TABLE 5.

Results of 2 linear mixed-effects models investigating the relation between changes in astronaut urinary calcium and HPK and LPK diets relative to a monitored diet¹

	Pre- and in-flight model				In-flight model
	Estimate	SE	t	P value	Estimate	SE	t	P value
Measure
Intercept	−4.86	6.23	−0.8	0.44	2.04	6.56	0.3	0.76
HPK diet	−0.29	1.00	−0.3	0.77	−1.08	0.83	−1.3	0.21
LPK diet	0.96	0.71	1.4	0.19	−1.33	0.75	−1.8	0.08
Body weight, kg	−0.05	0.05	−1.1	0.27	−0.02	0.05	−0.3	0.76
Female	−0.63	1.54	−0.4	0.68	−0.71	1.66	−0.4	0.67
Age, y	0.08	0.10	0.8	0.45	0.06	0.11	0.6	0.58
Energy, kcal/d	0.00	0.00	0.2	0.85	0.00	0.00	0.5	0.66
NEAP, mEq/d	−0.01	0.02	−0.6	0.57	0.00	0.02	−0.1	0.94
Dietary sulfur, mEq/d	0.01	0.03	0.3	0.78	−0.02	0.03	−0.5	0.65
Dietary sodium, mg/d	0.001	0.00	2.5	0.02	0.001	0.00	2.8	0.01
Dietary fiber, g/d	−0.07	0.04	−1.6	0.12	−0.08	0.04	−1.8	0.09
Flight day	0.02	0.00	4.2	<0.001	−0.02	0.00	−3.8	<0.01
In-flight status	3.86	0.61	6.4	<0.0001	—	—	—	—
Flight day × in-flight status	−0.02	0.00	−5.6	<0.0001	—	—	—	—
Exercise, lb lifted	—	—	—	—	0.00	0.00	−1.0	0.31
Mean CO2, mm Hg	—	—	—	—	0.08	0.29	0.3	0.78
Random effects
σastronaut	2.0				2.1
σ	1.2				1.1

¹Changes and percentage changes in urinary calcium concentration (Table 2) were measured between each 4-d controlled-diet session and the Pre (L–10) session, when crew members were not on a controlled diet. The preflight and in-flight model controlled for body weight; sex; age; energy; NEAP; dietary sulfur, sodium, and fiber; flight day; and in-flight status. The in-flight model controlled for exercise (cumulative resistive exercise for 3 wk before data collection) and mean CO₂. n = 17. HPK, high animal protein:potassium ratio; LPK, low animal protein:potassium ratio; NEAP, net endogenous acid production; Pre (L–X), X days before launch.