Energy balance in human beings: the problems of plenitude

Factors determining insulin requirements in women with type 1 diabetes mellitus during pregnancy: a review

Most women with type 1 diabetes mellitus (T1DM) have increased insulin requirements during pregnancy. However, a minority of women have a fall in insulin requirements. When this occurs in late gestation, it often provokes concern regarding possible compromise of the feto-placental unit. In some centres, this is considered as an indication for delivery, including premature delivery. There are, however, many other factors that affect insulin requirements in pregnancy in women with type 1 diabetes mellitus and the decline in insulin requirements may represent a variant of normal pregnancy. If there is no underlying pathological process, expedited delivery in these women is not warranted and confers increased risks to the newborn. We will explore the factors affecting insulin requirements in gestation in this review. We will also discuss some novel concepts regarding beta-cell function in pregnancy.

The influence of the type of dietary fat on postprandial fat oxidation rates: monounsaturated (olive oil) vs saturated fat (cream)

OBJECTIVE

To compare postprandial whole-body fat oxidation rates in humans, following high-fat (43% of total energy) mixed breakfast meals, of fixed energy and macronutrient composition, rich in either monounsaturated fat (MUFA) from extra virgin olive oil or saturated fat (SFA) from cream.

DESIGN

Paired comparison of resting metabolic rate (RMR), thermic effect of a meal and substrate oxidation rates following consumption of isocaloric breakfast meals, differing only in the type of fat, administered in random order 1-2 weeks apart.

SUBJECTS

Fourteen male volunteers, body mass index (BMI) in the range 20-32 kg/m(2), aged 24-49 y and resident in Melbourne, Australia, were recruited by advertisement in the local media or by personal contact.

MEASUREMENTS

Body size and composition was determined by anthropometry and dual energy X-ray absorptiometry (DEXA). Indirect calorimetry was used to measure RMR, thermic effect of a meal, post-meal total energy expenditure and substrate oxidation rate. Blood pressure and pulse rates were measured with an automated oscillometric system. Fasting and 2 h postprandial glucose and insulin concentrations and the fasting lipid profile were also determined.

RESULTS

In the 5 h following the MUFA breakfast, there was a significantly greater postprandial fat oxidation rate (3.08+/-4.58 g/5 h, P=0.017), and lower postprandial carbohydrate oxidation rate (P=0.025), than after the SFA breakfast. Thermic effect of a meal was significantly higher (55 kJ/5 h, P=0.034) after the MUFA breakfast, in subjects with a high waist circumference (HWC > or = 99 cm) than those with a low waist circumference (LWC<99 cm). This difference was not detected following the SFA breakfast (P=0.910).

CONCLUSION

If postprandial fat oxidation rates are higher after high MUFA, rather than SFA meals, then a simple change to the type of dietary fat consumed might have beneficial effects in curbing weight gain in men consuming a relatively high-fat diet. This may be particularly evident in men with a large waist circumference.

Regional sympathetic nervous activity and oxygen consumption in obese normotensive human subjects

BACKGROUND

Disturbed sympathetic nervous function may be of importance in obesity; sympathetic underactivity could contribute to deficient thermogenesis, positive energy balance, and weight gain, while in contrast, sympathetic nervous overactivity would predispose to the development of obesity-related hypertension. Global indices of sympathetic nervous system (SNS) function such as plasma or urinary norepinephrine (NE) have been unable to define SNS status in obesity. Since regional SNS activity can be altered in the absence of global changes, we investigated SNS activity in the heart, kidneys, and hepatomesenteric bed in healthy human subjects across a wide body mass index (BMI) range of between 19.6 and 35.5.

