Thermogenesis above maintenance in humans

The Metabolic Syndrome, a Human Disease

This review focuses on the question of metabolic syndrome (MS) being a complex, but essentially monophyletic, galaxy of associated diseases/disorders, or just a syndrome of related but rather independent pathologies. The human nature of MS (its exceptionality in Nature and its close interdependence with human action and evolution) is presented and discussed. The text also describes the close interdependence of its components, with special emphasis on the description of their interrelations (including their syndromic development and recruitment), as well as their consequences upon energy handling and partition. The main theories on MS's origin and development are presented in relation to hepatic steatosis, type 2 diabetes, and obesity, but encompass most of the MS components described so far. The differential effects of sex and its biological consequences are considered under the light of human social needs and evolution, which are also directly related to MS epidemiology, severity, and relations with senescence. The triggering and maintenance factors of MS are discussed, with especial emphasis on inflammation, a complex process affecting different levels of organization and which is a critical element for MS development. Inflammation is also related to the operation of connective tissue (including the adipose organ) and the widely studied and acknowledged influence of diet. The role of diet composition, including the transcendence of the anaplerotic maintenance of the Krebs cycle from dietary amino acid supply (and its timing), is developed in the context of testosterone and β-estradiol control of the insulin-glycaemia hepatic core system of carbohydrate-triacylglycerol energy handling. The high probability of MS acting as a unique complex biological control system (essentially monophyletic) is presented, together with additional perspectives/considerations on the treatment of this 'very' human disease.

The biology of human overfeeding: A systematic review

This systematic review has examined more than 300 original papers dealing with the biology of overfeeding. Studies have varied from 1 day to 6 months. Overfeeding produced weight gain in adolescents, adult men and women and in older men. In longer term studies, there was a clear and highly significant relationship between energy ingested and weight gain and fat storage with limited individual differences. There is some evidence for a contribution of a genetic component to this response variability. The response to overfeeding was affected by the baseline state of the groups being compared: those with insulin resistance versus insulin sensitivity; those prone to obesity versus those resistant to obesity; and those with metabolically abnormal obesity versus those with metabolically normal obesity. Dietary components, such as total fat, polyunsaturated fat and carbohydrate influenced the patterns of adipose tissue distribution as did the history of low or normal birth weight. Overfeeding affected the endocrine system with increased circulating concentrations of insulin and triiodothyronine frequently present. Growth hormone, in contrast, was rapidly suppressed. Changes in plasma lipids were influenced by diet, exercise and the magnitude of weight gain. Adipose tissue and skeletal muscle morphology and metabolism are substantially altered by chronic overfeeding.

Altered Brown Adipose Tissue and Na,K Pump Activities During Diet-Induced Obesity and Weight Loss in Rats

Brown adipose tissue (BAT) thermogenesis is an uncoupled ATPase-independent thermogenic mechanism. Ion transport by the Na,K pump is an ATPase-dependent thermogenic mechanism. Both have been proposed as mechanisms of altered energy expenditure during states of dietary energy surfeit and deficit. Our aim was to study these mechanisms during diet-induced obesity and weight loss. Over 36 weeks rats were fed lard- or tallow-based diets (63% energy as fat), or a control diet (12% energy as fat). During periods of restriction rats were fed 50% of the energy intake of controls in the form of a control diet. Several components of thermogenic response increased in rats eating high fat diets and decreased following dietary restriction. BAT activation occurred, particularly with a lard-based diet, as indicated by increased GDP binding and uncoupling protein (UCP) content. Na,K pump activity in thymocytes increased with the feeding of both high fat diets at some time points. Plasma T3 level increased in rats eating the lard-based diet and decreased with dietary restriction regardless of previous diet. Resting metabolic rate (RMR) of the animals was unchanged despite increases in these thermogenic components and was decreased in all groups following dietary restriction. Our results indicate a lack of any major role for activated BAT thermogenesis in mitigating the extent of the obesity induced by the high fat diets. The reasons for the differences in response to the two different sources of saturated fat, lard, and tallow, are not clear.

Different effects of hyperlipidic diets in human lactation and adulthood: growth versus the development of obesity

After birth, the body shifts from glucose as primary energy substrate to milk-derived fats, with sugars from lactose taking a secondary place. At weaning, glucose recovers its primogeniture and dietary fat role decreases. In spite of human temporary adaptation to a high-fat (and sugars and protein) diet during lactation, the ability to thrive on this type of diet is lost irreversibly after weaning. We could not revert too the lactating period metabolic setting because of different proportions of brain/muscle metabolism in the total energy budget, lower thermogenesis needs and capabilities, and absence of significant growth in adults. A key reason for change was the limited availability of foods with high energy content at weaning and during the whole adult life of our ancestors, which physiological adaptations remain practically unchanged in our present-day bodies. Humans have evolved to survive with relatively poor diets interspersed by bouts of scarcity and abundance. Today diets in many societies are largely made up from choice foods, responding to our deeply ingrained desire for fats, protein, sugars, salt etc. Consequently our diets are not well adjusted to our physiological needs/adaptations but mainly to our tastes (another adaptation to periodic scarcity), and thus are rich in energy roughly comparable to milk. However, most adult humans cannot process the food ingested in excess because our cortical-derived craving overrides the mechanisms controlling appetite. This is produced not because we lack the biochemical mechanisms to use this energy, but because we are unprepared for excess, and wholly adapted to survive scarcity. The thrifty mechanisms compound the effects of excess nutrients and damage the control of energy metabolism, developing a pathologic state. As a consequence, an overflow of energy is generated and the disease of plenty develops.

