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Biomedical subjects

A M Prentice

Publications and source records attributed to A M Prentice.

At least 37 records · Page 2Linked to original sources
PubMed1999

Report of the IDECG Working Group on the modulating effect of stressors on the upper and lower limits of lipid and carbohydrate intake. International Dietary Energy Consultative Group.

The recommended caloric intake should be increased by 2870kJ (670Kcal)/d in the exclusively breast-feeding woman. Of this increase, 10% should be ingested as protein, up to 50% as lipid and no less than 40% as carbohydrate. If weight loss is desired lipid intake can be reduced but carbohydrate intake should be maintained. Of the total energy increment 3% should be supplied by essential fatty acids (linoleic and alpha-linolenic acids) and 0.5% by n-3 fatty acids. The issue of dietary supplementation with long-chain polyunsaturated fatty acids remains for future research.

Dietary Carbohydrates↗
PubMed1999

Effects of inactivity and diet composition on human energy balance.

OBJECTIVES: To investigate the influences of inactivity and dietary macronutrient composition on energy and fat balance and to look for interactions between them. DESIGN: Two-day measurements of energy expenditure and substrate oxidation on five occasions; ad libitum food intake from diets of 35% and 60% energy as fat, with and without imposed activity, and a fixed overfeeding at 35% fat with free activity. SUBJECTS: Eight normal-weight male volunteers. MEASUREMENTS: Energy expenditure and substrate oxidation by indirect whole-body calorimetry, and macronutrient intakes from food consumption on ad libitum regimens. RESULTS: Subjects consumed the same energy, mean 11.6 MJ/d, regardless of activity level, on the 35% diet. Subjects consumed more energy on the 60% than the 35% diet, mean 14 vs. 11.6 MJ/d. Inactivity induced a strong positive energy balance: 5.1 (60% diet), and 2.6 MJ/d (35% diet). Energy balance with activity was not significantly different between diets, nor significantly different from zero: 1.1 MJ/d (60% diet), and -0.2 MJ/d (35% diet). When intentionally overfed, subjects failed to compensate by raising voluntary activity. CONCLUSION: Energy intake was not regulated over a 2-day period in response to either imposition of inactivity or a high-fat diet. Activity proved essential to the avoidance of significant positive energy balance.

Adult↗
PubMed1999

Prenatal or early postnatal events predict infectious deaths in young adulthood in rural Africa.

BACKGROUND: Research over the past decade has suggested that prenatal and early postnatal nutrition influence the risk of developing chronic degenerative diseases up to 60 years later. We now present evidence that risk of death from infectious diseases in young adulthood is similarly programmed by early life events. METHODS: In three rural Gambian villages, affected by a marked annual seasonality in diet and disease, we have kept detailed demographic, anthropometric and health records since 1949. Fate was known with certainty for 3,162 individuals (2,059 alive/1,103 dead, most dying in childhood). For this case-control analysis of antecedent predictors of premature mortality, all adult deaths (n = 61) were paired with two randomly selected controls matched for sex and year of birth. RESULTS: Mean age at death was 25 (SD: 8) years. Adult death was associated with a profound bias in month of birth with 49 cases born in the nutritionally-debilitating hungry season (Jul-Dec) versus 12 in the harvest season (Jan-Jun). Relative to harvest season the hazard ratio for early death in hungry-season births rose from 3.7 (for deaths >14.5 years, P = 0.000013) to 10.3 (for deaths >25 years, P = 0.00002). Anthropometric and haematological status at 18 months of age was identical in cases and controls, indicating an earlier origin to the defect. Most deaths for which cause was known had a definite or possible infectious aetiology; none were from degenerative diseases of affluence. CONCLUSIONS: Early life exposures, correlated with season of birth, strongly influence susceptibility to fatal infections in young adulthood. The evidence suggests that nutritionally-mediated intrauterine growth retardation may permanently impair the development of immune function.

Adolescent↗
PubMed1998

A quantitative analysis of the relationship between habitual energy expenditure, fitness and the metabolic cardiovascular syndrome.

