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it appears that protein synthesis rapidly increases for up to two hours after amino acid administration

The intervention of dietary protein or amino acid supplementation in conjunction with resistance training has proven to effectively increase protein synthesis rates

291% increase in protein synthesis following the exercise bout, while protein degradation remained unchanged from baseline quantities

it has been established that post-exercise EAA supplementation stimulates protein synthesis, in conjunction with a positive protein balance, comparable to that of intravenous infusion of amino acids

Casein and whey protein ingestion yielded similar values of net positive protein balance, and thus an overall increase in protein synthesis

A later analysis revealed that soy protein increased protein synthesis in rats similar to that of whey after a treadmill exercise protocol

A human trial, however, concluded that milk proteins (caseins and whey) in comparison to soy promoted greater muscle protein accretion when they were ingested after regular resistance training

Whey hydrolysate ingested after a resistance exercise bout acutely stimulated mixed muscle protein synthesis 31% greater than soy

adequate amount of protein (20 g) is ingested (Tipton et al., 2009) immediately before or after a resistance exercise bout

The rapid phase lasts approximately 30-60 minutes and does not require the presence of insulin

slow phase, which can last up to several hours if carbohydrate availability is high and insulin levels remain elevated

there is evidence from animal studies that leptin resistance, inflammation and oestrogens inhibit neuronal release of kisspeptin

Beyond hypothalamic action, leptin also directly inhibits the stimulatory action of gonadotrophins on the Leydig cells of the testis to decrease testosterone production; therefore, elevated leptin levels in obesity may further diminish androgen status

Prostate cancer patients with pre-existing T2DM show a further deterioration of insulin resistance and worsening of diabetic control following ADT

ADT for the treatment of prostatic carcinoma in some large epidemiological studies has been shown to be associated with an increased risk of developing MetS and T2DM

Non-diabetic men undergoing androgen ablation show increased occurrence of new-onset diabetes and demonstrate elevated insulin levels and worsening glycaemic control

increasing insulin resistance assessed by glucose tolerence test and hypoglycemic clamp was shown to be associated with a decrease in Leydig cell testosterone secretion in men

The response to testosterone replacement of insulin sensitivity is in part dependent on the androgen receptor (AR)

Low levels of testosterone have been associated with an atherogenic lipoprotein profile, characterised by high LDL and triglyceride levels

a positive correlation between serum testosterone and HDL has been reported in both healthy and diabetic men

up to 70% of the body's insulin sensitivity is accounted for by muscle

Testosterone deficiency is associated with a decrease in lean body mass

relative muscle mass is inversely associated with insulin resistance and pre-diabetes

GLUT4 and IRS1 were up-regulated in cultured adipocytes and skeletal muscle cells following testosterone treatment at low dose and short-time incubations

local conversion of testosterone to DHT and activation of AR may be important for glucose uptake

inverse correlation between testosterone levels and adverse mitochondrial function

orchidectomy of male Wistar rats and associated testosterone deficiency induced increased absorption of glucose from the intestine

(Kelley & Mandarino 2000). Frederiksen et al. (2012a) recently demonstrated that testosterone may influence components of metabolic flexibility as 6 months of transdermal testosterone treatment in aging men with low–normal bioavailable testosterone levels increased lipid oxidation and decreased glucose oxidation during the fasting state.

Decreased lipid oxidation coupled with diet-induced chronic FA elevation is linked to increased accumulation of myocellular lipid, in particular diacylglycerol and/or ceramide in myocytes

In the Chang human adult liver cell line, insulin receptor mRNA expression was significantly increased following exposure to testosterone

Testosterone deprivation via castration of male rats led to decreased expression of Glut4 in liver tissue, as well as adipose and muscle

oestrogen was found to increase the expression of insulin receptors in insulin-resistant HepG2 human liver cell line

FFA decrease hepatic insulin binding and extraction, increase hepatic gluconeogenesis and increase hepatic insulin resistance.

