Sunday, 27 September 2015
L-glutamine is available in powder form and is a popular supplement. The bioavailability of oral glutamine has been questioned because much of the oral glutamine is utilised as a source of energy by the enterocytes of the small intestine. Glutamine can also be released from skeletal muscle in large amounts and this too it utilised by the enterocytes of the small intestine. For this reason oral glutamine is seen as being useful to those with particular gastrointestinal disorders where enterocytes may require a sufficient supply of energy. Cabbage is a good source of glutamine, and its use in the treatment of gastrointestinal lesions is well reported. Oral glutamine may protect the enterocytes from radiation, and rat experiments have shown that oral glutamine can protect irradiated rats from some of the symptoms associated with radiation poisoning including diarrhea and intestinal bleeding. The gut healing properties of oral glutamine are therefore quite well established.
Because of the use of oral glutamine by the gut, little of the orally taken glutamine makes it to the circulation. However, by ingesting oral glutamine, some of the glutamine released from the skeletal muscle may not be used by the gut cells and in this way oral glutamine may raise plasma levels of glutamine indirectly. In this regard oral glutamine before exercise may significantly increase plasma levels of glutamine, as this is a time when skeletal muscle catabolism and release of glutamine to the blood is elevated. The release of glutamine from skeletal muscle is a result of the metabolic acidosis caused by intense exercise. In this role the glutamine is used for base generation by the kidneys. Oral glutamine can therefore decrease muscle catabolism following exercise as there is less need for the muscle glutamine as endogenous supplies are able to supply the substrate for base generation. Animal and human studies show that oral glutamine may therefore be an effective ergogenic aid.
Oral glutamine may also enhance the activity of natural killer cells, and thus have an immune stimulatory effect. The use of glutamine in large amounts by other immune cells including lymphocytes and macrophages suggests that immunity benefits from oral glutamine supplementation if plasma levels rise. Because oral glutamine has an anti-catabolic effect on skeletal muscle, it may be a useful supplement for those with chronic wasting diseases. However, the daily production of glutamine in humans is thought to exceed 100 grams in some cases and therefore small doses orally, most of which would be consumed by the enterocytes of the gut, may not be effective. Glutamine is interconvertible to glutamic acid through loss of a nitrogen group (to form ammonia). Food labels tend not to list glutamine levels separately but list the glutamic acid content as including glutamine. Roughly 50 % of the glutamic acid in animal protein is glutamine, and around 80 % of the glutamic acid in plant proteins are glutamine.
Saturday, 26 September 2015
Glycine is the simplest amino acid in human nutrition. The variable group on glycine is composed of just a hydrogen atom and as such L-glycine is the only amino acid in human nutrition that does not demonstrate chirality. Glycine is a non-essential amino acid as it is syntesised from serine and threonine, the latter being an essential amino acid. When taken orally, glycine has a particular sweet taste. Glycine is used metabolically to synthesise purine, porphyrins, glyoxylic acid and creatine. With regards to creatine, glycine and arginine react in the synthesis of creatine, which is subsequently phosphorylated to form the ATP buffer creatine phosphate in cells. Supplements of glycine and arginine are able to increase muscle stores of creatine phosphate, in a similar manner to ingestion of creatine monohydrate supplements. However, while creatine monohydrate supplies the creatine directly, glycine and arginine increase endogenous creatine synthesis rates.
Glycine is also involved in the synthesis of collagen, of which it constitutes around 75 % of the amino acids. Much of the remaining amino content of collagen is taken by proline. Glycine is therefore pivotal to correct join function, although most people consume enough protein in their diet and therefore have an adequate supply of glycine for collagen formation. Collagen however is the most abundant protein in the body and this highlights the importance of glycine. High intakes of up to 10 grams of glycine orally may be able to stimulate growth hormone release. Following oral supplements growth hormone levels rise and peak at around 3 hours. However, it is unclear if the increase in growth hormone has beneficial physiological effect. For example, it is not known whether the glycine induced growth hormone release has an anti-catabolic effect on skeletal muscle. Glycine is also converted to dimethylglycine, which has an important function in the formation of steroid hormones.
