glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1). The most interesting finding in this study is that not only did whey protein caused an increase in serum insulin levels, it caused an increase of insulin, GIP. GLP-1 greater than carbohydrates from white bread (1).

This study found that after ingestion of whey (grey bars), white bread (the carb group, white bars), and glucose alone (reference, black bar), whey protein caused the biggest spike in insulin (figure 1).

These findings of this study was backed by further research, thus confirming that simply supplementing 100% whey protein causes significant insulin spikes (2).

By incorporating a slower digesting protein with your whey, like casein protein, you will lower the overall insulin response. This is exactly what milk protein isolate is; a combination of whey and casein. Milk protein isolate is also the first ingredient in Select Protein.

Research shows that although casein and whey have the same rate of muscle protein synthesis overall, casein has a much lower insulin response (3-4). Once again, the whey+casein blends have taken the lead.

As you can tell, casein does not cause the same massive spike in insulin that whey does (refer to figure 1).


  1. Salehi, A., Gunnerud, U., Muhammed, S., et al. (2012). The insulinogenic effect of whey protein is partially mediated by a direct effect of amino acids and GIP on β-cells. Nutr Metab, 9:48.
  2. Claessens, M., Saris, W. H. M., & Baak, M. a van. (2008). Glucagon and insulin responses after ingestion of different amounts of intact and hydrolysed proteins. The British journal of nutrition, 100(1), 61-9.
  3. Reitelseder, S., Agergaard, J., Doessing, S., et al. (2011). Whey and casein labeled with L-[1-13C]leucine and muscle protein synthesis: effect of resistance exercise and protein ingestion. Am J Physiol Endocrinol Metab; 300(1): E231-42.
  4. Tipton, K. D., Elliott, T. A., Cree, M. G., Wolf, S. E., Sanford, A. P., & Wolfe, R. R. (2004). Ingestion of casein and whey proteins result in muscle anabolism after resistance exercise. Medicine and Science in Sports and Exercise, 36(12), 2073-2081.