With nutrition often the most obvious solutions to problems are overlooked. This is certainly the case with the link between blood glucose levels and mood. The brain is a highly complex organ, and one that uses a large amount of energy. This energy is supplied to the brain almost exclusively as glucose. The brain obtains its glucose, like all organs, from the blood. The amount of glucose in the blood can therefore dictate how the brain functions and this in turn can dictate mood. Because of the sensitivity of the brain to fluctuations of glucose in the blood, the body tries to maintain blood glucose levels within a narrow window. It does this using the hormones insulin and glucagon. Insulin is released following ingestion of food, and the purpose of this insulin release is to transport the newly delivered glucose from the blood into cells and thereby lower blood glucose. Between meals, glucagon is released, and the function of glucagon is to raise blood glucose levels by causing the breakdown and release of stored glucose in the liver.
Insulin and glucagon work together to keep blood glucose levels within a narrow window. In this regard, these two hormones make constant fine adjustments to maintain their homeostatic control over blood glucose levels. In normal healthy individuals, this antagonistic and sensitive hormonal control leads to a stable blood sugar level, and this provides a constant and consistent delivery of glucose to the organs, including the brain. However, if the blood glucose levels are allowed to become elevated or depressed either acutely or chronically, this can have a detrimental effect on the energy supply delivered to the brain. Such fluctuations in energy supply to the brain may be a possible contributory factor in the development of mood disorders. The Western diet is likely a significant factor that leads to poor blood sugar control, and consumption of the typical Western diet may cause detrimental effects to blood glucose levels because the diet contains too much refined sugar and starch, which is absent of its original fibre content.
Refined carbohydrates can lead to addiction because they cause detrimental changes to neurochemistry. Sugar dependency, is a term used to describe the addictive behaviour displayed by rats fed highly refined sugar and starch.
In the short term, consumption of refined carbohydrate can lead to poor glycaemic control. The fibre present in unrefined sources of starch and sugar tends to reduce the rate that glucose is digested and absorbed to the blood. This facilitates a slow release of glucose to the blood, and this slow trickle of glucose is conductive to good blood sugar control because the correct amount of insulin can more easily be released to match the delivery of glucose. However, in the absence of fibre, too much glucose is delivered to the blood, and this tidal wave of glucose overwhelms the body. The blood sugar levels rise far too high, and in response the body tries to lower them by releasing large amounts of insulin. However, often too much insulin is released and this then forces the blood sugar levels to fall too far. In response the body stimulates the appetite of the individual in order to provide more glucose to raise levels. If more refined carbohydrates are consumed at this point, the cycle repeats and blood glucose levels rise and fall like a yoyo.
The fluctuations associated with consumption of refined carbohydrates can have a significant effect on mood. As blood sugar levels rise, energy levels also rise. It has been demonstrated that consumption of refined carbohydrates can lead to excitement and euphoria. High intakes of sugar can cause neurochemical changes in the brain. One of these changes is an increase in the production and release of the neurotransmitter dopamine and another can be an increase in the stimulation of opioid receptors. This response to sugar is similar to the response seen when addictive drugs are taken, and this explains the evidence that highly refined carbohydrate foods cause addiction in animals and humans. Such neurochemical changes have been termed ‘sugar dependence’ when they occur in experimental rats. This addictive property explains why those individuals under stress often turn to refined carbohydrate foods when they are under stress. Such neurochemical changes do not occur when unrefined carbohydrates are consumed.
Poor glycaemic control may be a significant factor in the development of detrimental mood changes. Evidence suggests that high and low blood sugar can cause a number of mood changes including depression and anxiety.
Low blood sugar levels may also lead to detrimental changes to mood. As blood levels fall, the body responds with a number of hormonal changes that are aimed at increasing blood sugar levels and stabilising energy levels. One of these changes is the release of adrenaline. Evidence suggests that elevated levels of adrenaline are associated with anxiety, and may be a causative factor in the development of anxious behaviour. Certainly the symptoms of panic attacks, a severe form of anxiety, are very similar to the symptoms experienced when adrenaline is released. The release of adrenaline that can occurs with low blood sugar levels is associated with anger, frustration and aggression. Low blood sugar levels are also associated with lethargy and apathy and can even induce stupor and sleep. This explains the cycle of manic behaviour often seen in those with poor glycaemic control. As blood sugar levels rise, euphoria develops, only to be replaced with a tiredness and exhaustion as blood sugar levels once again fall.
If the Western diet is consumed chronically, insulin resistance can develop. Insulin resistance is a condition that desensitises the insulin receptor to the actions of insulin, and this causes insulin to lose the ability to lower blood glucose levels. As a result blood sugar levels tend to remain elevated above their normal physiological levels, and insulin levels can also become elevated in response to this. Such chronically elevated levels of glucose are associated with detrimental changes to mood including depression. A number of studies have investigated the association between the elevated levels of blood sugar seen in those with type 1 and type 2 diabetes and depression. Generally, findings of such studies show that depression is associated with hyperglycaemia in patients with diabetes. In addition, studies also suggest that hyperglycemia in patients with diabetes is associated with anxiety. Chronically elevated levels of blood sugar may therefore have a significant detrimental effect on mood.
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