Impact of fatty acids on brain circulation, structure and function
Introduction
Paleontological studies have shown that feeding habits played a crucial role in the development of the human brain [1]. Differences in diet among primates affected survival rate and the ability to reproduce, which are both related to brain size and cognitive functioning [2]. It is now known that brain size increased with the development of skills that required proper cognition, such as cooking and access to food and this led to the formation of the modern brain as we know now [3]. An evident example of diet effects on the brain was observed when comparing encephalisation (increasing brain/body-mass ratio) of hominids (early humans) living close to the shore with that of hominids living in-land [4]. A shore-based diet, which included high consumption of fish, led to extensive encephalisation in this population. This is probably related to the higher consumption of omega-3 fatty acids like docosahexaenoic acid (DHA; 22:6n−3) in this shore-based diet, as DHA is an important brain constituent present in cell membranes but cannot be synthesized efficiently by the human body itself.
When we analyze the situation now-a-days, a similar comparison can be made: with on one side a ‘Mediterranean-type diet’ and on the other side a ‘Western-type diet’. The conception of a Mediterranean-type diet (which is rich in long-chain polyunsaturated fatty acids) is derived from the combination of high intake of fruits, vegetables, nuts, cereals, olives and olive oil and more fish; less milk but more cheese; less meat; and moderate amounts of wine [5]. On the other hand, a Western-type diet is the result of increased saturated and trans fatty acids consumption due to introduction of food staples and food-processing procedures after the Industrial Revolution [6]. This difference in diet is reflected in an increased death rate caused by cancer and heart disease in the United States compared to Crete, which are characterized by consuming a Western-type diet and Mediterranean-type diet, respectively [7]. Outcome of cancer and heart disease is clearly affected by different diets and their effect on the cardiovascular system [8]. Cardiovascular risk factors are considered important risk factors for the onset of neurological diseases such as stroke and Alzheimer′s Disease (AD). The focus of this review will be on the effects of dietary components on the brain as there is abundant data available revealing the effects of specific diet components on brain health and mental functioning [9]. For example, high serum cholesterol levels, possibly via dietary intake of high saturated fat, in midlife increases the risk of AD in later life while a diet low in saturated fat like the Mediterranean diet is inversely related to this [10], [11]. Several groups tested the possibilities to slow down the progression of diseases like AD with nutrition-based intervention in animals and humans. Experimental data revealing the influence of diet components on three important indicators of brain health: (1) circulation, (2) structure and (3) function, will be highlighted in the present review. In this context, we will mainly emphasize the effects of omega-3 long-chain polyunsaturated fatty acids (ω3-LCPUFAs) on these aspects and compare this with the evidence found concerning the intake of saturated fatty acids. Obtaining more knowledge concerning the aftermaths of malnutrition on the brain is necessary since diseases like obesity, metabolic syndrome and diabetes gain prevalence in modern society.
Section snippets
Circulation
Due to high demands of energy by the brain and its low capacity to store this energy, the brain is the most highly perfused part of the human body [12]. Proper functioning, including adequate cerebral blood flow (CBF) and vessel reactivity, is necessary to ensure the microenvironment in which brain cells function efficiently. The importance of proper cerebral circulation is reflected in cerebrovascular and neurodegenerative diseases such as atherosclerosis, stroke and AD. Higher cerebral
Structure
The hypothesis that diet-induced changes on cerebral circulation may be linked to changes in brain structure is strengthened by a recent study of Chen et al. (2013). They showed a significant relationship between cortical CBF (using arterial spin labeling) and subcortical white-matter integrity (assessed by diffusion tensor imaging; DTI) in healthy human participants [51]. Since diet clearly affects cerebral blood flow based on the data reviewed earlier, potential diet effects are also expected
Function
Cognitive decline is a widely accepted phenomenon associated with normative aging and presumably caused by structural changes in the brain. Structural impairment of the brain, and especially white matter loss and dis-integrity, is significantly associated with poor brain functioning (i.e. cognitive performance). High FA values, and thus proper (white matter) connectivity between brain regions, are most often correlated with high levels of task performance [83], [84], [85], [86]. However, in
Conclusion
The awareness of food necessity has evolved from the simple means of providing energy and building material to the body into a potential therapeutic mediator to prevent and protect the body against the onset and progression of diseases. An increasing amount of studies demonstrated the beneficial and detrimental effects of distinct dietary components on the healthy and diseased brain. Within this framework, this review highlights important data regarding the effects of ω3-LCPUFAs and saturated
Acknowledgments
The research leading to these results has received funding from the European Community′s Seventh Framework Programme (FP7/2007-2013) under Grant agreement no. 211696.
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