METHODS AND RESULTS

Whole-body and regional plasma NE kinetics using [3H]-labeled NE were assessed. Regional oxygen consumption was measured by combining arteriovenous differences in oxygen content and regional blood flow. Arterial plasma NE and whole-body plasma NE spillover were unrelated to BMI. With a BMI cutoff of 27, mean cardiac NE spillover was 46% lower in the obese subjects when compared with the lean subjects (P=.017). Renal NE spillover was significantly correlated with BMI (r=.668, P=.001), the mean value in the obese subjects being more than twice that in the lean subjects. Hepatomesenteric NE spillover was comparable in lean and obese subjects. Renal and hepatomesenteric oxygen consumption were both significantly higher in the obese subjects compared with lean subjects.

CONCLUSIONS

Regional SNS activity is heterogeneous in the obese state. Important regional alterations, which may be clinically relevant, occur in the absence of changes in global indices of sympathetic nervous function. The enhanced renal NE spillover in obesity may have implications for the development of hypertension in this group, whereas the low cardiac sympathetic tone would be expected to be cardioprotective. Enhanced visceral oxygen consumption evident in the kidneys and hepatomesenteric circulation in proportion to body mass contributes to the greater resting oxygen consumption in obesity.

Postprandial thermogenesis at rest and postexercise before and after physical training in lean, obese, and mildly diabetic men

To determine the independent impact of physical training on postprandial thermogenesis at rest and after 1 hour of cycling at 100 W, 10 lean (15% +/- 1% body fat), 10 obese (33% +/- 2% fat), and six obese diet-controlled, type II diabetic men (34% +/- 4% fat) underwent 12 weeks of vigorous cycle ergometer training (4 h/wk at approximately 70% of maximum oxygen consumption [VO2max]) while maintaining body weight and composition. Body weight was held constant by refeeding the energy expended in each training session. Cardiorespiratory fitness increased by approximately 27%, but body weight and fat did not change. Before and at least 4 days after the last exercise session, energy expenditure was measured for 3 hours under four conditions: (1) rest, no meal; (2) rest, after a 720-kcal mixed meal; (3) postexercise after 1 hour cycling, no meal; and (4) postexercise, meal after exercise. The thermic effect of food was calculated as postprandial minus postabsorptive energy expenditure at rest and postexercise (kcal/3 h). Before and after training, the thermic effect of food during rest was lower in obese than in lean men, and lower in diabetic than in obese men (P less than .05). Thermogenesis was improved after short-term exercise in obese and diabetic men compared with that at rest, but was not normalized (P less than .05 for lean v obese, diabetic men). A significant effect of training on thermogenesis was due to a small but significant increase after training for diabetic men under the postexercise condition. Thus, while short-term exercise enhances but does not normalize thermogenesis in obese and diabetic men, long-term exercise training leading to increased cardiorespiratory fitness, in the absence of changes in body composition, leads to a small increase in thermogenesis in diabetic men, which manifests only after a short period of exercise.

Thermic effect of epinephrine: a role for endogenous insulin

The contribution of the basal insulin concentration to the metabolic response to epinephrine was measured in eight, postabsorptive, healthy volunteers before and during epinephrine (0.05 micrograms/kg fat-free mass [FFM] x min) and somatostatin (500 micrograms/h) infusion with and without insulin (0.1 mU/kg body weight [BW] x min) replacement. At basal plasma insulin concentrations, epinephrine increased oxygen consumption, heart rate, heart work, hepatic glucose production, glycogen breakdown in liver and muscle, and glucose oxidation, and the arterial plasma concentrations of glucose, lactate, and free fatty acids. Similar effects were observed during hypoinsulinemia, but epinephrine's actions on oxygen consumption and plasma concentrations of free fatty acids were disproportionally enhanced. We conclude that epinephrine-induced thermogenesis is partially inhibited by basal plasma insulin concentrations.