Previous epidemiological studies have suggested an association between low levels of physical activity, fitness and the metabolic cardiovascular syndrome. However, many studies have used subjective non-quantitative questionnaire-based methods for assessing physical activity which do not distinguish between the different dimensions of this complex exposure, and in which measurement error in the exposure has not been estimated. These deficiencies in the measurement of this exposure complicate the interpretation of the results of epidemiological studies, and consequently make it difficult to design appropriate interventions and to estimate the expected benefit which would result from intervention. In particular, it is unclear whether public health advice should be to increase total energy expenditure, or to attempt to raise fitness by recommending periods of vigorous activity. To separate the effects of fitness and total energy expenditure in the aetiology of the metabolic cardiovascular syndrome, we measured the physical activity level (PAL), defined as total energy expenditure: BMR, and fitness (maximum O2 consumption (VO2max per kg), measured in a sub-maximal test) in a cross-sectional population-based study of 162 adults aged 30-40 years. Heart-rate monitoring with individual calibration was used to measure total energy expenditure using the HRFlex method (Ceesay et al. 1989) which has been validated previously against doubly-labelled water and whole-body calorimetry. The relationship between a single measure of PAL, VO2max per kg and the usual or habitual level for each exposure was measured in a sub-study of twenty-two subjects who undertook four repeated measures over the course of 1 year. This study design allows the reliability coefficient to be computed, which is used to adjust the observed associations for measurement error in the exposure. Twelve men (16.4%) and sixteen women (18.0%) were defined as having one or more features of the metabolic cardiovascular syndrome. The univariate odds ratio for each increasing quartile for PAL was 0.64 (95% CI 0.43-0.94) and was 0.49 (95% CI 0.32-0.74) for VO2max per kg, suggesting that the association with the metabolic cardiovascular syndrome was stronger for fitness than for PAL. However, after adjustment for obesity and sex, and correction for exposure measurement error, the odds ratio per quartile for PAL was 0.32 (95% CI 0.13-0.83) and 0.44 (95% CI 0.24-0.78) for VO2max per kg. Thus, although univariate analysis would suggest that fitness has a stronger association with the metabolic cardiovascular syndrome than PAL, this conclusion is reversed once confounding and the differences in measurement error are considered. We conclude from the present study that the metabolic cardiovascular syndrome is strongly associated with reduced habitual energy expenditure. The method employed to assess the exposure in the present study demonstrates the utility of assessing a known dimension of physical activity using a physiologically-based and objective measure with repeated estimation to adjust for measurement error. Such quantitative epidemiological data provide the basis for planning and evaluating the expected benefit of population-level interventions.

Adult↗
PubMed1998

Assessment of selective under-reporting of food intake by both obese and non-obese women in a metabolic facility.

OBJECTIVE: To investigate the degree of bias in under-reporting of food intake in obese and non-obese subjects, hypothesising that under-reporting may be selective for either macronutrient content (carbohydrate (CHO), fat, protein, alcohol), specific food types or eating occasions (meals, snacks). DESIGN: Thirty-three women (18 obese, 15 non-obese) were recruited to a long-stay metabolic facility for 24h. Ad libitum food intake was covertly measured throughout the study and a reported food intake completed at the end of 24h. RESULTS: Reported total daily energy intake was significantly lower than measured intake. Whilst meals were accurately reported, energy from snack foods eaten between meals was significantly under-reported. (P< 0.001) Reported total carbohydrate and added sugar intakes were significantly lower than measured, whilst reported protein and fat intakes were not significantly different from measured. Reported alcohol intake was also considerably lower than measured, but high variability prevented significance. CONCLUSIONS: In both obese and non-obese women the major cause of under-reporting, as assessed by covert study design in subjects restricted within a metabolic facility, is the failure to report between-meal snack foods. There is some evidence for increased under-reporting in high CHO, but no evidence of a bias in under-reporting towards high fat or high protein foods.

Adult↗
PubMed1998

Leptin: physiology and pathophysiology.

