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Biomedical subjects

A M Prentice

Publications and source records attributed to A M Prentice.

At least 145 records · Page 8Linked to original sources
PubMed1988

Energy expenditure from minute-by-minute heart-rate recording: comparison with indirect calorimetry.

Total daily energy expenditure (TDEE) and energy expended in activity (EAC) were estimated by the minute-by-minute heart-rate method in 22 (16 men, 6 women) individually calibrated subjects and compared with values obtained by whole-body indirect calorimetry. Subjects followed four activity protocols during the 22 h in the calorimeter; no exercise (n = 6) and 2 (n = 5), 4 (n = 4), and 6 (n = 6) 30-min bouts of exercise on a bicycle ergometer at varying intensities. There were no statistically significant differences between the two methods in TDEE or EAC in any of the sex or protocol groupings. The regression of TDEE by heart rate on TDEE in the calorimeter was y = 0.92x + 1.0 MJ; (r = 0.87, SEE = 0.91 MJ). The heart-rate method also follows the varying activity patterns of individuals and can be used to closely estimate the TDEE and EAC of even small (n = 4-6) groups of subjects. In the present measurements, it gave a maximum error of TDEE for individuals of +20% and -15%.

Adult↗
PubMed1988

Overnight and basal metabolic rates in men and women.

The FAO/WHO/UNU recommendations for energy requirements assume that the energy cost of sleep is equal to the basal metabolic rate (BMR). We have tested the validity of this assumption by analysing overnight and BMR measurements made by whole-body indirect calorimetry. Data from 80 healthy subjects measured on a total of 246 occasions have been used. In a subgroup of 40 normal lean subjects the mean ratio of overnight metabolic rate (Overnight MR): BMR was 0.95 (range 0.85 - 1.02, s.d. 0.04). The mean ratio of lowest sleeping metabolic rate (Lowest SMR): BMR was 0.88 (range 0.83 - 0.96, s.d. 0.04). Ratios of Overnight MR: BMR were not significantly affected by different levels of exercise on the preceding day. This ratio was significantly higher for subjects who were obese, late pregnant or attached to ECG electrodes. With the exception of the late pregnant subjects these groups had the same Lowest SMR:BMR ratios as the normal lean subjects, indicating that the higher Overnight MR was caused by disturbed sleep. The data suggest that the use of BMR to estimate overnight energy expenditure would introduce an average overestimate of approximately 5 per cent during the actual hours of sleep, but that when applied over 24 h the error becomes negligible.

Adult↗
PubMed1987

Intra-individual variability and measurement noise in estimates of energy expenditure by whole body indirect calorimetry.

1. Four men were each studied continuously over 12 d in a whole-body calorimeter. Dietary intake and daily activities were kept constant throughout the study. 2. Day-to-day coefficients of variation in energy expenditure within subjects were found to be 1.97% over 24 h, 5.93% during basal metabolic rate measurement, 2.40% overnight and 3.22% in exercise. 3. The contribution of measurement system noise to the observed variability was analysed and shown to be generally small. The source of this noise was considered. 4. The results reinforce and extend other comparable reports and show that within-subject variability forms a small part of reported observations of between-subject variability.

Adult↗
PubMed1987

Increased birthweight after prenatal dietary supplementation of rural African women.

Birthweight data from 197 rural Gambian women who received an energy-dense prenatal dietary supplement over a 4-y period (net intake = 430 kcal/d) was compared with data from 182 women from 4 baseline years. Preintervention birthweights averaged 2944 +/- 43 (SEM) g when women were in positive energy balance during the dry harvest season (pregnancy weight gain greater than 1200 g/mo). Birthweights decreased to 2808 +/- 41 g (p less than 0.01) in the wet season when food shortages and agricultural work caused negative energy balance (weight gain less than 500 g/mo). There were no detectable secular trends in the baseline data. Supplementation was ineffective during the dry season but highly effective during the wet season: +225 +/- 56 g, p less than 0.001 (unadjusted) or +200 +/- 53 g, p less than 0.001 (adjusted for sex, season, and parity) by between-child multiple regression analysis; +231 +/- 65 g, p less than 0.001 by within-mother analysis. The proportion of low-birthweight babies (less than 2501 g) decreased from 23.7-7.5%, p less than 0.002. The observed threshold effect emphasizes the importance of selective targeting of interventions to truly at-risk groups.

Anthropometry↗
PubMed1986

High levels of energy expenditure in obese women.

Total free living energy expenditure was compared in lean and obese women by the new doubly labelled water method and partitioned into basal metabolism and thermogenesis plus activity by whole body calorimetry. Average energy expenditure was significantly higher in the obese group (10.22 versus 7.99 MJ/day (2445 versus 1911 kcal/day); p less than 0.001) resulting from an increase in the energy cost of both basal metabolism and physical activity. Self recorded energy intakes were accurate in the lean subjects but underestimated expenditure by 3.5 MJ/day (837 kcal/day) in the obese group. Basal metabolic rate and energy expenditure on thermogenesis plus activity were identical in the two groups when corrected for differences in fat free mass and total body mass. In the obese women in this series there was no evidence that their obesity was caused by a metabolic or behavioural defect resulting in reduced energy expenditure.