Thermic effect of a meal. 1. Methodology and variation in normal young adults

The variation in the thermic effect of a meal (TEM) was investigated in two groups of five subjects following a standard test meal. Results demonstrated a 50% lower response over 6 h, in the same subjects, when measured intermittently (protocol 2) as compared with a continuous measurement (protocol 1). The variation in TEM among occasions (measured on three occasions in each subject) was large (coefficient of variation (CV) 18.7%, P less than 0.02). However, the post-meal total energy output (CV 1.4%, P greater than 0.05), non-protein respiratory quotient (CV 1.9%, P greater than 0.05) and substrate oxidation rate were not different (P greater than 0.05) in the same individual on separate occasions. Small variations in the basal metabolic rate (BMR) from occasion to occasion (CV 2.6%) contributed to the variation in TEM. However, after allowing for the changes in BMR, variation in TEM (CV 8.6%, P greater than 0.05) was still sizeable though not statistically significant.

Thermogenic effect of adrenaline: interaction with insulin

The contribution of insulin (3.6 pmol.kg body mass-1.min-1) to adrenaline-induced (0.164 nmol.kg fat free mass-1.min-1) thermogenesis was studied in ten postabsorptive healthy volunteers using two sequential protocols. Variables considered were oxygen consumption as well as carbon dioxide production, heart rate, blood pressure, plasma concentrations of glucose, insulin, glycerol, free fatty acids, beta-HO-butyrate and lactate. Adrenaline increased plasma concentrations of glucose, glycerol, free fatty acids, and beta-HO-butyrate, and heart rate and metabolic rate during normo-insulinaemia [61.3 (SEM 6.6) pmol.l-1]. Similar effects were observed during hyperinsulinaemia [167.9 (SEM 18.7) pmol.l-1], but the effect of adrenaline on oxygen consumption was reduced. On average, metabolic rate increased by 12.9% during normo-insulinaemia and by 8.9% during hyperinsulinaemia. We concluded that relative hyperinsulinaemia resulted in decreased adrenaline-induced thermogenesis and therefore increased whole body anabolism.

The response to long-term overfeeding in identical twins

We undertook this study to determine whether there are differences in the responses of different persons to long-term overfeeding and to assess the possibility that genotypes are involved in such differences. After a two-week base-line period, 12 pairs of young adult male monozygotic twins were overfed by 4.2 MJ (1000 kcal) per day, 6 days a week, for a total of 84 days during a 100-day period. The total excess amount each man consumed was 353 MJ (84,000 kcal). During overfeeding, individual changes in body composition and topography of fat deposition varied considerably. The mean weight gain was 8.1 kg, but the range was 4.3 to 13.3 kg. The similarity within each pair in the response to overfeeding was significant (P less than 0.05) with respect to body weight, percentage of fat, fat mass, and estimated subcutaneous fat, with about three times more variance among pairs than within pairs (r approximately 0.5). After adjustment for the gains in fat mass, the within-pair similarity was particularly evident with respect to the changes in regional fat distribution and amount of abdominal visceral fat (P less than 0.01), with about six times as much variance among pairs as within pairs (r approximately 0.7). We conclude that the most likely explanation for the intrapair similarity in the adaptation to long-term overfeeding and for the variations in weight gain and fat distribution among the pairs of twins is that genetic factors are involved. These may govern the tendency to store energy as either fat or lean tissue and the various determinants of the resting expenditure of energy.

Strategies for analyzing nutritional data for epidemiological purposes--conceptual framework

The relation between nutritional factors and health investigated in epidemiological studies are often inconsistent. One of the reasons for such findings can be the improper addressing of the multitude of nutritional dimensions in the specific study situation such as physiological individuality of human beings, different living conditions, or numerous interdependencies between nutritional variables. Epidemiological research in nutrition and health should recognize such facts and work with appropriate study models and adequate data analyses. Instead of investigating heterogeneous populations it is advisable to concentrate on specific "types" of people. Under consideration of the study goals such "types" can be compiled according to physiological properties, e.g., cholesterol sensitivity, or biological-constitutional factors such as body build, life-style entities, or other factors. The variety of nutrition factors far beyond the commonly applied nutrient values can be expressed in integrated indices of "food patterns". Such "food patterns" can be derived in many ways. They can be deduced from theories by using specific criteria, but also explored by modern multivariate statistical analyses. The ways leading to "food patterns" are discussed. The ideas presented and discussed in this paper lead to an improved model for research in the field of nutrition and health with integrated indices of "food patterns" as the critical point. It is assumed that using this approach will generate new insight in the relation of nutrition and health, a currently still diffuse research area.