The identification and sequencing of the ob gene and its product, leptin, in late 1994 opened new insights in the study of the mechanisms controlling body weight and led to a surge of research activity. During this time, a considerable body of knowledge regarding leptin's actions has been accumulated and the field continues to expand rapidly. Currently there is particular interest in the interaction of leptin with other peripheral and neural mechanisms to regulate body weight, reproduction and immunological response. In this review, we attempt to place the current state of knowledge about leptin in the broader perspective of physiology, including its structural characteristics, receptors, binding proteins, signalling pathways, regulation of adipose tissue expression and production, secretion patterns, clearance mechanisms and functional effects. In addition, leptin's involvement in the pathophysiology of obesity, anorexia nervosa, diabetes mellitus, polycystic ovary syndrome, acquired immunodeficiency syndrome, cancer, nephropathy, thyroid disease, Cushing's syndrome and growth hormone deficiency will be reviewed.

Animals↗
PubMed1998

Manipulation of dietary fat and energy density and subsequent effects on substrate flux and food intake.

Dietary fat has traditionally been viewed as being particularly lipogenic because of its high energy density, metabolic efficiency, and palatability. If these attributes of dietary fat were counteracted by a high satiating power, or if the body made autoregulatory adjustments in fat utilization in response to high fat intakes, energy balance would not necessarily be displaced. However, recent experiments have shown that neither of these hold true: human and animal trials consistently show that covert manipulation of dietary fat can induce hyperphagia, which can readily lead to spontaneous fat storage of 50-100 g/d in humans. Experiments with isoenergy-dense diets show that this high-fat hyperphagia (with diets of similar palatability) is caused by the high energy density of fatty foods rather than by their other attributes. Hyperphagia has therefore been termed passive overconsumption because it occurs unintentionally and without the consumption of excess bulk. When palatability is allowed to vary normally, high-fat foods may additionally induce active overconsumption in response to the enhanced organoleptic qualities of fats. In terms of substrate flux, fat is at the bottom of an oxidative hierarchy that determines fuel selection. Whereas alcohol, carbohydrates, and protein elicit powerful autoregulatory adjustments in their oxidation in response to changes in intake, fat fails to elicit such a response and fat balance is therefore easily displaced. These physiologic observations provide mechanistic support for secular-trend, cross-cultural, and cross-sectional epidemiologic studies investigating the role of energy-dense diets in the etiology of obesity.

Diet↗
PubMed1998

Effect of dietary manipulation on substrate flux and energy balance in obese women taking the appetite suppressant dexfenfluramine.

BACKGROUND: Studies in lean men show poor regulation of energy (EB) and fat balance (FB) during manipulation of dietary ratios of fat to carbohydrate. High-fat (HF), high-energy diets cause hyperphagia and a positive EB and FB. OBJECTIVE: The protocol was designed to measure substrate flux and EB in obese women taking dexfenfluramine (DF) or placebo (PL) during an HF (50% of energy) or low-fat (25% of energy; LF) diet. We hypothesized that alterations in dietary fat would not be regulated and would lead to a positive EB and FB. DESIGN: The study was double-blind, randomized, and placebo-controlled, with 4 treatments (LF/DF, HF/DF, LF/PL, and HF/PL) and a crossover. Five days of continuous, whole-body calorimetry measurements were made in 6 subjects after 8 d of home DF/PL treatment. Macronutrient balance and EB were measured within the chamber as the cumulative difference between ad libitum intake and oxidation. RESULTS: The HF diet increased energy (HF, 10.50 MJ/d; LF, 8.13 MJ/d; P < 0.0001) and fat intakes (HF, 5.34 MJ/d; LF, 2.06 MJ/d; P < 0.0001), leading to a positive EB (delta = 2.37 MJ/d) and FB (delta = 2.31 MJ/d). DF reduced energy (DF, 8.96 MJ/d; PL, 9.66 MJ/d; P < 0.01) and macronutrient intakes, but did not increase energy expenditure (delta = -0.31 MJ/d; P < 0.01), or 24-h fat oxidation (delta = 0.03 MJ/d; P = 0.46). CONCLUSIONS: EB and FB are poorly regulated with HF, energy-dense diets in obese women, which leads to fat deposition and weight gain.

Appetite Depressants↗
PubMed1998

Dietary compensation in response to covert imposition of negative energy balance by removal of fat or carbohydrate.