Activities of Daily Living↗
PubMed1986

Maternal nutrition and breast feeding.

In this short review we will first summarize current theories relating to maternal nutritional needs during human lactation, then deal with dietary situations where theory and experimental findings differ. In fact such a divergence occurs most of the time, both in affluent countries and especially in the Third World. We will then consider the various hypotheses which are currently being tested in an attempt to rationalize this complex but crucially important enigma. These hypotheses suggest that the mother can 'adapt' both physiologically and behaviourally in order to protect the adequate nutrition of her baby. Finally we will discuss the health significance of what happens when the mother's ability to accommodate the nutritional stresses of pregnancy and lactation fails. Although we have been asked to deal just with lactation, from time to time it will also become necessary to consider events occurring during pregnancy in order to place the nutritional stresses of lactation within a rational biological perspective. Whilst in the medical world, parturition tends to be a watershed event which divides one clinical specialty from another, in nutritional terms its main significance is merely that the mother switches feeding her baby from one part of her anatomy to another. In so far as her nutritional requirements are concerned pregnancy and lactation are part of the same continuum.

Adaptation, Physiological↗
PubMed1986

Use of food quotients to predict respiratory quotients for the doubly-labelled water method of measuring energy expenditure.

A method is proposed for estimating the respiratory quotients (RQ) required in the calculation of free-living energy expenditure measured by the doubly-labelled water technique in man. Worked examples show that, in most normal subjects, measured or predicted food quotients (FQ) can be used in place of RQs since energy balance is usually maintained over the 10-20-d periods of double-isotope measurements. Examples of observed FQs in the UK are: omnivorous adults, 0.845 +/- 0.013 (s.d.); vegetarians, vegans and Asian immigrants, 0.860-0.880; breast-fed infants, 0.835 rising to 0.870 as weaning progresses; bottle-fed infants, 0.840-0.880. Alcohol intakes in excess of 2-3 per cent of total energy lower the FQ value. In most communities in the developing world FQs are substantially higher (0.900-0.955) due to the low contribution of fat to overall energy intakes; but FQs decrease progressively as the diet becomes more westernized. In the UK the between- and within-subject coefficients of variation based on 4-d weighed intakes are only 1.5 and 0.7 per cent respectively. A single 4-d measurement of dietary composition can therefore be used to predict a subject's FQ. In subjects in energy imbalance (eg, during growth, illness or when dieting) errors in calculated energy expenditure will rarely exceed 3-5 per cent even if the imbalance is ignored; in practice anabolism or catabolism can be accounted for and the FQ adjusted when converting FQ to RQ. The error incurred due to the substitution of adjusted FQ for RQ in the doubly-labelled water method will usually be negligible and should never exceed +/- 2 per cent.

Alcohol Drinking↗
PubMed1986

Folate status during pregnancy and lactation in a West African rural community.

Red cell folate concentration was used to measure folate status in 89 rural Gambian women, 81 of whom were pregnant or lactating for the duration of the study. During pregnancy, the women received a haematinic supplement of 500 micrograms pteroyl glutamic acid and 47 mg iron a day, and a food supplement was also given to some of the women during either pregnancy, or lactation, or both. During pregnancy, the red cell folate levels reached a peak around the fifth month, attributable to the haematinic supplement. By the third month of lactation they had fallen back to a low plateau, which was below the accepted lower limit of normality in 56 per cent of those who did not receive a food supplement during lactation. In addition to these changes, there was a significant cyclical variation with season, peak values occurring in the rainy season. Plasma iron values followed the red cell folate patterns quite closely. Changes in blood haemoglobin levels during pregnancy were similar to those reported from other communities; there was also an increase in mean red cell volume during the first half of pregnancy, reaching a peak at the same stage as the peaks of red cell folate and plasma iron. There was no indication of the presence of raised cell volumes in association with low folate indices which might suggest megaloblastosis. It is concluded that the 500 micrograms daily folate supplement is both necessary and adequate to maintain red cell folate levels during pregnancy in this community, but that in the absence of further supplements during lactation, red cell folate levels will fall to undesirably low levels in many subjects by the third-to-sixth month of lactation.

Adolescent↗
PubMed1985

Unexpectedly low levels of energy expenditure in healthy women.

A new method for measuring total energy expenditure (TEE) with stable isotopically labelled water (2H218O) was used to measure average daily energy expenditure over 14-21 day periods in 12 healthy women following their normal activity patterns. TEE expressed as a multiple of basal metabolic rate (TEE/BMR) averaged only 1 X 38 +/- 0 X 04. This result is at variance with the widely held assumption that minimum maintenance requirements are 1 X 5 times BMR.