Thermogenesis in humans during overfeeding with medium-chain triglycerides

To test whether excess dietary energy as medium-chain triglycerides (MCT) affects thermogenesis differently from excess dietary energy as long chain triglycerides (LCT), ten male volunteers (ages 22 to 44) were overfed (150% of estimated energy requirement) liquid formula diets containing 40% of fat as either MCT or LCT. Each patient was studied for one week on each diet in a double-blind, crossover design. Resting metabolic rate (RMR) did not change during either week of overfeeding. The thermic response to food (TEF) was greater on day 1 following a meal (1,000 kcal) containing MCT than following an isocaloric meal containing LCT (8 +/- .8% v 5.8 +/- .8% of ingested energy; P less than .05). Moreover, the TEF observed after a 1,000 kcal meal containing MCT increased significantly to 12% (+/- 1.3%) overfeeding. The TEF of the 1,000 kcal meal containing LCT was unchanged by five days of LCT overfeeding (6.6 +/- 1.0% of ingested energy). Energy expenditure during a 20-hour continuous enteral infusion of the diet on day 7 was also significantly higher with the MCT diet than with the LCT diet (15.7 +/- 1.7% v 7.3 +/- .9% of ingested energy; P less than .05). Our results demonstrate that excess dietary energy as MCT stimulates thermogenesis to a greater degree than does excess energy as LCT. This increased energy expenditure, most likely due to lipogenesis in the liver, provides evidence that excess energy derived from MCT is stored with a lesser efficiency than is excess energy derived from dietary LCT.

The impact of food intake and exercise on energy expenditure

Food intake and physical exercise affect two components of energy expenditure, resting metabolic rate (RMR) and the thermic effect of feeding (TEF). Classic studies of overfeeding and underfeeding clearly showed that caloric deficit and surfeit conditions alter RMR. Recent work on short-term overfeeding of monozygotic twins provides new evidence that genetic factors influence individual sensitivity to changes in RMR and TEF when caloric excess is present. Exercise affects energy expenditure during nonactive times; acute bouts of vigorous exercise may result in increased RMR, and this effect appears most pronounced in the first 12 h after exercise. Acute exercise may potentiate the thermic effects of food when they are taken together, and high levels of exercise training may increase RMR. Thus, physical exercise appears to play an important role in the regulation of energy balance by way of its direct energy cost and its influence on RMR and TEF.

Experimental obesity: a homeostatic failure due to defective nutrient stimulation of the sympathetic nervous system

The basic hypothesis of this review is that studies on models of experimental obesity can provide insight into the control systems regulating body nutrient stores in humans. In this homeostatic or feedback approach to analysis of the nutrient control system, we have examined the afferent feedback signals, the central controller, and the efferent control elements regulating the controlled system of nutrient intake, storage, and oxidation. The mechanisms involved in the beginning and ending of single meals must clearly be related to the long-term changes in fat stores, although this relationship is far from clear. Changes in total nutrient storage in adipose tissue can arise as a consequence of changes in the quantity of nutrients ingested in one form or another or a decrease in the utilization of the ingested nutrients. A change in energy intake can be effected by increased size of individual meals, increased number of meals in a 24-hour period, or a combination of these events. Similarly, a decrease in utilization of these nutrients can develop through changes in resting metabolic energy expenditure which are associated with one of more of the biological cycles such as protein metabolism, triglyceride for glycogen synthesis and breakdown, or maintenance of ionic gradients for Na+ + K+ across cell walls. In addition, differences in energy expenditure related to the thermogenesis of eating or to the level of physical activity may account for differences in nutrient utilization.