TABLE 4.

Results of 2 linear mixed-effects models investigating the relation between changes in astronaut serum BSAP 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	−3.7	12.9	−0.3	0.77	−9.0	12.3	−0.7	0.47
HPK diet	−2.7	3.8	−0.7	0.48	4.1	2.9	1.4	0.17
LPK diet	−5.0	2.6	−1.9	0.06	1.9	2.6	0.7	0.48
Body weight, kg	−0.1	0.1	−1.1	0.28	−0.1	0.1	−0.9	0.40
Female	−3.9	2.9	−1.4	0.17	−2.5	2.9	−0.9	0.38
Age, y	0.3	0.2	1.5	0.15	0.1	0.2	0.7	0.49
Energy, kcal/d	0.0	0.0	−0.8	0.41	0.0	0.0	−1.1	0.30
NEAP, mEq/d	−0.1	0.1	−1.8	0.08	0.0	0.1	−0.5	0.61
Dietary sulfur, mEq/d	0.1	0.1	0.8	0.45	0.0	0.1	−0.2	0.82
Dietary sodium, mg/d	0.0	0.0	−0.2	0.83	0.0	0.0	1.3	0.19
Dietary fiber, g/d	−0.1	0.2	−0.5	0.61	0.0	0.2	0.1	0.94
Flight day	−0.1	0.0	−6.3	<0.0001	0.1	0.0	7.1	<0.001
In-flight status	5.4	2.4	2.3	0.02	—	—	—	—
Flight day × in-flight status	0.1	0.0	8.0	<0.0001	—	—	—	—
Exercise, lb lifted	—	—	—	—	0.0	0.0	0.6	0.54
Mean CO2, mm Hg	—	—	—	—	3.0	1.1	2.7	0.01
Random effects
σastronaut	2.9				2.6
σ	4.6				4.3

¹Changes and percentage changes in BSAP 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 CO₂. n = 17. BSAP, bone-specific alkaline phosphatase; HPK, high animal protein:potassium ration; LPK, low animal protein:potassium ration; NEAP, net endogenous acid production; Pre (L–X), X days before launch.