Only one, albeit large-scale, population-based cross-sectional study reports an association between low serum testosterone concentrations and hepatic steatosis in men (Völzke et al. 2010)

This suggests that testosterone may confer some of its beneficial effects on hepatic lipid metabolism via conversion to E2 and subsequent activation of ERα.

hypogonadal men exhibiting a reduced lean body mass and an increased fat mass, abdominal or central obesity

visceral adipose tissue was inversely correlated with bioavailable testosterone

there was no change in visceral fat mass in aged men with low testosterone levels following 6 months of transdermal TRT, yet subcutaneous fat mass was significantly reduced in both the thigh and the abdominal areas when analysed by MRI (Frederiksen et al. 2012b)

ADT of prostate cancer patients increased both visceral and subcutaneous abdominal fat in a 12-month prospective observational study (Hamilton et al. 2011)

Catecholamines are the major lipolysis regulating hormones in man and regulate adipocyte lipolysis through activation of adenylate cyclase to produce cAMP

deficiency of androgen action decreases lipolysis and is primarily responsible for the induction of obesity (Yanase et al. 2008)

may be some regional differences in the action of testosterone on subcutaneous and visceral adipose function

proinflammatory adipocytokines IL1, IL6 and TNFα are increased in obesity with a downstream effect that stimulates liver production of CRP

observational evidence suggests that IL1β, IL6, TNFα and CRP are inversely associated with serum testosterone levels in patients

TRT has been reported to significantly reduce these proinflammatory mediators

This suggests a role for AR in the metabolic actions of testosterone on fat accumulation and adipose tissue inflammatory response

testosterone treatment may have beneficial effects on preventing the pathogenesis of obesity by inhibiting adipogenesis, decreasing triglyceride uptake and storage, increasing lipolysis, influencing lipoprotein content and function and may directly reduce fat mass and increase muscle mass

Early interventional studies suggest that TRT in hypogonadal men with T2DM and/or MetS has beneficial effects on lipids, adiposity and parameters of insulin sensitivity and glucose control

Evidence that whole-body insulin sensitivity is reduced in testosterone deficiency and increases with testosterone replacement supports a key role of this hormone in glucose and lipid metabolism

Impaired insulin sensitivity in these three tissues is characterised by defects in insulin-stimulated glucose transport activity, in particular into skeletal muscle, impaired insulin-mediated inhibition of hepatic glucose production and stimulation of glycogen synthesis in liver, and a reduced ability of insulin to inhibit lipolysis in adipose tissue

Thus, while glucose metabolism is negatively regulated by phosphofructokinase, fructose can continuously enter the glycolytic pathway. Therefore, fructose can uncontrollably produce glucose, glycogen, lactate, and pyruvate, providing both the glycerol and acyl portions of acyl-glycerol molecules. These particular substrates, and the resultant excess energy flux due to unregulated fructose metabolism, will promote the over-production of TG (reviewed in [53]).

Glycemic excursions and insulin responses were reduced by 66% and 65%, respectively, in the fructose-consuming subjects

reduction in circulating leptin both in the short and long-term as well as a 30% reduction in ghrelin (an orexigenic gastroenteric hormone) in the fructose group compared to the glucose group.

A prolonged elevation of TG was also seen in the high fructose subjects

Both fat and fructose consumption usually results in low leptin concentrations which, in turn, leads to overeating in populations consuming energy from these particular macronutrients

Chronic fructose consumption reduces adiponectin responses, contributing to insulin resistance

A definite relationship has also been found between metabolic syndrome and hyperhomocysteinemia

the liver takes up dietary fructose rapidly where it can be converted to glycerol-3-phosphate. This substrate favours esterification of unbound FFA to form the TG

Fructose stimulates TG production, but impairs removal, creating the known dyslipidemic profile

the effects of fructose in promoting TG synthesis are independent of insulinemia

Although fructose does not appear to acutely increase insulin levels, chronic exposure seems to indirectly cause hyperinsulinemia and obesity through other mechanisms. One proposed mechanism involves GLUT5