Glycine is also an important neurotransmitter in the brain, where it functions as an inhibitory neurotransmitter. Its inhibitory effects in the central nervous system may provide beneficial effects against seizures and epilepsy and may be of some clinical use in treating some mental disorders. Glycine appears to have antiinflammatory and immunomodulatory effects because it can act of immune cells such as macrophages to inhibit cytokine release. Studies have shown that supplemental glycine may be of benefits in cases of fatigue, perhaps because if its creatine synthesising effects. Glycine can also help regulate fat metabolism because it aids in the modulation of bile acid formation. Its sweetness means that glycine also possesses some use in treating type 2 diabetes and obesity by acting as a potential sweetener in place of sugar. Because glycine can be manufactured in the body deficiencies are very rare. Glycine is also commonly found in most protein containing foods and so is abundant in the diet of humans.
Sunday, 20 September 2015
Eggs are considered detrimental to the health by many because of their high content of cholesterol and saturated fat. However, the role of the egg in human nutrition has been distorted considerably. This is particularly true when considering the types of lipids in chicken eggs. Eggs are a rich source of cholesterol for example, but the role of cholesterol in cardiovascular disease has been misunderstood. While an association exists between plasma levels of some cholesterol carrying lipoproteins and cardiovascular disease, the cause and effect has never been conclusively evidenced. Rather like a fire engine being present at the scene of an accident, no sane person would conclude that fire engines are the cause of accidents. As with cholesterol, its presence in the plasma and accumulation in the atherosclerotic plaque do in no way implicate it as the causative in cardiovascular disease. Further, dietary intakes of cholesterol are not able to alter plasma levels of cholesterol and so the point is quite moot.
The saturated fat content of eggs has also been misunderstood. Eggs from battery chickens do contain high amounts of saturated fat, and this relates to the sterile grain diets these birds are fed to allow them to be farmed intensively. However, free range chicken eat their natural diet which contains many varied foods including insects and parts of plants. This gives the nutritional content of the egg a quite different appearance. In particular, the saturated fat in the free range egg is replace to some extent by the omega-3 fatty acid alpha linolenic acid. As most Westerners consume too little omega-3 fat, eating free range eggs is a good way to rebalance this deficiency. Further alpha linolenic acid, like other dietary omega-3 fatty acids, may be cardioprotective. That the role of saturated fat in cardiovascular disease has not been conclusively evidenced adds weight to the contention that eggs from healthy free range chickens are not detrimental to the health of the cardiovascular system.
Chicken eggs are also a very good source of protein, and this gives them some useful nutritional properties. Protein is increasingly being seen as a weight loss food. This may relate to the ability of protein to slow the passage of starch through the gut, particularly the stomach, which in turn confers beneficial glycaemic effects. These glycaemic effects reduce the release of insulin and this may produce benefits to satiety, wakefulness and energy production. Consuming eggs for breakfast with starchy foods such as bread or oats therefore produces desirable effects on blood sugar that may reduce the risk of overeating between meals. Regulating blood sugar by controlling insulin levels may improve mental focus because lower insulin levels reduce the transport of blood L-tryptophan into the brain, which can then subsequently be converted to serotonin and melatonin. As melatonin induces sleepiness, higher protein lower starch breakfasts may effectively increase productivity in the early morning through increased wakefulness.
Saturday, 19 September 2015
Biologically salmon are amazingly adaptable. They are born in fresh water, spend much of their lives in open sea, and then return to the river of their birth to spawn. A number of different varieties of salmon exist, with the exact classification depending largely on the oceans in which they spend most of their lives. For example, pacific salmon belong to the genus Oncorhynchus and include chinook, silver (coho), chum, pink and red (sockeye). There is only one variety of Atlantic salmon which is Salmo salar. The characteristics of salmon vary with the species, and in particular the colour of the flesh can be different. Generally the colour of the flesh of salmon range from pink through red to orange. The taste and size of the fish can also vary between the species, with chinook salmon being the largest and red salomon being the smallest. Although wild salmon is fished from the seas around Alaska, much of the commercially available fish is farmed, particularly in places such as Scotland, Canada and Norway.
Salmon has historically been an important protein food for humans. In this regard salmon is often salted or smoked in order to preserve it. As well as providing a high protein content, salmon also possesses a high concentration of long chain fatty acids of the omega-3 family including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty acids are increasingly being found to benefit health because they are deficient from the typical Western diet, and addition of them to the diet corrects the naturally low levels found in most individual’s diets. Wild salmon tends to contain more fat and is therefore richer in energy, but as the fat in salmon is beneficial to the health, this can be seen as an advantage. In addition, farmed salmon has a lower protein content compared to wild salmon. Concerns over dangerous levels of toxins in farmed salmon have also been voiced. Like most seafood, salmon is also a good source of the mineral selenium, and also contains vitamin B12 and niacin.
