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Biomedical subjects

A M Prentice

Publications and source records attributed to A M Prentice.

At least 91 records · Page 5Linked to original sources
PubMed1995

Sugar and body weight regulation.

The need to understand reasons for the high prevalence of obesity in developed countries has led to examination of dietary habits that may contribute to obesity. We consider whether consumption of high amounts of sugars presents a public health problem by contributing to the development of obesity. Metabolic studies show that diets high in fat are more likely to result in body fat accumulation than are diets high in carbohydrate. There is no indication that simple sugars differ from complex sugars in this regard. Epidemiologic data show a clear inverse relation between intake of sugar and fat. Further, although high intake of dietary fat is positively associated with indexes of obesity, high intake of sugar is negatively associated with indexes of obesity. There is ample reason to associate high-fat diets with obesity but, at present, no reason to associate high-sugar diets with obesity.

Body Weight↗
PubMed1995

Covert manipulation of dietary fat and energy density: effect on substrate flux and food intake in men eating ad libitum.

This study assessed whether human food intake is regulated by negative feedback, directly or indirectly, from carbohydrate stores (glycogenostatic model). Six men were studied on three occasions during 7 d of whole-body indirect calorimetry, throughout which they had ad libitum access to one of three covertly manipulated diets: low fat (20% of energy as fat, 67% of energy as carbohydrate, and 13% of energy as protein; 4.80 kJ/g; LF), medium fat (40% of energy as fat, 47% of energy as carbohydrate, and 13% of energy as protein; 5.59 kJ/g; MF), or high fat (60% of energy as fat, 27% of energy as carbohydrate, and 13% of energy as protein; 7.04 kJ/g; HF). Energy intakes increased with percent fat (F[92,60] = 36.7; P < 0.001), producing average daily balances of -0.27, 0.77, and 2.58 MJ/d during the LF, MF, and HF diets, respectively. Changes in carbohydrate stores were attenuated by autoregulatory changes in carbohydrate oxidation. Carbohydrate balance showed a negative relation to the subsequent day's energy balance (t = 2.696; P = 0.0082) but explained only 5.5% of the variance. The relation for fat was positive (t = 5.245; P < 0.0001), accounting for 19.9% of the variance (stepwise regression). LF, lower-energy diets are more satiating than are HF-higher-energy diets, but carbohydrate stores per se did not entirely account for the change that diet composition had on energy intake. This study suggests that protein and carbohydrate have potential to reduce subsequent energy intake whereas there was no apparent reductive effect due to fat.

Adult↗
PubMed1995

Covert manipulation of the ratio of dietary fat to carbohydrate and energy density: effect on food intake and energy balance in free-living men eating ad libitum.

We previously increased the energy density and fat content across three diets (factorial design), which led to a marked increase in energy intake in six men over 7 d while continuously resident in a whole-body indirect calorimeter. In the present study we fed the same diets to seven men who were resident in, but not confined to, a metabolic suite for 2 wk/diet. This added a component of increased physical activity. The fat, carbohydrate, and protein contents, respectively, of each diet (as a percent of energy) were as follows: low-fat (LF), 20:67:13; medium-fat (MF), 40:47:13; and high-fat (HF), 60:27:13. Energy density increased as the percent of fat in the diet increased. Energy intakes from the LF, MF, and HF diets (9.11, 10.32, and 12.78 MJ/d, respectively) were almost identical to those in our calorimeter study (9.02, 10.2, and 12.35 MJ/d, respectively) whereas energy expenditures (estimated by the doubly labeled water method) were 12.45, 12.10, and 11.97 MJ/d on the LF, MF and HF diets, respectively, compared with 9.48, 9.53, and 9.78 MJ/d, respectively, in our calorimeter study. This finding suggests that diet composition and energy expenditure combined influence energy balance in humans.

Adult↗
PubMed1995

Effects on metabolic rate and fuel selection of a selective beta-3 agonist (ICI D7114) in healthy lean men.

METHOD: ICI D7114 is a selective beta-3 agonist which in some animals increases metabolic rate, promotes weight loss and improves glucose tolerance. To investigate its potential usefulness in humans, 16 healthy young men (mean age 28.9 +/- 8.0 years; body mass index 22.5 +/- 1.6 kg/m2) were given ICI D7114 (150 mg/day, 2.08 +/- 0.24 mg/kg body weight) or placebo for 14 days in a double-blind randomised parallel group trial. Energy expenditure (EE) and substrate oxidation were assessed by continuous whole-body indirect calorimetry on Day 0 (before dosing), on day 1 (acute effect) and on Day 14 (chronic effect). RESULTS: Analysis of covariance indicated no significant effects on EE 4 h post-dose (Day 1, +2.4%, NS; Day 14, +1.0%, NS). There was no chronic effect on either the lowest 1 h of sleeping EE (+2.2%, NS) or 24 h EE (+0.7%, NS). There was a marginally significant chronic stimulation of basal metabolic rate (+3.6%, P = 0.042). ICI D7114 had no significant influence on protein, fat or carbohydrate oxidation. Tolerability and safety data showed that there were no increases in resting heart rate or blood pressure; no change in plasma potassium or reports of tremor; no haematological or biochemical abnormalities and no adverse events. CONCLUSION: We conclude that over 14 days ICI D7114 at a dose level of 150 mg/day has no biologically significant effect on EE in healthy, lean men.