Compensatory changes in energy intake (EI) and macronutrient metabolism in response to modest covert underfeeding were tested by whole-body calorimetry in eight lean men. Each was studied on three occasions comprising a controlled stabilization day followed by manipulation and outcome days in a whole-body calorimeter. On the manipulation day EI was fixed, and calculated to maintain energy balance (CONTROL) or to provide 85% of CONTROL BY removing energy as carbohydrate (CHOred) or as fat (FATred). On the outcome day, ad libitum EI was allowed at fixed mealtimes. CHOred and FATred manipulations generated significantly different energy balances (-1.10 (SE 0.13) MJ, P = 0.000; -1.10 (SE 0.12) MJ, P = 0.000) and fat balances (-0.61 (SE 0.23) MJ, P = 0.03; -1.09 (SE 0.20) MJ, P = 0.000), but not carbohydrate balances (-0.39 (SE 0.22) MJ, NS; 0.11 (SE 0.23) MJ, NS) by the end of the manipulation day compared with CONTROL. On the outcome day, EI was significantly higher than CONTROL after CHOred (+1.58 (SE 0.33) MJ, P = 0.004) and FATred (+1.21 (SE 0.49) MJ, P = 0.022) with no differences between treatments. Overall 48 h energy balances averaged close to zero at -0.14, +0.34, +0.04 MJ on CONTROL, CHOred and FATred respectively. Total 48 h energy intakes on CHOred and FATred averaged 101 (SE 1.7)% and 99 (SE 2.5)% of CONTROL, thus demonstrating accurate detection of a mild energy deficit and efficient next-day compensation. Despite significant differences in macronutrient oxidation rates, the energy homeostatic mechanism appeared to be independent of specific macronutrient deficits.

Adult↗
PubMed1997

Effects on birth weight and perinatal mortality of maternal dietary supplements in rural Gambia: 5 year randomised controlled trial .

OBJECTIVE: To test the efficacy in terms of birth weight and infant survival of a diet supplement programme in pregnant African women through a primary healthcare system. DESIGN: 5 year controlled trial of all pregnant women in 28 villages randomised to daily supplementation with high energy groundnut biscuits (4.3 MJ/day) for about 20 weeks before delivery (intervention) or after delivery (control). SETTING: Rural Gambia. SUBJECTS: Chronically undernourished women (twin bearers excluded), yielding 2047 singleton live births and 35 stillbirths. MAIN OUTCOME MEASURES: Birth weight; prevalence of low birth weight (< 2500 g); head circumference; birth length; gestational age; prevalence of stillbirths; neonatal and postneonatal mortality. RESULTS: Supplementation increased weight gain in pregnancy and significantly increased birth weight, particularly during the nutritionally debilitating hungry season (June to October). Weight gain increased by 201 g (P < 0.001) in the hungry season, by 94 g (P < 0.01) in the harvest season (November to May), and by 136 g (P < 0.001) over the whole year. The odds ratio for low birthweight babies in supplemented women was 0.61 (95% confidence interval 0.47 to 0.79, P < 0.001). Head circumference was significantly increased (P < 0.01), but by only 3.1 mm. Birth length and duration of gestation were not affected. Supplementation significantly reduced perinatal mortality: the odds ratio was 0.47 (0.23 to 0.99, P < 0.05) for stillbirths and 0.54 (0.35 to 0.85, P < 0.01) for all deaths in first week of life. Mortality after 7 days was unaffected. CONCLUSION: Prenatal dietary supplementation reduced retardation in intrauterine growth when effectively targeted at genuinely at-risk mothers. This was associated with a substantial reduction in the prevalence of stillbirths and in early neonatal mortality. The intervention can be successfully delivered through a primary healthcare system.

Birth Weight↗
PubMed1997

Carbohydrates and energy balance.

