How to Calculate Calories in Human Blood

Is donating blood a path to weight loss? The standard U.S. blood donation weighs more than a pound. Dietitians tell us that losing 1 lb. is equivalent to losing 3,500 calories. Does this mean that after donating blood we are down more than 3,500 calories, and therefore can indulge in all sorts of calorie-rich foods just to gain that pound back? Or conversely, that donating blood is a good way to start a diet? The answer to all these questions is "No," and these steps will help you understand why not.

Things You'll Need

• Electronic calculator
• Paper
• Pen or pencil

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Instructions

• 1

  Identify the liquid and cell components of blood. Lab tests of blood include a value called "hematocrit." This value is the percentage of blood that is cells, versus the percent that is liquid, and is determined by spinning a tube of blood in a centrifuge to pack the cells to one end. Whatever percentage that is not packed cells is plasma. On average, adult men's blood has a lower plasma content than women's blood, because men have more red blood cells. Use either the average male value of 55 percent plasma or the female value of 60 percent plasma, or use your own from lab test results.

• 2

  Calculate calories for protein in plasma. Volumes need to be converted to grams, because calorie content is calculated with grams. Assume a standard blood donation of 500 ml. Blood is denser than water by 6 percent, so multiply 500 ml by 1.06 to get to grams. Multiply that by the percentage of plasma and divide by 100 to get to grams of plasma. Multiply that by .07, because plasma, according to John Kimball's online biology textbook is on average 7 percent protein and the rest mostly water, to get grams of protein. Finally, multiply that by four to get protein calories.

• 3

  Calculate calories for sugar and fat in plasma. For people who do not have diabetes, fasting blood sugar is around 0.09 gm per 100 ml of plasma, more familiarly expressed as 90 mg/dl. Multiply the amount in grams by 2.75 for men or 3.00 for women, i.e., equal to how many hundreds of milliliters of plasma there are in 500 ml of blood, and then multiply by four to get to calories. For calories from fat, use 0.5 g per 100 ml of plasma, multiply hundreds of mls of plasma, by 9--for calories from grams of fat--to get to calories. The 0.5 g/dl covers triglycerides and fatty acids in lipoproteins, but not cholesterol, as cholesterol is not metabolized for energy.

• 4

  Calculate calories from red blood cells. RBCs are mostly water and protein, the protein almost entirely hemoglobin, with negligible contributions from fat or carbohydrates. Hemoglobin does not conform to the rule of 4 calories per gram because the heme portion of the molecule is not metabolized for energy. Using average hemoglobin values of either 160 g/L for men or 140 g/L for women, multiply by 0.5 to get to the blood donation volume of 500 ml, multiply by 0.96 to correct for the non-caloric heme portion of the hemoglobin molecules, then multiply by 4 to get to calories.

  But wait! Hemoglobin is only 90 percent of the dry weight of RBCs. Multiply 1/10 the amount of the hemoglobin weight in 500 ml by 6, and add that to red blood cell calories.

• 5

  Estimate calories for the other types of cells. Of the 500 ml blood donation, roughly 1 percent will be white blood cells and platelets. Figure 5 g, multiplied by 1/3 to get to dry weight, times 6, to get to an estimated 10 calories. You'll multiply by 6 because some of the dry weight is protein or carbohydrates; both are 4 calories per gram, and some is fat, which is 9 calories per gram.

• 6

  Add everything up. Plasma protein, carbohydrates and fat, plus red cell and white cell contributions, should be approximately 425 calories for women and 460 for men. Anemia would result in a lower value. Use of EPO, a drug unethical athletes can use to increase their red blood cell count and thus their oxygen transporting capacity, would result in a higher value.