Starvation as a Treatment of Obesity: The Need to Conserve Body Protein

Maho, Yvon Le; Jp, Robin; Cherel, Yves

doi:10.1152/physiologyonline.1988.3.1.21

Cited by 25 publications

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“…It was found that the experimental values of this ratio varied only slightly during phase II (26,33). The data in Fig.…”

Section: Protein Sparing In Relation To Initial Adipositymentioning

confidence: 85%

“…It must be noted that this last phase is not systematically observed (22,41). It seems to have never been observed in obese subjects (33).…”

mentioning

confidence: 94%

“…By contrast, proteins, which have a much lower energy density, can be only partly depleted due to their vital enzymatic, mechanical, and structural roles. Accordingly, their contribution to energy demand is rather modest (17,28,33,37). The result is that, conversely to lipid catabolism, protein catabolism is not clearly related to energy production and remains essentially unexplained (27).…”

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confidence: 99%

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Modeling of lipid and protein depletion during total starvation

Caloin¹

2004

American Journal of Physiology-Endocrinology and Metabolism

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Caloin, Michel. Modeling of lipid and protein depletion during total starvation. Am J Physiol Endocrinol Metab 287: E790 -E798, 2004. First published May 27, 2004 10.1152/ajpendo.00414.2003This study presents a model describing lipid and protein depletion of an individual facing total starvation. The model distinguishes two compartments of body mass: a metabolic compartment and a structural compartment. It is considered that the lipids and the proteins of the metabolic compartment ensure the totality of physiological functions. The main assumptions of the model lie in the definitions of lipid mass and protein mass of the metabolic compartment, which are related to total lipid mass and total body mass, respectively. Under these assumptions, for a given individual, the ratio of lipid and protein utilization rates is proportional to the adiposity. The model accounts for the protein sparing observed at high adiposity levels and enables us to discuss the individual's survival in relation to the levels of lipid and protein depletion. The time course of changes in lipid and protein depletion rates can be calculated by introducing the energy expenditure of the individual. In simulations, it was assumed that specific energy expenditure was constant during starvation and that mortality occurred at a critical level of protein depletion. The most characteristic results derived from these simulations concern the kinetics of protein depletion, which depend markedly on initial adiposity. Accordingly, in obese subjects, the rate of protein losses remains fairly constant during fasting, whereas it increases from the onset of the fast in lean subjects, in agreement with experimental observations. In the model, protein and lipid depletion rates are both proportional to energy expenditure, which needs to be confirmed from complementary data. body composition; protein sparing; energy expenditure DURING TOTAL STARVATION, the energy required to maintain physiological functions is derived from the oxidation of body lipids and proteins, because glycogen stores are exhausted at the onset of fasting (3). Lipids, however, represent the main energy source. They have a high energy density and can be almost entirely depleted to cover maintenance requirements (45,49). By contrast, proteins, which have a much lower energy density, can be only partly depleted due to their vital enzymatic, mechanical, and structural roles. Accordingly, their contribution to energy demand is rather modest (17,28,33,37). The result is that, conversely to lipid catabolism, protein catabolism is not clearly related to energy production and remains essentially unexplained (27). It could be attributed to gluconeogenesis, which converts proteins into glucose to meet the glucose requirements of the brain after the exhaustion of glycogen stores (2, 4). However, this hypothesis is unlikely, given the large variability in the rate of protein depletion among individuals (14,16,36). To better understand the physiological basis for protein catabolism and its consequences for ...

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“…It was found that the experimental values of this ratio varied only slightly during phase II (26,33). The data in Fig.…”

Section: Protein Sparing In Relation To Initial Adipositymentioning

confidence: 85%

“…It must be noted that this last phase is not systematically observed (22,41). It seems to have never been observed in obese subjects (33).…”

mentioning

confidence: 94%

mentioning

confidence: 99%

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Modeling of lipid and protein depletion during total starvation

Caloin¹

2004

American Journal of Physiology-Endocrinology and Metabolism

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“…The mass specific rate of change in body mass (dM b /M b ⅐dt) remained more or less constant beyond day 5 of the fasting period (14.4 Ϯ 2.4 g⅐kg Ϫ1 ⅐day Ϫ1 ), and no bird showed an increase in dM b /M b ⅐dt before their release. This indicated that no animal entered phase III of fasting (25,32), which is associated with a signal to abandon the egg and refeed in the free-ranging bird.…”

Section: Body Mass During Fastingmentioning

confidence: 99%

Metabolism and thermoregulation during fasting in king penguins,Aptenodytes patagonicus,in air and water

