Dietary Intake Can Predict and Protect Against Changes in Bone Metabolism during Spaceflight and Recovery (Pro K) - 01.15.14
ISS Science for Everyone
Science Objectives for Everyone
The Dietary Intake Can Predict and Protect Against Changes in Bone Metabolism during Spaceflight and Recovery (Pro K) investigation is NASA's first evaluation of a dietary countermeasure to lessen bone loss of astronauts. Pro K proposes that a flight diet with a decreased ratio of animal protein to potassium will lead to decreased loss of bone mineral. Pro K has impacts on the definition of nutritional requirements and development of food systems for future exploration missions, and could yield a method of counteracting bone loss that would have virtually no risk of side effects.
Science Results for Everyone
OpNom Pro K
Johnson Space Center, Human Research Program, Houston, TX, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
October 2009 - March 2015
Previous ISS Missions
Pro K began operations during ISS Expeditions 21/22.
- The Dietary Intake Can Predict and Protect Against Changes in Bone Metabolism During Spaceflight and Recovery (Pro K) experiment tests the hypothesis that a diet with a decreased ratio of animal protein to potassium leads to decreased loss of bone mineral during flight. The specific goal for the study is to test this hypothesis by determining if the ratio of acid (animal protein) to base (potassium) precursors in the diet is correlated with bone metabolism and bone loss after space flight.
- Pro K could result in a dietary countermeasure for bone loss that has virtually no risk of side effects, no additional materials that would contribute to launch mass, and no additional crew time necessary during flight.
Though the mechanism of bone mineral loss associated with space flight is not completely understood, it likely involves multiple factors. The Dietary Intake Can Predict and Protect Against Changes in Bone Metabolism During Spaceflight and Recovery (Pro K) experiment studies the role of dietary intake patterns as one of these factors associated with bone mineral loss in space flight. The protocol is designed to evaluate the influence of acid and base precursors in the diet. The concept that diet can alter acid-base balance in the body is not new, and it is also well documented that a decrease in blood pH caused by acidic products of metabolism (metabolic acidosis) negatively affects bone; particularly in ground-based analogs of space flight.
This protocol tests the hypothesis that the ratio of acid precursors to base precursors (specifically animal protein and potassium, respectively) in the diet predicts changes in the loss of bone mineral during space flight and recovery. In two preflight and four inflight sessions, the ratio of animal protein to potassium in the diet is controlled during 4-day periods. In one inflight and 3 postflight sessions, the crewmember's self-selected diet is monitored over 4 days. The sessions in which diet is controlled or monitored allow researchers to evaluate the effects of diet on bone loss and on bone recovery following flight.
If successful, the study could lead to improvements in bone health during space flight, including development of a countermeasure that is virtually risk free and requires no additional stowage, crew time, power, or other constrained resources.
If successful, the study could lead to improvements in bone health during space flight, with use of a countermeasure that requires no additional stowage, crew time, power, or other constrained resources.
Given the growing trend in the United States toward diets high in animal protein, the proposed research has direct public health significance.
Samples are collected from 16 crewmembers. Sample sessions occur on flight days 15 (± 5 days), 30, 60, 120, and 180 (all ±14 days). If a mission is not exactly 180 days, the final session should be performed within 2 weeks of landing but greater than 3 weeks from previous session. Samples are returned to Earth for analysis within a year of the sampling date.
During flight, crewmembers consume foods from a prescribed diet (with either a high or a low ratio of animal protein to potassium), during which time they draw blood and collect urine samples. This is repeated five times throughout the mission. The blood samples are processed in the refrigerated centrifuge and then stored in the MELFI. Urine is collected void by void for 24 hours and the samples are stored in the MELFI during dietary intake sessions. Urine pH is measured daily.
The protocol comprises these steps:
- Provision of 4-day controlled or monitored diet sessions with collection of blood and urine samples before, during, and after flight.
- Biochemical analysis of these samples, in large part at the Johnson Space Center, using standard laboratory methods.
- Statistical analysis of the analytical results to evaluate the relationship of diet to markers of bone mineral loss over time.
Ground Based Results Publications
Zwart SR, Davis-Street JE, Paddon-Jones D, Ferrando AA, Wolfe RR, Smith SM. Amino acid supplementation alters bone metabolism during simulated weightlessness. Journal of Applied Physiology. 2005; 99: 134-40.
Zwart SR, Hargens AR, Smith SM. Animal protein and potassium intakes are predictors of bone resorption in spaceflight analogs and in ambulatory subjects. American Journal of Clinical Nutrition. 2004; 80: 1058-65.
Zwart SR, Smith SM. The impact of space flight on the human skeletal system and potential nutritional countermeasures. International SportMed Journal. 2005; 6(4): 199-214.
Smith SM, Zwart SR, Heer MA, Lee SM, Baecker N, Meuche S, Macias BR, Shackelford LC, Schneider SM, Hargens AR.WISE-2005: Supine Treadmill Exercise within Lower Body Negative Pressure and Flywheel Resistive Exercise as a Countermeasure to Bed Rest-Induced Bone Loss during 60-Day Simulated Microgravity in Women. Bone. 2008; 42(572-81): 572.
Smith SM, Zwart SR, Kloeris VA, Heer MA. Nutritional Biochemistry of Space Flight.. Happauge, NY: Nutritional Biochemistry of Space Flight; 2009.
Human Adaptation and Countermeasures Division
NASA Image: ISS030E033506 - View of PRO-K Food Container Contents.
+ View Larger Image