Sunday 26 July 2015

GABA: Inhibitory Neurotransmitter

A number of amino acids have direct effects in the central nervous system and can be considered as possible treatments for mental disorders. Gamma-aminobutyric acid (GABA) is one such amino acid. However although GABA is an amino acid, it is not an alpha amino acid because it is not incorporated into proteins. It is also not essential as it can be synthesised from glutamic acid in the brain using the enzyme glutamate decarboxylase. In the central nervous system GABA acts as an inhibitory amino acid which inhibits neuronal activity. Here it is released from GABAergic neurones and binds to postsynaptic GABA receptors. Ligand receptor interactions leads to a closing of chloride channels in the postsynaptic neurone. This depolarises the postsynaptic cell membrane and this in turn reduces the likelihood that an action potential will fire on the postsynaptic neurone. In this way GABA has an inhibitory effect on the postsynaptic neurones and decreases neuronal excitation.
The ability of GABA to inhibit neuronal activity explains the relaxing properties of supplemental GABA. The plasma, brain and cerebrospinal fluid of depressed subjects are low in GABA which suggests that GABA may play a role in depression. In particular, GABA may be able to effectively treat depression that is related to anxiety, as the antidepressant and antianxiety effects of benzodiazepines are likely due to their effects on the GABA neuronal systems. Some evidence suggests that depression caused by alcohol or poor dietary habits may be triggered by reductions in the GABA concentrations of the brain. Supplemental GABA is also a useful sleep aid for those without depression because it inhibits neurotransmitter activity in the brain and reduces anxiety, which may increase sleepiness. Taking GABA supplements before bed is therefore the best strategy, as this will negate the drowsiness some experience from taking GABA. Both capsules and powders appear effective at increasing brain levels of GABA.

Saturday 25 July 2015

High Carbohydrate Diets Can Be Healthy

Carbohydrate Sports Drinks and Gastric Emptying Rate

The stomach is one of the control points for digestion and absorption. The pyloric sphincter is a ring of muscle at the bottom of the stomach, which acts as a gate to the duodenum and the rest of the small intestine. Contraction of the pyloric sphincter inhibits chyme from exiting the stomach, thus delaying digestion, and particularly, absorption. Gastric emptying rate varies amongst individuals, and women tend to show slower gastric emptying compared to men. Gastric emptying rate follows an exponential time course and is related most closely to the degree of distention in the wall of the stomach muscle and the amount of undigested protein in the stomach. However, other factors do affect the rate of gastric emptying. Consideration of the rate of gastric emptying is important for sports drink consumption as rehydration during and after intense exercise should be as efficient as possible. Factors that slow the passage of water and replacement energy through the stomach are therefore worthy of discussion.
The volume of the drink and its concentration are known to influence the gastric emptying rate. As volume increases up to 700 mL the gastric emptying rate increases. Maintenance of a high gastric volume therefore aids rehydration. This should equate to consumption of around 200 mL of liquid every 15 minutes during intense exercise. As around 1 to 2 litres of water can be lost through sweat during intense exercise, this rate of drinking can almost keep pace with the most extreme loss of water from sweat. Addition of glucose or other some sugars to exercise drinks increases the osmolarity and this can reduce gastric emptying rate. However, fructose appears not to present the same inhibitory effect on gastric emptying, which is why consumption of fruit drinks and soft drinks containing fructose may be particularly bad for the health. Maltodextrins are chains of glucose that vary in molecular weight. Addition of maltodextrin to water does not increase osmolarity to the same effect as an equal weight of glucose.
Even taking into account the different osmolarities of different sugars, the literature generally shows that carbohydrate solutions of around 4 to 8 % carbohydrate, regardless of carbohydrate type, do not cause changes in gastric emptying compared to water. However, above this percentage gastric emptying rate is inhibited and this will affect the ability of the drink to keep pace with water loss. Commercial sports drinks tend to have sugar contents above this 8 % ceiling which is why they should either be diluted with water, or avoided. The duodenal brake that is the pyloric sphincter is important physiologically because it is there to provide a safety valve to prevent a large oversupply of energy to the liver, which may cause detrimental metabolic shifts. Interestingly the bypassing of this break by consumption of fructose is a possible cause of the liver overload syndrome, which may be required to cause obesity. Consuming commercial high sugar sports drink outside of exercise is particularly detrimental.

