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Hydration of fat-free mass in healthy women with special reference to the effect of pregnancy
Linköping University, Department of Biomedicine and Surgery, Nutrition. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Biomedicine and Surgery, Nutrition. Linköping University, Faculty of Health Sciences.
2004 (English)In: American Journal of Clinical Nutrition, ISSN 0002-9165, E-ISSN 1938-3207, Vol. 80, no 4, 960-965 p.Article in journal (Refereed) Published
Abstract [en]

Background: Knowledge of the biological variability of the hydration factor (HF), ie, the ratio between total body water and fat-free mass, is important when calculating total body fat by means of the commonly used two-component model, which is based on estimates of body weight and total body water. The effect of pregnancy on the biological variability of HF, and consequently on the precision of the two-component model, is unknown.

Objective: Our goal was to assess the effect of pregnancy on HF and its biological variability.

Design: HF was assessed in 33 women planning pregnancy and in 17 of these women during gestational weeks 14 and 32 and 2 wk postpartum. HF was calculated by using estimates of body weight, total body water obtained by means of deuterium dilution, and body volume measured by using underwater weighing.

Results: In the 17 women who became pregnant, HF was 0.718 ± 0.023, 0.723 ± 0.031, 0.747 ± 0.017, and 0.734 ± 0.020 before pregnancy, in gestational week 14, in gestational week 32, and 2 wk postpartum, respectively. The biological variability represented ≈2% of average HF in the nonpregnant state. The corresponding figure was >3% in gestational week 14 but ≤1.7% in gestational week 32.

Conclusion: The two-component model for assessing body fat is as appropriate during late gestation as it is in the nonpregnant state, although its precision may be impaired when applied during the first part of pregnancy.

Place, publisher, year, edition, pages
2004. Vol. 80, no 4, 960-965 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-23923PubMedID: 15447906Local ID: 3471OAI: oai:DiVA.org:liu-23923DiVA: diva2:244238
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
In thesis
1. Studies on energy metabolism and body composition of healthy women before, during and after pregnancy
Open this publication in new window or tab >>Studies on energy metabolism and body composition of healthy women before, during and after pregnancy
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Current recommendations propose that an entire pregnancy requires an additional amount of energy from the diet equivalent to 335 000 kJ. This figure is mainly based on increases in the basal metabolic rate (BMR) and retention of total body fat (TBF). The BMR response to pregnancy varies considerably among women, but the factors responsible for this variability are unknown. TBF can be calculated from total body water (TBW) and the hydration factor (HF), using the so-called two-component model. However, the validity of this model during pregnancy has been questioned. Furthermore, current recommendations propose that energy needs during pregnancy may be partly offset by reductions in physical activity, but this statement is supported by little experimental evidence. The aims of this thesis were: to evaluate if the physical activity level (PAL) can be estimated by means of heart rate recording, accelerometry, and a questionnaire in women planning pregnancy; to assess the effect of pregnancy on energy expenditure due to physical activity, on activity pattern and on the biological variability of HF; to evaluate the use of bioimpedance spectroscopy (BIS) for assessing TBW during pregnancy; and to identifY factors explaining the variability of the BMR response to pregnancy.

Healthy women were studied before pregnancy (n=38), and in gestational weeks 8, 14, 20, 32, 35 and 2 weeks post partum (n=23). Total energy expenditure (TEE), BMR, TEE/BMR, activity pattern, body composition, circulatory variables and serum levels of thyroid hormones and insulin growth factor-I (IGF-1) were measured. Foetal weight in gestational week 31 and infant birth weight were assessed.

All estimates of PAL were imprecise and too low in women planning pregnancy. There was little change in TEE/BMR in gestational week 14, but it was significantly reduced in gestational week 32. However, activity pattern was largely unaffected by pregnancy. The biological variability of HF was 2%, 3% and 1.7% or less of average HF before pregnancy and in gestational weeks 14 and 32, respectively. BIS underestimated TBW during pregnancy. In gestational week 14, the increase in BMR correlated significantly with the increase in body weight and with TBF (%)before pregnancy. Together these variables explained about 40% of the variability in the BMR response. In gestational week 32, the increase in BMR correlated significantly with changes in body weight, TBF, fat-free mass, IGF-I, cardiac output and free triiodothyronine. At this stage of gestation the increase in body weight in combination with foetal weight or with the increased levels of IGF-I in serum explained about 60% of the variability of the increased BMR.

In conclusion: I) Heart rate recording, accelerometry and the questionnaire produced inappropriate PAL estimates. 2) In women maintaining their pre-pregnant activity pattern the increase in BMR represents the major component of the increased energy expenditure during pregnancy. 3) The two-component model for assessing TBF is appropriate in late gestation, while its precision may be impaired in early pregnancy. 4) BIS in its present form is not appropriate for assessing TBW during pregnancy. 5) Nutritional factors are important regarding the variability in the BMR response to pregnancy.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. 58 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 853
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-23970 (URN)3520 (Local ID)91-7373-825-5 (ISBN)3520 (Archive number)3520 (OAI)
Public defence
2004-05-28, Aulan, Hälsans Hus, Hälsouniversitetet, Linköping, 13:00 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2012-10-31Bibliographically approved

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