Sunday, 13 September 2015
It is becoming increasingly common for infants to be fed using infant formulas. These formulas are developed scientifically to allow adequate nutrition to infants as they grow. However, they are commercial products and are therefore possess compromises that could be considered to detract from the overall quality. Generally infant formula milk is successful at allowing growth and development of healthy human beings. Most people who have been fed on infant formulas appear healthy and happy as adults. However, the definition of true health is more specific than the broad definition given by the laymen or medical practitioner. In this regard, formula milk has been criticised nutritionally for falling short in a number of areas in comparison to human milk. Evidence in the nutritional literature suggests that human breast milk is a superior food in comparison to cow’s milk based formulas for the growth of human beings. This relates to the presence of a number of factors that are not present in cow’s milk.
The most important of the components present in human milk but absent from cow's milk formulas is docosahexaenoic acid (DHA). Docosahexaenoic acid is a long chain polyunsaturated fatty acid required for the correct development of the brain and central nervous system. Increasingly it is being shown that exposure of the foetus and growing infant to DHA is required for the optimal development of the brain. Further certain cognitive aspects of breast fed infants appear to be superior to those who were fed cow’s milk formulas. Analysis of the function of DHA in humans shows that the fatty acid preferentially accumulates in the brain tissue, where it appears to be required to form a number of docosanoids that are required for neuronal function and neuronal health. The polyunsaturated fatty acids in human milk therefore appear to have beneficial neurological effects. These fats are not present in cow’s milk based formulas because they quickly go rancid following processing, and as such are removed from the milk.
Another factor that may make human milk superior to cow’s milk for infants is the presence of particular growth factors within the milk. Both human and cow’s milk contain growth factors that act as prebiotic foods that stimulate the growth of particular bacteria. However, whilst the growth factors in cow's milk stimulate Bifidobacteria species relevant to cow’s health, the growth factor in human milk stimulate Bifidobacteria species relevant to human health. Further, pasteurisation and freeze-drying destroy the activity of these factors and so although cow’s milk possesses growth factors they do not survive to the formula milk. Breast milk on the other hand is fresh and unpasteurised so that it is able to stimulate the growth of potentially beneficial bacteria that may be required for the correct development of the immune system in the growing infant. This may explain the protective effect of breast milk against the development of particular Western diseases in humans that may develop later in adult life.
Saturday, 12 September 2015
The short answer is no they do not. The long answer is more complicated because some studies that have reported blood cholesterol altering effects from increasing dietary consumption of eggs may not have controlled for confounding variables adequately. In particular changes to the energy, fibre or polyunsaturated fat intakes can all confound the data if they are not carefully controlled. Well controlled studies have generally shown that eggs do not cause changes to blood cholesterol levels in healthy humans. For example, one study added one egg per day1 and another study 2 eggs per day2, to a normal but low cholesterol diet for 3 months and found no significant response to serum cholesterol levels. In another study, two eggs per day were added to the diets of hospitalised patients for 54 days but no changes to serum cholesterol levels occured3. A fourth study added two eggs per day to the normal egg containing diet of healthy men and then removed all eggs from the diet, but this did not alter blood cholesterol levels4.