Sunday 19 July 2015

DHA for Brain Health

Docosahexaenoic acid (DHA) is a long chain polyunsaturated fatty acid found in fish. It is a member of the omega-3 family of fatty acids and can be converted to eicosapentaenoic acid (EPA) in humans. Eicosapentaenoic acid is important nutritionally because it can be converted to the series 3 eicosanoids (including thromboxanes, prostaglandins) and the series 5 leukotrienes, and these have overall anti-inflammatory effects. Inflammation is able to increase levels of oxidative stress and it is this oxidative stress that may drive many of the Western lifestyle diseases. Ensuring adequate intake of omega-3 fatty acids, in a balanced ratio to the omega-6 fatty acids, is therefore pivotal at inhibiting inflammation, oxidative stress and disease. As a deficiency of omega-3 fatty acids can increase inflammation in the brain, with a concomitant increase in oxidative stress, mental and cognitive deterioration may be related to an underlying omega-3 fatty acid imbalance. The typical Western diet is characterised by such an imbalance.
However, DHA may have protective properties on brain tissue other than in its role as a precursor to EPA. Evidence is accumulating to show that DHA is pivotal in brain development during foetal development and childhood. For example, breast fed infants have been shown to have better mental health that formula fed infants, breast milk being particularly high in DHA. In addition, low levels of DHA are associated with depression, although the cause and effect of this relationship is not understood. Supplementation of DHA to pregnant mothers also increases the problem solving ability of their infants postpartum. The role of DHA in mental health may relate to its conversion to a series of not classical eicosanoids including the resolvins and docosatrienes. These fatty acid derivatives appear important for neuronal health and function. Low levels of DHA may therefore modulate neuronal physiology and create brain imbalances and ill health. Algal sources of DHA are available to vegetarians.

Saturday 18 July 2015

Alcohol Alters Eicosanoid Metabolism

Alcohol is known to have health benefits in humans. Consuming alcoholic beverages may provide some health benefits because of the phytochemicals within the drinks. These phytochemicals are derived from the fruits used to make the drinks. For example, cider contains apple polyphenols that are bioactive and have been shown to have beneficial health effects. Red wine is a highly complex mixture of plant derived phytochemicals including polyphenols that may have particular health benefits. However, administration of the ethanol component of alcoholic drinks in the absence of any plant phytochemicals still confers protective health effects, suggesting that ethanol itself is beneficial. One of the most widely reported health benefits of ethanol is to the cardiovascular system. Drinking alcohol for example reduces the risk of a heart attack significantly in the proceeding 24 hours. The cardioprotective effects of ethanol have studied by and may relate to the effect ethanol has an essential fatty acid metabolism.
For example, in one study1, the effects of ethanol on the production of prostaglandin E1 and thromboxane B1 was investigated in human platelets. Ethanol in the 33 to 300 mg per 100 mL plasma caused a significant dose response increase in the conversion of dihomo-gamma-linolenic acid to both prostaglandin E1 and thromboxane B1. However ethanol at the same concentrations had no effects on the conversion of arachidonic acid to prostaglandin E2 and thromboxane B2. Prostaglandin E1 and thromboxane B1 have anti-inflammatory and antithrombotic effects respectively, while prostaglandin E2 and thromboxane B2 have pro-inflammatory and prothrombotic effects, respectively. This may explain some of the cardioprotective effects of ethanol. The authors suggested that the effects of ethanol could be due to improved transport of the dihomo-gamma-linolenic acid to the active site of the cyclooxygenase enzyme required to catalyse the synthesis of prostaglandins and thromboxanes.
1Manku, M. S., Oka, M. and Horrobin, D. F. 1979. Differential regulation of the formation of prostaglandins and related substances from arachidonic acid and from dihomogammalinolenic acid. I. effects of ethanol. Prostaglandins and Medicine. 3(2): 119-128

