I am sure I have read articles about energy expenditure during  lactation in
nurtition journals - I am looking now and here is the first one I found.
Sincerely, Toby Gish RN,INCLC

American Journal of Clinical Nutrition, Vol. 69, No. 2, 299-307, February
1999
© 1999 American Society for Clinical Nutrition


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      Original Research Communications

Adjustments in energy expenditure and substrate utilization during late
pregnancy and lactation1,2,3,4
Nancy F Butte, Judy M Hopkinson, Nitesh Mehta, Jon K Moon and E O'Brian
Smith

Background: Metabolic adjustments occur during pregnancy and lactation to
support fetal growth and milk synthesis; however, the effect of body
composition and hormonal milieu on these changes is poorly understood.

Objective: We hypothesized that energy metabolism changes during pregnancy
and lactation to support fetal growth and milk synthesis, and that body
composition and hormonal milieu influence these alterations.

Design: We measured energy expenditure, body composition, and hormone,
metabolite, and catecholamine concentrations in 76 women (40 lactating, 36
nonlactating) at 37 wk gestation and 3 and 6 mo postpartum. Total energy
expenditure (TEE), basal metabolic rate (BMR), sleeping metabolic rate
(SMR), and minimal SMR (MSMR) were measured with room calorimetry. Fat-free
mass (FFM) and fat mass were estimated with a 4-component model.

Results: TEE, BMR, SMR, and MSMR were 15-26% higher during pregnancy than
postpartum after being adjusted for FFM, fat mass, and energy balance. TEE,
SMR, and MSMR were higher in lactating than in nonlactating women. Fasting
serum insulin, insulin-like growth factor I, fatty acids, and leptin, and
24-h urinary free norepinephrine, epinephrine, and dopamine correlated
positively with TEE, BMR, SMR, and MSMR. In nonlactating women, the
respiratory quotient decreased over time, carbohydrate oxidation decreased,
and fat oxidation increased. Substrate utilization was not influenced by
body composition, fasting serum hormones, or 24-h urinary catecholamines.

Conclusions: These results indicate increased energy expenditure and
preferential use of carbohydrates during pregnancy and lactation. Elevated
respiratory quotient and carbohydrate utilization during pregnancy continue
during lactation, consistent with preferential use of glucose by the fetus
and mammary gland.


Key Words: Energy expenditure . basal metabolic rate . sleeping metabolic
rate . substrate oxidation . pregnancy . lactation . breast-feeding .
resting energy expenditure . resting metabolic rate . fat oxidation . lipid
oxidation . carbohydrate oxidation . women

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