If FFA are not removed from tissues, as occurs in fructose fed insulin resistant models, there is an increased energy and FFA flux that leads to the increased secretion of TG

In these scenarios, where there is excess hepatic fatty acid uptake, synthesis and secretion, 'input' of fats in the liver exceed 'outputs', and hepatic steatosis occurs

Carbohydrate induced hypertriglycerolemia results from a combination of both TG overproduction, and inadequate TG clearance

fructose-induced metabolic dyslipidemia is usually accompanied by whole body insulin resistance [100] and reduced hepatic insulin sensitivity

Excess VLDL secretion has been shown to deliver increased fatty acids and TG to muscle and other tissues, further inducing insulin resistance

the metabolic effects of fructose occur through rapid utilization in the liver due to the bypassing of the regulatory phosphofructokinase step in glycolysis. This in turn causes activation of pyruvate dehydrogenase, and subsequent modifications favoring esterification of fatty acids, again leading to increased VLDL secretion

High fructose diets can have a hypertriglyceridemic and pro-oxidant effect

Oxidative stress has often been implicated in the pathology of insulin resistance induced by fructose feeding

Administration of alpha-lipoic acid (LA) has been shown to prevent these changes, and improve insulin sensitivity

LA treatment also prevents several deleterious effects of fructose feeding: the increases in cholesterol, TG, activity of lipogenic enzymes, and VLDL secretion

Fructose has also been implicated in reducing PPARα levels

PPARα is a ligand activated nuclear hormone receptor that is responsible for inducing mitochondrial and peroxisomal β-oxidation

decreased PPARα expression can result in reduced oxidation, leading to cellular lipid accumulation

fructose diets altered the structure and function of VLDL particles causing and increase in the TG: protein ratio

LDL particle size has been found to be inversely related to TG concentration

therefore the higher TG results in a smaller, denser, more atherogenic LDL particle, which contributes to the morbidity of the metabolic disorders associated with insulin resistance

High fructose, which stimulates VLDL secretion, may initiate the cycle that results in metabolic syndrome long before type 2 diabetes and obesity develop

A high flux of fructose to the liver, the main organ capable of metabolizing this simple carbohydrate, disturbs normal hepatic carbohydrate metabolism leading to two major consequences (Figure 2): perturbations in glucose metabolism and glucose uptake pathways, and a significantly enhanced rate of de novo lipogenesis and TG synthesis, driven by the high flux of glycerol and acyl portions of TG molecules coming from fructose catabolism

significant and clinically relevant worsening of insulin sensitivity with an isoenergetic plant-based high-protein diet

healthy humans that are exposed to amino acid infusions rapidly develop insulin resistance

longer term high-protein intake has been shown to result in whole-body insulin resistance [68, 118], associated with upregulation of factors involved in the mammalian target of rapamycin (mTOR)/S6K1 signalling pathway [68], increased stimulation of glucagon and insulin within the endocrine pancreas, high glycogen turnover [118] and stimulation of gluconeogenesis [68, 118].

it was recently shown in a large prospective cohort with 10 years followup that consuming 5% of energy from both animal and total protein at the expense of carbohydrates or fat increases diabetes risk by as much as 30% [69]. This reinforces the theory that high-protein diets can have adverse effects on glucose metabolism.

Another recent study showed that low-carbohydrate high-protein diets, used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins, are also associated with increased risk of cardiovascular disease [70], thereby indicating a potential link between high-protein Western diets, T2DM, and cardiovascular risk.

malnutrition progressing to cachexia is another common manifestation of cirrhosis

Malnutrition can be mitigated with BCAA supplementation

Studies show that administration of amino acid formulas enriched with BCAAs can reduce protein loss, support protein synthesis, and improve nutritional status of patients with chronic liver disease

Leucine has been shown to be the most effective of the BCAAs because it acts via multiple pathways to stimulate protein synthesis