Sunday 12 July 2015

Oysters: Nutrient Dense Seafood

Edible oysters belong to two different genera. The Ostrea and Crassostrea differ in appearance but have similar tastes. While the Ostrea have round and scalloped shells, the Crassostrea have shells that are long and asymmetrical. Crassostrea virginica and Crassostrea gigas are Atlantic and Pacific oyster, respectively. Ostrea lurida is found in the pacific while Ostrea edulis is found in the coastal waters of Great Britain. Oysters are bivalves, with two roughly equal hard fluted shells encasing a soft inner body. Generally oysters have a creamy texture and a salty taste, but the state of oysters can differ based on the temperature of the water in which they live. Generally colder water species have superior raw tastes, but it is generally accepted that once cooked the taste difference is not noticeable. The salinity of the water, its mineral content and the chlorophyll content of the plankton in the water and all affect the taste of the oysters. Cooking must be achieved slowly or the texture of the body turn tough.
Oysters have the highest zinc content of any food at roughly 35 mg per 100 gram serving. The same 100 gram serving would also contain roughly 550 mg of the polyunsaturated fatty acid eicosapentaenoic acid and a similar amount of the polyunsaturated fatty acid docosahexaenoic acid. The fat within oyster is therefore highly unsaturated omega-3 fat, although there is around 105 grams of cholesterol per 100 grams. Vitamin B12 is also present in oysters in reasonable quantities as are the minerals copper, iron and selenium. However, as with all organic life, the mineral content of the tissues depends to a large extent on the mineral composition of the environment in which the organism lives. The historical use of oysters as an aphrodisiac likely relates to the zinc content, zinc being required for proper male reproductive function. Because oysters spoil quickly, it is best to only eat them quickly. Oysters have a superior taste in the autumn winter and early spring before they spawn and become less tender.

Saturday 11 July 2015

Docasonoids And Brain Health

Increasingly diet is being linked to the health of the brain. In particular, consumption of the typical Western diet may increase the risk of neurological age related degeneration. The reason for this may be numerous, but certainly one factor that is currently being researched is the ability of the Western diet to produce pro-inflammatory effects in brain tissue. Such inflammation may lead to excessive free radical generation, and this oxidative stress may cause degradation of the delicate unsaturated fats that predominate in the brain. Fish oils and other sources of omega-3 fatty acids may protect the brain form d'generation because they increase the eicosapentaenoic acid content of cell membranes. This eicosapentaenoic acid acts as a reservoir for the synthesis of anti-inflammatory series 3 eicosanoids that may decrease the inflammation in the brain tissue. However, as well as eicosanoids, docosanoids may also play a role.
Docosanoids are short lived hormone molecules derived from docosahexaenoic acid. Docosahexaenoic acid is a component of fish oil and is also able to be synthesised from other sources of omega-3 fatty acids. Evidence suggests that docosahexaenoic acid accumulates in cell membranes, and is particularly concentrated in the membranes of neurones in the central nervous system. Here the fatty acid acts as a reservoir for the production of docosanoids, short lived chemical messengers that may regular neurotransmission and other neuronal functions. For example the docosanoid neuroprotectin D1 has been shown to inhibit the apoptosis of neurones exposed to oxidative stress. Docosanoids may also be involved in the maintenance of correct serotonin metabolism and aid in memory and learning. The presence of docosahexaenoic acid is fish therefore justifies the classification of fish as a brain food.