In the early 1970s carbohydrates (CHOs) were believed to induce overconsumption and excess fat deposition. They are now perceived to protect against these consequences. This paper evaluates the evidence for this change of interpretation by considering (1) the energy content of CHOs, (2) the energetic efficiency with which they are handled by the body, and (3) their effects on appetite, relative to other macronutrients. CHOs are the least energy-dense macronutrients (delta Hc) and exhibit the greatest variability in digestibility. Doubling the usual levels of nonstarch polysaccharides (fiber) may decrease digestibility of a Western diet by 5%. De novo lipogenesis from dietary CHO is energetically inefficient but very limited on Western diets, which are relatively high in fat. There appears to be a hierarchy (protein > CHO > fat) in the extent to which the stores of the macronutrients are autoregulated by oxidation. Excess CHO intake tends to promote storage (but not de novo synthesis) of fat. The thermogenic effects of CHO are therefore relatively limited on Western diets. Per MJ of energy ingested, macronutrients differentially affect satiety (protein > CHO > fat) under conditions where fat is disproportionately energy dense. Isoenergetically dense loads of fat and CHO exert less pronounced differences on satiety. Under some conditions HC diets promote excess energy intakes. There is little evidence that a CHO-rich diet, or one with intense sweeteners, promotes spontaneous weight loss.

Dietary Carbohydrates↗
PubMed1997

Meal frequency and energy balance.

Several epidemiological studies have observed an inverse relationship between people's habitual frequency of eating and body weight, leading to the suggestion that a 'nibbling' meal pattern may help in the avoidance of obesity. A review of all pertinent studies shows that, although many fail to find any significant relationship, the relationship is consistently inverse in those that do observe a relationship. However, this finding is highly vulnerable to the probable confounding effects of post hoc changes in dietary patterns as a consequence of weight gain and to dietary under-reporting which undoubtedly invalidates some of the studies. We conclude that the epidemiological evidence is at best very weak, and almost certainly represents an artefact. A detailed review of the possible mechanistic explanations for a metabolic advantage of nibbling meal patterns failed to reveal significant benefits in respect of energy expenditure. Although some short-term studies suggest that the thermic effect of feeding is higher when an isoenergetic test load is divided into multiple small meals, other studies refute this, and most are neutral. More importantly, studies using whole-body calorimetry and doubly-labelled water to assess total 24 h energy expenditure find no difference between nibbling and gorging. Finally, with the exception of a single study, there is no evidence that weight loss on hypoenergetic regimens is altered by meal frequency. We conclude that any effects of meal pattern on the regulation of body weight are likely to be mediated through effects on the food intake side of the energy balance equation.

Adolescent↗
PubMed1997

Feasibility of heart-rate monitoring to estimate total level and pattern of energy expenditure in a population-based epidemiological study: the Ely Young Cohort Feasibility Study 1994-5.

Increasing the precision of measurements of total energy expenditure in population-based epidemiological studies is important for accurately quantifying the relationship between this exposure and disease. Current questionnaire-based methods cannot accurately quantify total energy expenditure, although they may provide an estimate of the frequency of vigorous activities. Heart rate monitoring with individual calibration has been advocated as a method for assessing energy expenditure in field studies and has been compared with the 'gold standard' techniques of doubly-labelled water and indirect calorimetry. However the method has previously only been used on small and selected populations. This study was, therefore, established to test the feasibility of using heart rate monitoring in a population-based study of adults. A total of 167 individuals aged 30-40 years were randomly selected and underwent 4 d heart-rate monitoring. Only three individuals could not complete the protocol. The mean physical activity level (PAL) measured over 4 d was 1.89 (SD 0.40) in men and 1.76 (sd 0.31) in women. There was no difference between mean PAL on weekend days compared with weekdays (mean paired difference 0.0008, 95% CI -0.06 +0.06). The estimate of mean PAL was not correlated with BMI, percentage body fat or the waist:hip ratio. It was, however, correlated with cardio-respiratory fitness as measured by VO2(max) per kg (Spearman rank correlation coefficient 0.50 in men and 0.42 in women). The pattern of energy expenditure was assessed by calculating the percentage of daytime hours in which PAL was greater than five times basal energy expenditure. This measure was strongly correlated with the mean PAL in both men (Spearman correlation coefficient 0.77) and women (0.71). We conclude that heart-rate monitoring is a feasible method for assessing the pattern and total level of energy expenditure in medium-sized epidemiological studies. It may also prove useful as the reference technique for calibrating questionnaires to estimate energy expenditure in larger scale studies.

Adult↗