Adult↗
PubMed1985

Mastitis in rural Gambian mothers and the protection of the breast by milk antimicrobial factors.

Mastitis was found to be a sizeable clinical problem in a group of lactating Gambian mothers. The mean monthly incidence was 2.6% and repeated episodes of mastitis were common. The role of milk antimicrobial factors in the local defence of the breast against mastitis was investigated by analysis of IgA, IgG, IgM, C3, C4, lactoferrin and lysozyme in the breast milk of 10 mastitis patients. Acute inflammation of the breast was accompanied by the rapid appearance of high concentrations of serum-derived immunoproteins in mastitic milk. Changes in the milk levels of lactose, sodium and transferrin indicated that this was due to a temporary opening of the paracellular pathway. Concentrations of secretory immunoproteins (IgA, lactoferrin and lysozyme) exhibited a delayed response, being elevated one week after the attack of mastitis. The normal milk of mastitis sufferers was significantly deficient in IgA, C3 and lactoferrin when compared with other lactating women suggesting that the former were predisposed to mastitis.

Complement C3↗
PubMed1984

Seasonal variations in plasma retinol and carotenoid levels in rural Gambian women.

Plasma carotenoid levels exhibited a major seasonal variation in pregnant and lactating women in Keneba, a rural Gambian village. This is probably due mainly to the seasonally related contribution of mangoes, which are a major dietary component during May and June, but are essentially unavailable for the remainder of the year. Plasma retinol levels, on the other hand, exhibited much less seasonal variation, although a trend towards higher levels in May and June was just discernible. Plasma retinol levels were significantly lower than those observed in a group of pregnant and lactating women living in the UK.

Carotenoids↗
PubMed1984

The effect of water abstention on milk synthesis in lactating women.

The effects of dehydration on mechanisms of water balance and milk synthesis were investigated in ten lactating Gambian women who were fasting during Ramadan. Ten non-pregnant, non-lactating women acted as controls. Fasting consisted of total water abstention from 05.00 hours to 19.30 hours and was accompanied by high insensible water losses. Lactating women lost 7.6% of their total body water between 07.00 hours and 19.00 hours. Control subjects lost significantly less. Plasma indices of dehydration (osmolality, sodium, uric acid) showed a greater rise in the lactating women than in the control subjects over the period of fasting. However, the 19.00 hours values remained in the normal range obtained on non-Ramadan days. During Ramadan the lactating women restricted their urinary output to a lesser degree than the controls, and for much of the day their urine was also less concentrated. The lactating women appeared to have adapted by superhydrating themselves overnight. This resulted in very low urine concentrations (osmolality, sodium, urea, creatinine) in morning samples. Urine concentrations approached, but did not exceed, non-Ramadan levels by late afternoon. The daily water turnover of 6.4 litres in the lactating women was 2 litres greater than in the controls. This difference was much greater than that required for milk synthesis (500 ml) and may represent a further protective mechanism. Fasting caused changes in milk osmolality, lactose, sodium and potassium concentrations indicative of a marked disturbance of milk synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Unilateral breast dysfunction in lactating Gambian women.

Approximately 3% of lactating women in a rural Gambian village displayed long-term unilateral breast dysfunction as evidenced by abnormal milk composition and virtual cessation of suckling by the infant. This paper presents case histories of four such women studied over two successive lactations. The average breast-milk output of these women did not differ significantly from the mean value for the remainder of the community, indicating that the non-affected breast was usually able to compensate for the dysfunction. This was confirmed by the fact that the child-rearing record of three of the four women was better than the community average. In two of the women the breast which was dysfunctioning in one lactation reverted completely to normal for the next lactation. It is suggested that in such cases the dysfunction is self-perpetuating and may be alleviated by counselling mothers to persevere with feeding from the affected breast.

Adult↗
PubMed1984

The effect of improved nutrition on plasma prolactin concentrations and postpartum infertility in lactating Gambian women.

A substantial increase in food consumption of lactating Gambian women has been shown to be associated with a reduction in their plasma prolactin concentration. Women receiving food supplements during pregnancy as well as in lactation exhibited an even greater lowering of the postpartum plasma levels of this hormone. Consequently prolactin values of supplemented women returned more quickly to levels which allowed the resumption of menstrual and ovulatory activity. Concurrent measurements of the plasma concentrations of estradiol and progesterone in addition to prolactin allowed the calculation of prolactin values at which half the lactating women could be expected to have resumed menstruation and ovulation. These values were 1007 and 759 microU/ml, respectively. Dietary improvement during lactation alone resulted in these critical prolactin concentrations being reached 21 wk earlier than in nonsupplemented counterparts, while those receiving the extra food in both pregnancy and lactation showed a 35-wk shortening of postpartum amenorrhea and infertility.

Amenorrhea↗