Metabolic adaptation to weight loss: implications for the athlete . The metabolic effects of this process have been given little context within athletics, such as physique sports (i. Previous literature has documented cases of male bodybuilders reducing body fat to less than 5% of total body mass . A study on elite female gymnasts and runners reported an average body fat percentage (BF%) of 1. Elite female runners have also reported percent body fat levels below 1. Energy deficits and extremely low levels of body fat present the body with a significant physiological challenge. It has been well documented that weight loss and energy restriction result in a number of homeostatic metabolic adaptations aimed at decreasing energy expenditure, improving metabolic efficiency, and increasing cues for energy intake . While the unfavorable endocrine effects of contest preparation have been documented in male bodybuilders . Although such reports could potentially be related to inaccurate dietary reporting . As a dieting phase progresses, such adaptations may threaten dietary adherence, make further weight loss increasingly difficult, and predispose the individual to rapid weight regain following the cessation of the diet. Although data documenting the attainment and recovery from extreme changes in body composition is limited, the present article aims to investigate the condition of metabolic adaptation described by competitors and identify potential mechanisms to explain such a phenomenon. The endocrine response to an energy deficit. A number of hormones play prominent roles in the regulation of body composition, energy intake, and energy expenditure. The hormones of the thyroid gland, particularly triiodothyronine (T3), are known to play an important and direct role in regulating metabolic rate. While acidophiles, alkaliphiles, and piezophiles are their own class of Archaea, their protein adaptations toward pH and pressure are less discernible.Genetic variations in the Inuit of Greenland may reflect adaptations to the specific diet and climate their ancestors have experienced for thousands of years. The adaptations to varying protein intakes are examined below. For example, in one study rats were given an essentially protein-free diet. Increases in circulating thyroid hormones are associated with an increase in the metabolic rate, whereas lowered thyroid levels result in decreased thermogenesis and overall metabolic rate . Leptin, synthesized primarily in adipocytes, functions as an indicator of both short and long- term energy availability; short- term energy restriction and lower body fat levels are associated with decreases in circulating leptin. ![]() ![]() Definition of low-carbohydrate diet. Much of the controversy in the study of LCDs stems from a lack of a clear definition. The rationale of carbohydrate restriction. A healthy diet may help to prevent certain chronic (long-term) diseases such as heart disease, stroke and diabetes. Healthy eating diet plan at patient.info. Additionally, higher concentrations of leptin are associated with increased satiety and energy expenditure . Insulin, which plays a crucial role in inhibiting muscle protein breakdown . Learn everything you need to know about protein in the protein bible! Will a high protein diet. Five days of a high-fat diet produce metabolic adaptations that. We determined the effect of fat adaptation on metabolism. A healthy eating plan is key to a balanced diet and maintaining nutrition, fitness and a healthy weight. Similar to leptin, high levels of insulin convey a message of energy availability and are associated with an anorexigenic effect. Conversely, the orexigenic hormone ghrelin functions to stimulate appetite and food intake, and has been shown to increase with fasting, and decrease after feeding . Testosterone, known primarily for its role in increasing muscle protein synthesis and muscle mass . Changes in fat mass have been inversely correlated with testosterone levels, and it has been suggested that testosterone may repress adipogenesis . More research is needed to delineate the exact mechanism (s) by which testosterone affects adiposity. Cortisol, a glucocorticoid that influences macronutrient metabolism, has been shown to induce muscle protein breakdown . Evidence also suggests that glucocorticoids may inhibit the action of leptin . Studies involving energy restriction, or very low adiposity, report decreases in leptin . Subsequently, increases in ghrelin . Further, there is evidence to suggest that unfavorable changes in circulating hormone levels persist as subjects attempt to maintain a reduced body weight, even after the cessation of active weight loss . It should be noted that despite alterations in plasma levels of anabolic and catabolic hormones, losses of lean body mass (LBM) often fail to reach statistical significance in studies on bodybuilding preparation . Although the lack of significance may relate to insufficient statistical power, these findings may indicate that unfavorable, hormone- mediated changes in LBM can potentially be attenuated by sound training and nutritional practices. Previous research has indicated that structured resistance training . Further, Maestu et al. The hormonal environment created by low adiposity and energy restriction appears to promote weight regain and threaten lean mass retention, but more research is needed to determine the chronic impact of these observed alterations in circulating anabolic and catabolic hormones. Weight loss and metabolic rate. An