1Porter, M. W., Yamanaka, W., Carlson, S. D. and Flynn, M. A. 1977. Effect of dietary egg on serum cholesterol and triglyceride of human males. American Journal of Clinical Nutrition. 30(4): 490-495
2Flynn, M. A., Nolph, G. B., Flynn, T. C., Kahrs, R. and Krause, G. 1979. Effect of dietary egg on human serum cholesterol and triglycerides. American Journal of Clinical Nutrition. 32(5): 1051-1057
3Kummerow, F. A., Kim, Y., Hull, J., Pollard, J., Ilinov, D. L. 1977. The influence of egg consumption on the serum cholesterol level in human subjects. American Journal of Clinical Nutrition. 30(5): 664-673
4Slater, G., Mead, J., Dhopeshwarkar, G. and Alfin-Slater. 1976. Effect of eating eggs on plasma cholesterol levels in young and middle aged men. Nutrition Report International. 14: 249
Sunday, 6 September 2015
Polyunsaturated fatty acids are a double edged sword. On one hand, polyunsaturated fatty acids may hold particular health benefits. However, on the other hand, because of their chemical structure they are particularly prone to rancidity and in this form can actually be a driver of disease. It is therefore essential that all polyunsaturated fatty acids are in their natural unoxidised state in order to confer health benefits. This means that refined ‘supermarket’ oils should be avoided as these are exposed to both light and heat during processing and this can increase the amount of damaging lipid peroxides found in the oils. Plant materials containing polyunsaturated fatty acids should alway be cold pressed and the resulting oils stored in opaque bottles if they are to be healthy. In addition, the natural vitamin E content of the original plant material must remain with the oil to protect the delicate fatty acids. Further, where high intakes of polyunsaturated fatty acids are consumed additional vitamin E is advised.
Although evidence suggests that polyunsaturated fatty acids confer health benefits in humans and may protect from cardiovascular disease, the benefits really relate to the omega-3 polyunsaturated fatty acids found in fish and specific plant foods such as hemp and flax. Already the omega-6 fatty acid content of most diets consumed by Western populations is too high, and this creates an imbalance in the metabolic pathways involving the polyunsaturated fatty acids. The recommended ratio of omega-6 to omega-3 fatty acids is around 3 to 1, but even this ratio may be too heavily stacked in favour of the omega-6 oil. Evidence from Eskimo studies shows that their ratio is closer to 1 to 2.5 in favour of the omega-3 fatty acids. This very high intake of omega-3 fats may explain their very low risk of cardiovascular disease, and casts doubt on the accepts 3 to 1 ratio. As with all nutritional theory, trial and error may therefore be the best way to obtain the correct ratio for an individual's unique biochemistry.
Saturday, 5 September 2015
Consumption of high intakes of alcohol can cause damage to the liver if consumed in high amounts over long periods of time. In addition alcohol can induce certain vitamin deficiencies, particularly thiamine, and can cause changes to cognition, motivation and memory. The role of alcohol is preventing cardiovascular disease is controversial, mainly due to the dose response relating to its consumption. Generally low and high intakes do not produce beneficial effects, but moderate consumption has been shown to produce beneficial effects. The benefits of alcohol in terms of cardioprotection have been suggested to relate to its ability to raise plasma levels of high density lipoprotein (HDL). However, alcohol consumption raises levels of HDL2, a fraction that is not associated with a reduced risk of cardiovascular disease. More likely alcohol decreases the thrombotic tendencies of blood cells, an effect that is thought to provide a reduction in myocardial infarction risk for 24 hours post consumption.
Even low intake of alcohol may induce left ventricular hypertrophy and this could suggest that all alcohol is bad for the health. As few as two drinks per day if consumed regularly may produce changes to the heart structure around the left ventricle. Such hypertrophy of the left ventricle is associated with detrimental rhythmic changes to the hearts beating pattern and may increase the risk of sudden cardiac death. This effect appears to show a dose response and so higher intakes of alcohol significantly accelerate the structural changes. These structural changes to the heart are magnified if other risk factors such as high blood pressure or obesity are present. Left ventricular hypertrophy is often detected with electrocardiograms or the more sensitive echocardiograms. Left ventricular hypertrophy likely occur from drinking alcohol because alcohol consumption can increase blood pressure. If this is true it would suggest that other lifestyle habits can modify the association.
Exercise is also known to cause left ventricular hypertrophy. This is a physiological response to the increased demands on the heart for the circulation of blood during physical activity. Just why the left ventricular hypertrophy associated with drinking is detrimental, but that associated with exercise is beneficial, is never fully explained. This likely relates to the fact that those who consume alcohol and who experience left ventricular hypertrophy often have other lifestyle habits that increase the risk of cardiovascular disease. In contrast those who exercise regularly likely have other lifestyle habits that protect from cardiovascular disease. The left ventricular hypertrophy associated with exercise is also not associated with high blood pressure. Although exercise raised blood pressure during activity, following activity blood pressure falls such that the baseline level is lower than in non exercising controls. However, alcohol raises blood pressure, and this is a serious risk factor for cardiovascular disease and sudden death.