Sunday 5 July 2015

Type 1 Diabetes And Vitamin D

There are two main forms of diabetes. Type 2 diabetes is thought to result from poor quality diet and too little exercise. In particular, the Western diet and Western lifestyle is thought to contribute significantly to the development of type 2 diabetes. Poor diet and a lack of exercise causes a reduction in insulin sensitivity that over time worsens and leads to insulin resistance. Insulin resistance in turn leads to excessive insulin secretion and increases in fasting insulin levels, which results in blood sugar aberrations. Over time the stress of this dysfunction damages the pancreas and can result in insufficient insulin production and release. Type 1 diabetes is different to type 2 diabetes, because it is thought that the pancreas is damaged not by overworking, but through an autoimmune reaction that destroys the insulin producing beta cells. However, there is strong evidence that this effect might also be nutritionally linked. Certain proteins in the diet and a lack of vitamin D are thought to be involved.
What triggers the autoimmune response in type 1 diabetes has been investigated. Two culprits that have been identified include proteins in cow’s milk (bovine serum albumin and bovine insulin) as well as the wheat protein gluten. Antigens on these proteins might be recognised as foreign, and their similarity to antigens on the surface of beta cells in the pancreas may initiate destruction of the beta cells by the immune system. Evidence suggests that those not exposed to cow’s milk in early years because they are breast fed may have a reduced risk of developing type 1 diabetes. Poor vitamin D status has been shown to be associated with an increased risk of developing type 1 diabetes, and this might relate to the function of vitamin D at modulating immune response. That breast milk is a good source of the biologically active form of vitamin D, 25-hydroxyvitamin D, and is also able to support proper gut development and immunity, suggests that early reliance of cow’s milk may play a role in the development of type 1 diabetes.

Saturday 4 July 2015

Seven Reasons why Cholesterol Testing is Pointless

Cholesterol testing is big business, which perhaps explains why it is so widespread. Certainly the actual point of testing the blood cholesterol of large numbers of the population has little benefit and is little to do with science. Cholesterol testing has a place, and in a research setting it can be highly useful. However, in research more expensive tests and finer detail are extracted from the testing process making it relevant. The tests for total cholesterol that are common in the medical setting are actually quite useless. Here are seven reasons why.
1. Total Blood Cholesterol is Meaningless
Measuring total cholesterol in the blood is pointless. This is because is is quite a weak indicator for cardiovascular disease. In fact in certain groups, particularly the elderly and in women, higher levels of total cholesterol can be associated with a decreased risk of mortality. Extrapolating ranges for total cholesterol levels to the population as a whole is therefore quite pointless unless it takes into account the person being tested, which of course never happens.
2. Low Density Lipoprotein (LDL) is A Better Biomarker Than Total Cholesterol
Some tests now include the LDL fraction. The LDL fraction is a better biomarker for cardiovascular disease than total cholesterol, with high levels of LDL increasing the risk of cardiovascular disease. However, LDL is made up of different particles that can be subgrouped into the small dense fraction and the large buoyant fraction. Only the small dense LDL fraction is associated with cardiovascular disease but clinical tests do not differentiate between the two.
3. What About High Density Lipoprotein (HDL)
Some clinical tests now measure levels of HDL as well as LDL and total cholesterol. The HDL fraction is actually protective of cardiovascular disease and so the ratio between the HDL and LDL fraction is a better predictor of cardiovascular risk compared to either LDL or total cholesterol in isolation. However, without knowing with sort of LDL dominates the reading (small dense or large buoyant) you cannot accurately predict cardiovascular risk.
4. Lipoprotein(a) is Highly Atherogenic
There is another lipoprotein particle that is almost never mentioned and which will not be included in a clinical test. Lipoprotein(a) is highly atherogenic and is a very strong predictor of cardiovascular risk. Even more so that the HDL to LDL ratio. Its exclusion is problematic because even with a normal level of blood cholesterol, high concentrations of lipoprotein(a) would increase your risk of cardiovascular disease significantly. Some researchers claim lipoprotein(a) has been mistaken for LDL in studies, confusing the matter further.
6. Homocysteine Levels
Homocysteine is a metabolite of methionine metabolism. High homocysteine blood levels are a strong predictor of cardiovascular disease. Homocysteine is not routinely tested for and a person could have normal levels or cholesterol, a favourable HDL to LDL ratio and still be at high risk of cardiovascular disease because of elevated plasma homocysteine levels. Unless a homocysteine test is undertaken, it is difficult to predict cardiovascular risk.
7. Cholesterol is Associated with Cardiovascular Disease, It Does Not Cause It
High levels of total cholesterol and an unfavourable LDL to HDL ratio (favouring the small dense LDL particle) are risk factors for cardiovascular disease. However, they do not cause, but are merely associated with it. The cause of cardiovascular disease and lipoprotein changes are likely insulin resistance. Receiving a diagnosis and taking a pill to lower cholesterol levels therefore does nothing to reduce the risk of cardiovascular disease without addressing the underlying insulin resistance.