Why was this study done?

Determining the best macronutrient (protein, carbohydrate, fat) makeup of a meal is difficult. This study was designed to investigate the effects of 58 grams of carbohydrate along with varying amounts of protein 0, 15.8, 24.1, 33.6, and 49.9 grams to determine the effects of serum glucose and insulin.  

What did the study find?

The protein content of the meal was the best determinant of how far blood glucose would spike following ingestion.

Spiller GA, et al. Effect on Protein Quantity and Quality on the Serum Glucose Response to the Sugars of a Formula Diet. Am J Clin Nutr, 1985. 41(4): p. 854.PDF Abstract: Am J Clin Nutr, 1985.