"...re-synthesis after short term, high intensity exercise (15.1 to 33.6 mmol/kg/h) is much higher than glycogen re-synthesis rates following prolonged exercise (approximately 2 mmol/kg/h), even when optimal amounts of oral carbohydrate are supplied (approximately mmol/kg/h)." My take on this article, and the fast food, more liberal repletion concept?
In their natural setting, cats—whose unique biology makes them true carnivores–would not consume the high level of carbohydrates (grains, potatoes, peas, etc.) that are in the dry foods (and some canned foods) that we routinely feed them. You would never see a wild cat chasing down a herd of biscuits running across the plains of Africa or dehydrating her mouse and topping it off with corn meal.
normal which leads to muscle loss and the inability to maintain adequate muscle tone. Also, in the absence of adequate carbohydrate for fuel, the body initially uses protein (muscle) and fat. the initial phase of muscle depletion is rapid, caused by the use of easily accessed muscle protein for direct metabolism or for conversion to glucose (gluconeogenesis) for fuel. Eating excess protein does not prevent this because there is a caloric deficit. When insulin levels are chronically too low as they may be in very low carb diets, catabolism (breakdown) of muscle protein increases, and protein synthesis stops.
Although it had been originally been suggested in 1992 that the to a carbohydrate supplement would enhance the rate of muscle glycogen re synthesis after endurance exercise, provided evidence that the difference was not protein per se, but the fact that the two drinks were not Calorically equal.
Protein synthesis involves building a polymer of amino acids with complex three-dimensional structure. Dehydration synthesis forms a between amino acids and releases a water molecule. A forms when a peptide bond is created between two individual amino acids, connecting the carboxyl-group carbon of one amino acid and the amino-group nitrogen of another amino acid. As additional amino acids are bonded through dehydration synthesis, a short chain () grows. are formed as peptide chain lengths reach one hundred or more amino acids. Proteins form as amino acids in one or more polypeptides chemically interact to create a complex three-dimensional structure.
Dietary protein is not used efficiently as a source of energy. Although the gross energy of protein is greater than that of carbohydrate (23.6 kJ/g v 17.4 kJ/g for starch), when protein is used as an energy source the N has to be excreted as ammonia (fish), urea (mammals) or uric acid (birds). The ME value of protein at zero N retention takes into account the loss of energy in the excreta, such that the ME of protein and carbohydrate are approximately similar. The ME value for mammals and birds, however, does not take into account the energy costs of synthesising urea or uric acid and the cost of excretion in the kidney. Net energy (NE) of the diet represents the useful energy used to replace the losses of maintenance and the net deposition of energy as new tissue in growth or milk secretion during lactation, after subtracting the heat losses of metabolism.
1. Low carb (ketogenic) diets deplete the healthy glycogen (the storage form of glucose) stores in your muscles and liver. When you deplete glycogen stores, you also dehydrate, often causing the scale to drop significantly in the first week or two of the diet. This is usually interpreted as fat loss when it's actually mostly from dehydration and muscle loss. By the way, this is one of the reasons that low carb diets are so popular at the moment - there is a quick initial, but deceptive drop in scale weight. Glycogenesis (formation of glycogen) occurs in the liver and muscles when adequate quantities of carbohydrates are consumed - very little of this happens on a low carb diet. Glycogenolysis (breakdown of glycogen) occurs when glycogen is broken down to form glucose for use as fuel.
Differences between species in their digestive system also affect the required concentration of protein. Carnivores have no ability to digest fibrous feed and even a limited ability to digest starchy carbohydrates. Consequently, the diet has to contain more of both protein and fat, but the protein: energy ratio is not greatly increased compared with pigs and poultry. Fish appear to have much higher protein needs than mammals and aquaculture diets (a very important area in developing countries) are high in protein. To a large extent this is not due to a greater need for protein but a smaller need for energy. Poikilothermic animals (fish, reptiles) do not need energy to maintain their body temperature, whereas homoiothermic animals (birds and mammals) expend a considerable amount of energy (partly reflected as basal metabolic rate and maintenance energy, and partly as shivering or panting) to maintain a constant body temperature different to the environmental temperature.
Protein synthesis in the body involves a considerable expenditure of energy to create the activated amino acids to be linked together. In addition, protein tissues are constantly being turned over. For every one unit of net accretion of protein about 5 units of protein are synthesised. Some tissues are turning over faster than others. Indeed some of the fastest tissue replacement, such as in the intestinal epithelium and liver, lead to little or no net accretion. The energy cost of protein synthesis in protein turnover, just to maintain the existing protein, has been estimated to account for 15 to 33 percent of energy needed for maintenance. When additional energy is provided, there is an increase in protein synthesis and a decrease in protein degradation and these two effects combine to enhance net protein retention. When additional protein is supplied at constant energy, there is an increase in both protein synthesis and in protein degradation, resulting in a smaller net increment in protein retention. This is illustrated in Figure 5, which gives the determined synthesis and degradation contributions to the net N retention. With increasing protein in the diet there are frequently small improvements in carcase quality, measured as increased protein and decreased fat content. These changes arise from the decreased net energy value of protein compared with carbohydrate and the increased energy required for increased protein turnover driven by higher dietary protein intake, resulting in reduced energy available for fat synthesis.
Consequently, if the requirement for one amino acid is determined by empirical trial in one situation, the requirements for all the others can be estimated by applying the ratio as determined for the ideal protein. Because lysine is normally the first limiting amino acid in most practical diets and therefore the requirements for lysine were the most studied in empirical trials, lysine is used as the reference amino acid and all others are expressed as a ratio to lysine (Table 2). A first approximation to the ideal ratio is the amino acid composition of the whole body, or of the tissue protein gained during growth. This makes the assumption that each absorbed indispensable amino acid is used with the same efficiency for protein synthesis. This is not true since some amino acids e.g. tryptophan and methionine are used for purposes other than protein synthesis, and others such as cystine and threonine have large losses in intestinal mucoproteins. Also as different proteins turn over at different rates, the ideal pattern changes with change in proportions of the different proteins being synthesised at any one time. For example, as the proportion of protein involved in maintenance of the body compared with accretion of new tissue changes with age, so the ideal pattern will change to reflect the different proteins involved. Consequently, the ideal pattern has evolved in recent years as some of these factors have been studied. Given an accurate determination of the lysine requirement in terms of percent of diet or g/MJ ME in any given situation, the requirement for the remaining indispensable amino acids can be calculated.