Metabolic efficiency and energy expenditure during short-term overfeeding

OBJECTIVE

To investigate whether efficiency of weight gain during a short period of overfeeding is related to adaptive differences in basal metabolic rate (BMR) and physical activity.

SUBJECTS

Fourteen healthy females (age 25+/-4 years, BMI 22.1+/-2.3 kg/m2).

DESIGN AND MEASUREMENTS

Subjects were overfed with a diet supplying 50% more energy than baseline energy requirements for 14 days. Overfeeding diets provided 7% of energy from protein, 40% from fat and 53% from carbohydrates. Body composition was determined using hydrodensitometry and isotope dilution, total energy expenditure (TEE) with doubly labeled water and basal metabolic rate (BMR) with indirect calorimetry. Physical activity (PA) was recorded with a tri-axial accelerometer.

RESULTS

Body weight increased by 1.45+/-0.86 kg (mean+/-S.D.) (P<0.0001), fat mass increased by 1.05+/-0.75 kg. Energy storage was 57.0+/-17.9 MJ, which is the difference between energy intake (207.2 MJ) and energy expenditure (150.2 MJ) during overfeeding. There was no difference between metabolically efficient and metabolically inefficient subjects in changes in BMR and PA.

CONCLUSION

These results indicate that the metabolic efficiency of weight gain was not related to adaptive changes in energy expenditure.

Growth and food intake responses to diets of different protein contents and a choice between diets containing two concentrations of protein in broiler and layer strains of chicken

1. Food intake, protein intake and body weight gain were measured in male broiler and layer strains of chickens offered approximately isocaloric diets containing various concentrations of protein from 4 to 9 weeks of age. The carcases were analysed for protein, fat and ash. 2. In the first experiment 5 birds of each strain were given diets containing either 65, 115, 172, 225 or 280 g protein/kg fresh matter. The sixth group was given a choice between 65 and 280 g/kg. There was an approximately linear increase in protein deposition with dietary protein content up to 280 g/kg with broilers and 225 g/kg with layers. When a choice of diets was offered, birds of both strains grew at a rate not significantly different from that of birds on the diets with the lowest protein content which gave maximal growth given singly, by making an apparently appropriate choice from the two diets. 3. In the second experiment broilers were offered a choice of two diets in the following combinations: 65 and 115, 65 and 225, 115 and 225, 225 and 280 and 280, and 320 g/kg protein. They were able to differentiate successfully between two diets on the basis of their protein content and, where the two diets were on either side of the optimum, to change the proportions selected as they grew to match their changing requirement for dietary protein. When given two diets, both of which had protein contents lower than the single diets which gave maximal growth, birds ate predominantly from that closer to that optimal diet. When both diets had a higher protein content than the optimum birds ate mostly from that closer to optimum. 4. The results show that growing chickens can match their protein intake closely to their requirements when given a pair of diets that allows this; if both diets are on the same side of the optimum then the one closest to that required is predominantly chosen.

[Energy balance in repeated under- and overnutrition in model studies in sows]

In a model experiment eight adult sows were used to examine the effect of successive periods of under- and oversupply of energy (MUMU) on thermogenesis and efficiency of energy utilization in comparison to a constant maintenance supply (NNNN). Each treatment sequence was assigned to each animal according to a change-over design over 8 weeks. Before and after the treatment periods all the animals were fed at maintenance level (N). Energy deficiency (M) was performed by use of a basal diet with 45% of maintenance energy requirements and values for all the other nutrients sufficient for requirements. Normal (N) and excessive (U) intakes of energy was provided with supplements of starch. The total inake of gross energy during the periods MUMU was exactly the same as during NNNN. Complete energy balances were performed for each animal and period as well as during the pre- and post-experimental phase. There was no or little response of altered energy intake on carbon and energy excretion in faeces, urine and methane. However, heat production was significantly decreased by 4.1% on energy deficiency, and increased by 15.1% during energy oversupply. Summed up over the total sequence the animals produced 5.4% more heat on MUMU than during NNNN. This response was associated with a mobilization of 1.1 MJ/d tissue energy and a decrease in body weight by 2.0 kg. The efficiency of utilization of ME was 88% with energy undersupply and 75% during overnutrition. Criteria of energy balance did not differ between the pre- and post-treatment periods. It could be demonstrated that the increase in energy expenditure at oversupply was entirely explainable by the so-called obligatory thermogenesis. At the energy deficiency periods the efficiency of energy utilization reflected both energy costs of ingestion and processing of nutrients as well as a slight reduction in metabolic rate. Finally, there were no residual effects of the treatment on the energy expenditure of the animals at the end of the experiment.

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.