A dietician is studying the data collected in an experiment performed by a colleague. The experiment was designed to test the hypothesis that abnormally high blood urea nitrogen (BUN) levels are directly related to increased protein. Nitrogen in the blood in the form of urea, called blood urea nitrogen (BUN), is a toxic by-product of the breakdown of proteins and is filtered out of the blood by the kidneys. The results of the colleague's investigation are given below. 30-day Protein Intake vs. Blood Urea Nitrogen Levels Test Subject Grams of protein consumed per day (grams) Blood urea nitrogen level (mg/dL) 1 50 6 2 70 15 3 100 50 4 150 30 5 200 40 Currently Recommended Protein Intake 105 g/day* Normal Blood Urea Nitrogen (BUN) 6–20 mg/dL** Moderate to Severe Kidney Failure BUN Level greater than 60mg/dL * Value suggested is for a healthy 154 pound man who regularly exercises. ** mg/dL means milligrams of BUN per deciliter of blood Which of the following best describes the dietician's criticism of this experiment, and how does she recommend improving it? The test subjects may have also consumed carbohydrates and fats during the 30-day trial, so the amount of carbohydrates and fats in the test subjects' diets should be limited. Since BUN is filtered by the kidneys, reduced kidney function could also explain the BUN levels in the test subjects. Therefore, the kidney health should be measured and only test subjects with fully functioning kidneys should be used. Since the recommended daily protein intake is 105 g/day for a 154-pound man, the test subjects should all be men of the same weight, and they should all consume about 105 g/day of protein during the 30-day trial. Since abnormally high BUN levels result from increased protein intake, and high BUN levels can be a sign of kidney failure, the test subjects' protein intake should be limited to 105 g/day and below.