BCAAs metabolites inhibit proteolysis

Patients with cirrhosis have both insulin deficiency and insulin resistance

BCAAs (particularly leucine) help to reverse the catabolic, hyperglucagonemic state of cirrhosis both by stimulating insulin release from the pancreatic β cells and by decreasing insulin resistance allowing for better glucose utilization

Coadministration of BCAAs and glucose has been found to be particularly useful

BCAA supplementation improves protein-energy malnutrition by improving utilization of glucose, thereby diminishing the drive for proteolysis, inhibiting protein breakdown, and stimulating protein synthesis

Cirrhotic patients have impaired immune defense, characterized by defective phagocytic activity and impaired intracellular killing activity

another effect of BCAA supplementation is improvement of phagocytic function of neutrophils and possibly improvement in natural killer T (NKT) cell lymphocyte activity

BCAA supplementation may reduce the risk of infection in patients with advanced cirrhosis not only through improvement in protein-energy malnutrition but also by directly improving the function of the immune cells themselves

BCAA administration has also been shown to have a positive effect on liver regeneration

A proposed mechanism for improved liver regeneration is the stimulatory effect of BCAAs (particularly leucine) on the secretion of hepatocyte growth factor by hepatic stellate cells

BCAAs activate rapamycin signaling pathways which promotes albumin synthesis in the liver as well as protein and glycogen synthesis in muscle tissue

Chemical improvement with BCAA treatment is demonstrated by recovery of serum albumin and lowering of serum bilirubin levels

long-term oral BCAA supplementation was useful in staving off malnutrition and improving survival by preventing end-stage fatal complications of cirrhosis such as hepatic failure and gastrointestinal bleeding

The incidence of death by any cause, development of liver cancer, rupture of esophageal varices, or progression to hepatic failure was decreased in the group that received BCAA supplementation

Patients receiving BCAA supplementation also have a lower average hospital admission rate, better nutritional status, and better liver function tests

patients taking BCAA supplementation report improved quality of life

BCAAs have been shown to mitigate hepatic encephalopathy, cachexia, and infection rates, complications associated with the progression of hepatic cirrhosis

BCAAs make up 20-25% of the protein content of most foods

Highest levels are found in casein whey protein of dairy products and vegetables, such as corn and mushrooms. Other sources include egg albumin, beans, peanuts and brown rice bran

In addition to BCAAs from diet, oral supplements of BCAAs can be used

Oral supplementation tends to provide a better hepatic supply of BCAAs for patients able to tolerate PO nutrition as compared with IV supplementation, especially when treating symptoms of hepatic encephalopathy

Coadministration of BCAAs with carnitine and zinc has also been shown to increase ammonia metabolism further reducing the encephalopathic symptoms

Cirrhotic patients benefit from eating frequent, small meals that prevent long fasts which place the patient in a catabolic state

the best time for BCAA supplementation is at bedtime to improve the catabolic state during starvation in early morning fasting

A late night nutritional snack reduces symptoms of weakness and fatigability, lowers postprandial hyperglycemia, increases skeletal muscle mass,[25] improves nitrogen balance, and increases serum albumin levels.[26] Nocturnal BCAAs even improve serum albumin in cirrhotic patients who show no improvement with daytime BCAAs

Protein-energy malnutrition (PEM), with low serum albumin and low muscle mass, occurs in 65-90% of cases of advanced cirrhosis

hyperglucagonemia results in a catabolic state eventually producing anorexia and cachexia

BCAAs are further depleted from the circulation due to increased uptake by skeletal muscles that use the BCAAs in the synthesis of glutamine, which is produced in order to clear the ammonia that is not cleared by the failing liver

patients with chronic liver disease, particularly cirrhosis, routinely have decreased BCAAs and increased aromatic amino acids (AAAs) in their circulation

Maintaining a higher serum albumin in patients with cirrhosis is associated with decreased mortality and improved quality of life

the serum BCAA concentration is strongly correlated with the serum albumin level