Adolescent↗
PubMed1994

Energy-sparing strategies to protect human fetal growth.

OBJECTIVES: Our purpose was to test whether energy-sensitive adjustments in gestational metabolism, previously observed in studies of Gambian and British women, are a general phenomenon and to define the nutritional factors that direct them. STUDY DESIGN: Retrospective analysis of data on basal metabolic rate and fat deposition in 360 pregnancies from 10 studies in a wide range of nutritional settings was performed. RESULTS: The energy costs of pregnancy varied widely between different communities: maintenance costs from -45 to +210 MJ, fat deposition from -23 to +267 MJ, and total energy costs from -20 to +523 MJ. Total costs were correlated with prepregnancy fatness (r = 0.80, p < 0.01) and pregnancy weight gain (r = 0.94, p < 0.001). Marginally nourished women conserved energy by suppressing metabolic rate and by gaining little fat. CONCLUSIONS: The energy needs of pregnancy are modulated over a wide range in response to maternal energy status. This may be an important means of protecting fetal growth.

Adipose Tissue↗
PubMed1994

Effect of alcohol on postmeal fat storage.

Energy expenditure and macronutrient balances were assessed in normal healthy men by whole-body indirect calorimetry after meals consumed with and without ethanol to test the theory that alcohol energy is not fully available because of futile cycling. Alcohol addition (A) or isoenergetic substitution (S) caused fat retention by significantly suppressing its oxidation when the alcohol was actively metabolized (0-6h). However, on protocol S, fat balance was later reestablished due to raised fat oxidation (6-20.5 h) secondary to a relative carbohydrate deficiency. On protocol A, fat balance remained significantly raised. The thermogenic effect of alcohol was similar to that of carbohydrate, providing no evidence for futile cycling. Short-term studies that fail to account for later readjustments of macronutrient balance can be misleading. We conclude that alcohol has a fat-sparing effect similar to that of carbohydrate and will only cause fat gain when consumed in excess of normal energy needs.

Adult↗
PubMed1994

Alterations in fuel selection and voluntary food intake in response to isoenergetic manipulation of glycogen stores in humans.

This study investigated the relative importance of alterations in carbohydrate intake or oxidation as mechanisms for rectifying extreme perturbations of glycogen stores. Six lean men were studied on three occasions in which a stabilization period (days 1 and 2) was immediately followed by whole-body indirect calorimetry (days 3-5). Glycogen stores were manipulated on days 3 and 4 by using isoenergetic diets providing carbohydrate at 79% (HC), 48% (MC), or 9% (LC) of energy. Free access to MC meals and snacks was allowed on days 5 and 6 outside the calorimeter. The manipulations caused large alterations in glycogen stores (HC, +206 g; MC, +132 g; LC, -121 g; HC vs LC, 327 g), but subsequent voluntary food intake was very similar across treatments (HC, 18.2 MJ/36 h; MC, 17.7 MJ/36 h; LC, 18.1 MJ/36 h, NS). Over days 3-5 the average difference in carbohydrate intake (HC vs LC) was 16.1 MJ (1010 g), but balances differed by only 1.7 MJ (110 g) because of autoregulatory changes in carbohydrate oxidation. These were the only significant mechanisms for reestablishing carbohydrate balance.

Adult↗
PubMed1994

Maternal and fetal determinants of adult diseases.

Recent epidemiologic studies in the United Kingdom have led to the hypothesis that adverse nutritional experiences in utero have a powerful influence on the development of degenerative diseases in adulthood. Poor fetal growth as measured by weight, length, head, chest, and abdominal circumferences is a strong predictor of hypertension, diabetes, hyperlipidemia, alteration in clotting factors, Syndrome X,* and mortality from cardiovascular and chronic obstructive airways disease. The theory of fetal origins of adult disease proposes that early defects in the development, structure, and function of organs lead to a programmed susceptibility, which interacts with later diet and environmental stresses to cause overt disease many decades after the original insult.

Birth Weight↗
PubMed1994

Body mass index and lactation performance.

Data from the world literature have been analysed in order to test whether low body mass index (BMI: kg/m2) is a useful indicator of functional impairment of lactation performance. Forty-one databases containing 1726 measurements have been identified as having reliable estimates of breast-milk quantity and/or quality. There is no detectable relationship between maternal BMI and the volume of milk produced by mothers when analysed according to the mean BMI of different populations, or of different subgroups stratified by BMI within populations. This conclusion holds even at BMIs < 18.5. The most remarkable feature of the data is the very high milk volumes produced by very thin mothers. It is accepted that the composition of breast milk is relatively unaffected by general undernutrition of the type that would be indicated by a low BMI with the possible exception of milk fat levels and hence the energy content. Analysis of the available data reveals studies in which there are weak, but significant, correlations between maternal BMI and milk fat. However, other studies show no association or even a negative relationship. Inter-country analysis fails to reveal any detectable association between BMI and milk energy. Milk energy levels seem adequate even at BMIs < 18.5. It is concluded that human lactation performance is extremely robust and that BMI does not provide a useful indicator of function at the levels studied so far. Lactation performance must become compromised when undernutrition is sufficiently severe, but it appears that this must occur only in famine or near famine conditions.