Fahlman

Schmidt²,

Handrich³

et al. 2005

American Journal of Physiology-Regulatory, Integrative and Comp

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We measured oxygen consumption rate (V O2) and body temperatures in 10 king penguins in air and water. V O2 was measured during rest and at submaximal and maximal exercise before (fed) and after (fasted) an average fasting duration of 14.4 Ϯ 2.3 days (mean Ϯ 1 SD, range 10 -19 days) in air and water. Concurrently, we measured subcutaneous temperature and temperature of the upper (heart and liver), middle (stomach) and lower (intestine) abdomen. The mean body mass (M b) was 13.8 Ϯ 1.2 kg in fed and 11.0 Ϯ 0.6 kg in fasted birds. After fasting, resting V O2 was 93% higher in water than in air (air: 86.9 Ϯ 8.8 ml/min; water: 167.3 Ϯ 36.7 ml/min, P Ͻ 0.01), while there was no difference in resting V O2 between air and water in fed animals (air: 117.1 Ϯ 20.0 ml O 2/min; water: 114.8 Ϯ 32.7 ml O2/min, P Ͼ 0.6). In air, V O2 decreased with Mb, while it increased with Mb in water. Body temperature did not change with fasting in air, whereas in water, there were complex changes in the peripheral body temperatures. These latter changes may, therefore, be indicative of a loss in body insulation and of variations in peripheral perfusion. Four animals were given a single meal after fasting and the temperature changes were partly reversed 24 h after refeeding in all body regions except the subcutaneous, indicating a rapid reversal to a prefasting state where body heat loss is minimal. The data emphasize the importance in considering nutritional status when studying king penguins and that the fasting-related physiological changes diverge in air and water. thermoregulatory plasticity; hypometabolism; sea bird; allometry THE USE OF HEART RATE (f H ) as an indicator of the oxygen consumption rate (V O 2 ) has previously been used to estimate field metabolic rate in king penguins both on land and in water (21). Unfortunately, the relationship between f H and V O 2 for a given species does not necessarily remain constant throughout the life history. The relationship has been shown to vary with the type of activity (7, 43), physiological state (fasting, breeding; 17, 20), and with season (28). Whereas the relationship was shown to be similar in air and water in gentoo (3) and macaroni penguins (24), the use of f H to predict V O 2 in other penguin species requires validation studies to be performed both in water and on land.Before attempting to estimate the relationship between f H and V O 2 in king penguins in water, we considered it crucial first to study the complex body temperature changes (thermoregulatory plasticity) reported in this species (26). This is important for two reasons. First, we previously measured a significant reduction in V O 2 during fasting in air and hypothesized that this was in part due to a change in the body temperature of the birds (17). This observation prompted us to try to determine whether similar changes occur in king penguins while fasting in water. Secondly, as V O 2 decreases during fasting in air, a rapid reversal of this reduction after refeeding would be indicative of physiological or biochem...

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“…Then a metabolic shift occurs, and animals enter a new fasting state (phase III) corresponding to a simultaneous acceleration in the catabolism of protein and a decrease in the contribution of lipid to energy production (21,46). This shift has been described in experimentally fasted laboratory mammals (21,34) and in birds that spontaneously fast for prolonged periods at certain stages of their annual cycle, such as penguins (23,37). Nevertheless, the way the metabolic shift is triggered and how the utilization of the metabolic fuels is regulated during phase II and phase III are poorly understood.…”

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confidence: 99%

Lipolytic and metabolic response to glucagon in fasting king penguins: phase II vs. phase III

Bernard¹,

Thil²,

Groscolas³

2003

American Journal of Physiology-Regulatory, Integrative and Comp

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This study aims to determine how glucagon intervenes in the regulation of fuel metabolism, especially lipolysis, at two stages of a spontaneous long-term fast characterized by marked differences in lipid and protein availability and/or utilization (phases II and III). Changes in the plasma concentration of various metabolites and hormones, and in lipolytic fluxes as determined by continuous infusion of [2-3 H]-glycerol and [1-14 C]palmitate, were examined in vivo in a subantarctic bird (king penguin) before, during, and after a 2-h glucagon infusion. In the two fasting phases, glucagon infusion at a rate of 0.025 g ⅐ kg Ϫ1 ⅐ min Ϫ1 induced a three-to fourfold increase in the plasma concentration and in the rate of appearance (R a) of glycerol and nonesterified fatty acids, the percentage of primary reesterification remaining unchanged. Infusion of glucagon also resulted in a progressive elevation of the plasma concentration of glucose and ␤-hydroxybutyrate and in a twofold higher insulinemia. These changes were not significantly different between the two phases. The plasma concentrations of triacylglycerols and uric acid were unaffected by glucagon infusion, except for a 40% increase in plasma uric acid in phase II birds. Altogether, these results indicate that glucagon in a long-term fasting bird is highly lipolytic, hyperglycemic, ketogenic, and insulinogenic, these effects, however, being similar in phases II and III. The maintenance of the sensitivity of adipose tissue lipolysis to glucagon could suggest that the major role of the increase in basal glucagonemia observed in phase III is to stimulate gluconeogenesis rather than fatty acid delivery. lipolysis; ketone bodies; glucose; isotopic tracers; seabirds MAMMALS AND BIRDS adjust to long-term fasting by mobilizing their fat stores and sparing body proteins (8,14,21). However, the conservation of body protein that characterizes the so-called phase II of fasting is no longer maintained when a lower threshold of fat stores is reached. Then a metabolic shift occurs, and animals enter a new fasting state (phase III) corresponding to a simultaneous acceleration in the catabolism of protein and a decrease in the contribution of lipid to energy production (21, 46). This shift has been described in experimentally fasted laboratory mammals (21, 34) and in birds that spontaneously fast for prolonged periods at certain stages of their annual cycle, such as penguins (23, 37). Nevertheless, the way the metabolic shift is triggered and how the utilization of the metabolic fuels is regulated during phase II and phase III are poorly understood.Among the various hormones that could intervene to regulate fuel utilization, glucagon is likely to play a major role. Although the evidence for a lipolytic action in humans is scarce (10), glucagon stimulates lipolysis in vitro in mammals (38,52) and is the main lipolytic hormone in birds (9,22,36). It therefore plays a key role in the mobilization of fatty acids (FA) from adipose tissue. In mammals, glucagon also appears to influen...

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Starvation as a Treatment of Obesity: The Need to Conserve Body Protein

Cited by 25 publications

References 0 publications

Modeling of lipid and protein depletion during total starvation

Modeling of lipid and protein depletion during total starvation

Metabolism and thermoregulation during fasting in king penguins,Aptenodytes patagonicus,in air and water

Lipolytic and metabolic response to glucagon in fasting king penguins: phase II vs. phase III

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