individual. The largest component, resting energy expenditure (REE), refers to the basal metabolic rate (BMR) . The other component, known as non- resting energy expenditure (NREE), can be further divided into exercise activity thermogenesis (EAT), non- exercise activity thermogenesis (NEAT), and the thermic effect of food (TEF) . Adapted from Maclean et al., 2. Metabolic rate is dynamic in nature, and previous literature has shown that energy restriction and weight loss affect numerous components of energy expenditure. In weight loss, TDEE has been consistently shown to decrease . Weight loss results in a loss of metabolically active tissue, and therefore decreases BMR . Interestingly, the decline in TDEE often exceeds the magnitude predicted by the loss of body mass. Previous literature refers to this excessive drop in TDEE as adaptive thermogenesis, and suggests that it functions to promote the restoration of baseline body weight . Adaptive thermogenesis may help to partially explain the increasing difficulty experienced when weight loss plateaus despite low caloric intake, and the common propensity to regain weight after weight loss. Exercise activity thermogenesis also drops in response to weight loss . In activity that involves locomotion, it is clear that reduced body mass will reduce the energy needed to complete a given amount of activity. Interestingly, when external weight is added to match the subject. It has been speculated that this increase in skeletal muscle efficiency may be related to the persistent hypothyroidism and hypoleptinemia that accompany weight loss, resulting in a lower respiratory quotient and greater reliance on lipid metabolism . Roughly 1. 0% of TDEE is attributed to TEF . While the relative magnitude of TEF does not appear to change with energy restriction . NEAT, or energy expended during . There is evidence to suggest that spontaneous physical activity, a component of NEAT, is decreased in energy restricted subjects, and may remain suppressed for some time after subjects return to ad libitum feeding . Persistent suppression of NEAT may contribute to weight regain in the post- diet period. In order to manipulate an individual. In the context of weight loss or maintaining a reduced body weight, this process is complicated by the dynamic nature of energy expenditure. In response to weight loss, reductions in TDEE, BMR, EAT, NEAT, and TEF are observed. Due to adaptive thermogenesis, TDEE is lowered to an extent that exceeds the magnitude predicted by losses in body mass. Further, research indicates that adaptive thermogenesis and decreased energy expenditure persist after the active weight loss period, even in subjects who have maintained a reduced body weight for over a year . These changes serve to minimize the energy deficit, attenuate further loss of body mass, and promote weight regain in weight- reduced subjects. Adaptations in mitochondrial efficiency. A series of chemical reactions must take place to derive ATP from stored and ingested energy substrates. In aerobic metabolism, this process involves the movement of protons across the inner mitochondrial membrane. When protons are transported by ATP synthase, ATP is produced. Protons may also leak across the inner membrane by way of uncoupling proteins (UCPs) . Proton leak is a significant contributor to energy expenditure, accounting for roughly 2. BMR in rats . Uncoupling protein- 1 and UCP- 3, the primary UCPs of brown adipose tissue (BAT) and skeletal muscle . Decreased UCP- 3 expression could potentially play a role in decreasing energy expenditure, and UCP- 3 expression has been negatively correlated with body mass index and positively correlated with metabolic rate during sleep . Despite these correlations, more research is needed to determine the function and physiological relevance of UCP- 3 . Energy restriction has been shown to decrease BAT activation . Along with UCP- 1 expression, thyroid hormone and leptin affect the magnitude of uncoupled respiration in BAT. Thyroid hormone (TH) and leptin are associated with increased BAT activation, whereas glucocorticoids oppose the BAT- activating function of leptin . Evidence indicates that TH plays a prominent role in modulating the magnitude of proton leak . The endocrine response to energy restriction, including increased cortisol and decreased TH and leptin . It is not clear if decreases in proton leak and UCP expression persist until weight reverts to baseline, but there is evidence to suggest a persistent adaptation . In the context of energy restriction, the observed changes are likely to make weight loss increasingly challenging and promote weight regain. It has been reported that females have more BAT than males . Subjects identified as . More research is needed to determine if these differential responses to hypocaloric diets make sustained weight loss more difficult for females and certain predisposed . While future research may improve our understanding of the magnitude and relative importance of mitochondrial adaptations to energy restriction, current evidence suggests that increased mitochondrial efficiency, and a decline in uncoupled respiration, might serve to decrease the energy deficit in hypocaloric conditions, making weight maintenance and further weight reduction more challenging. Practical applications for weight loss in athletes. Hypocaloric diets induce a number of adaptations that serve to prevent further weight loss and conserve energy.
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