Body Mass Index↗
PubMed1994

Fatness in relation to substrate oxidation during exercise.

The aim of this study was to test the hypothesis that differences in fuel utilisation during exercise, determined by muscle fibre-type profile, are an aetiological factor for obesity as proposed by Wade et al. (Lancet 1990, 335, 805-8). An investigation was carried out of relationships between body fatness (assessed by skinfolds, densitometry and dual X-ray absorptiometry) and fuel utilisation represented by the respiratory exchange ratio (RER, assessed by indirect calorimetry) during three cycle ergometer exercises. Exercise 1 was an exact replication of the Wade protocol (fixed 100 Watt load and unstandardised with respect to antecedent diet and activity). Exercises 2 (fasted) and 3 (fed) were highly standardised and adjusted to represent the same relative workload for each subject (45% VO2max). The subjects were 37 randomly-selected untrained men. None of the exercises yielded significant correlations between fatness and RER. The results refute the initial hypothesis linking substrate oxidation and body fatness. Inspection of the body composition data for Wade's subjects reveals that they were abnormally lean. This suggests that their findings may have been confounded by coincident correlations between fitness and fatness, and may not represent a true causal relationship.

Absorptiometry, Photon↗
PubMed1994

Seasonal variations in vitamins A, C, riboflavin and folate intakes and status of pregnant and lactating women in a rural Gambian community: some possible implications.

OBJECTIVE: To relate measured intake of vitamins A, C, folate and riboflavin to biochemical indicators of nutritional status for these micronutrients, and to examine seasonal variations. SETTING: MRC Dunn Nutrition Unit Field Station, Keneba, The Gambia, which has heavy rainfall in August, and little or no rain between late September and mid-June. Data were collected during 1978-80. SUBJECTS: Pregnant or lactating women in a rural farming community whose diet has been studied throughout the year. RESULTS: Mean daily intake of vitamin C varied from virtually nil during the rainy season to about 100 mg/d in May, while plasma ascorbate ranged from 0.2 to 1.2 mg/dl, and breast-milk ascorbate from 2 to 6 mg/dl, changing synchronously with changing intake. Intake of retinol equivalents ranged from 120 micrograms/d in December to 900 micrograms/d in June, and plasma carotenoids showed synchronous fluctuation from 60 to 180 micrograms/dl, whereas plasma retinol was virtually unchanged throughout the year at 30 micrograms/dl. Intake of riboflavin was very low throughout the year, but erythrocyte glutathione reductase activation coefficient ranged from a minimum of 1.5 in July to a maximum of 1.9 between December and March. Obstetric outcome also exhibited seasonal variation with lowest birthweights during the rainy season. Intakes of food energy are assumed to be the major dietary influence on birthweight, but micronutrient intakes and status may have additional effects, and seasonality clearly affects ascorbate intakes by suckling infants. CONCLUSIONS: In countries such as The Gambia seasonality is a major determinant of micronutrient status. However, dietary intake is not the only factor which determines micronutrient status: thus there are seasonal fluctuations in riboflavin status which, for example, may relate to changes in the balance between energy intake and output, rather than to seasonal changes in riboflavin intake.

Adult↗
PubMed1993

Measurements of total energy expenditure provide insights into the validity of dietary measurements of energy intake.

The quantification of errors inherent in methods of measuring dietary intake has been handicapped by the absence of independent markers for testing their validity. The doubly labeled water technique permits a precise measure of energy expenditure in free-living persons. Because energy expenditure must equal energy intake in populations in energy balance, this technique may be used to validate the assessment of energy intake. A series of studies demonstrated good agreement between mean energy intake and mean energy expenditure when food intake was recorded by observers or when it was self-reported by normal-weight, self-selected, highly motivated volunteer subjects using weighed records. However, in randomly recruited men and women, energy intake by weighed records was 82% and 81%, of energy expenditure, respectively, indicating underestimation of habitual intake. Men and women in the lowest third of reported intake recorded energy expenditure of only 69% and 61%, respectively. Reported intake of obese and previously obese women was only 73% and 64% of expenditure, whether measured by weighed record or by diet history, confirming suspicions that these subjects misrepresented their intake. Acceptable weighed records were obtained from 7- and 9-year-olds whereas 15- and 18-year-olds underestimated intake. Diet histories taken from the same children tended to overestimate intake. These studies suggest that, ideally, all dietary studies should include independent measures of validity.

Adolescent↗