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As an obese individual adopts a healthy diet and exercise regime, what happens within the body?

When the obese individual adopts a healthy lifestyle, there are certain physical and biological consequences that occur with the reduction of dietary fat. There are a number of different types of dietary fat.

These are broadly speaking, triglycerides and sterols, with triglycerides being sub-classed as saturated, mono unsaturated and polyunsaturated fats. Dieticians advise that obese individuals need to regulate and monitor the amount of saturated fats they consume. The discussion below will focus on how the role of which cholesterol (a saturated fat) plays in psychological functioning and the psychological consequences of reducing dietary intake of fat.

Cholesterol has a vital biological function, in that it is an integral part of the structure of cell walls - i.e. the lipid bilayer. The structure of the cell membrane allows molecules to pass through, via the protein channel. This is the mechanism whereby neurotransmitters cross the synaptic cleft. Changes in the ability of the cell wall to allow molecules of various sizes to enter and leave will affect neural function. Evidence suggests that alterations in the dietary intake of cholesterol can alter psychological functioning.

Morgan et al (1993) found that older adults with low cholesterol levels had an increased score on the Beck Depression Inventory. Therefore, this suggests lowering the intake of cholesterol may heighten the susceptibility of depression. However, this has been disputed by van Doornen and Orlebeke, (1982) who have found that high levels of cholesterol was associated with increased depression. However, it must be noted that these are cross sectional studies, examine the relationship between cholesterol levels and depression at a single point in time - therefore, the two studies can not be accurately relied upon as a measure of depression - as depressive illnesses can vary between individuals and for the individual themselves.

However, one way to unravel this discrepancy is to examine the results of studies which have attempted to lower fat levels by pharmacological or dietary means. For example, Glueck et al (1993) showed that lowering the blood triglyceride levels (and therefore raising the concentration of cholesterol) by means of a drug called RX reduced depressive symptoms, as measured by the Beck Depression Inventory.

Therefore, what is the relationship between cholesterol and feelings of depression?

Engelberg (1992) suggests that the effects of lowering cholesterol levels by dietary means will affect the serotonergic functioning in the brain. Engelberg purposed that reducing cholesterol in the brain, which will alter the cell membrane fluidity of the central nervous system and decrease the exposure of serotonin receptors on the surface of the neuronal cell membrane. This would then lead to the poor uptake of serotonin from the blood and a resultant decrease in serotonin entry into the brain.

However, there has been very little evidence to support Engelberg's (1992) notion. This may be explained by the widely accepted believe that serotonin is essential for the regulate of mood, sleep, temperament and endocrine Furthermore, Serotonin has been noted to produce an inhibitory effect on the nervous system that calms, soothes and generates feelings of general contentment and satiation.

A reason for the relief in depressive symptoms for individuals, who adopt a healthier lifestyle than before, may be contributed to the likelihood of a new exercise regime. Studies have shown that serotonin levels are raised with increased activity and the production of serotonin is increased for some days after the activity. This can be explained by the increased activation of the brain chemical - endorphins, caused by the serotonin system. This has been proven by participates with recorded heightened levels of endorphins present in the blood stream during and after exercise (Moore, 1982).

Endorphins, has been found to be very similar to morphine in chemical structure and pain killing abilities. Therefore, endorphins act as a pain reducer and are released when the body is in stress. Furthermore, exercise is thought to have psychological benefits as well as weigh loss. Exercise causes a boost in self esteem, an improved self-image, confidence and feelings of accomplishment as well as a break from the other aspects of life. However, the mere presence of the chemical does not prove that it is the main factor in causing this elation. There is some argument that maintains it is serotonin, not endorphins that is responsible for these feel good factor after exercise. The reason for this being, that the endorphins don't leave the bloodstream.

Therefore do not stimulate the receptors in the brain to stimulate these good emotions. Furthermore, serotonin is often said to causes a suppression of appetite. However, there has not been much research done on the role of serotonin in the exercise process (see Dey, 1994 for an exception).

In light of the above evidence, it is fair to say that when an obese individual adopts a healthy diet and exercise regime, there are certain psychological alterations within the body. This may be a consequence of the individual adopting an exercise regime, which may encourage the release of endorphins and feel good hormones. Furthermore, the increase in good mood may be attributed to the fact that when exercising, the body also activates the serotonin levels within the brain (which is believed to activate the increased activity of endorphins as well).

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Conclusion

Yet from the evidence discussed above, it is unsure which brain chemical is responsible for the reduction in depressive symptoms - endorphins or serotonin. However, referring to the discussion above concerning cholesterol levels, this can add support to the claim, that changes in serotonin levels are responsible for the psychological differences within the individual. However, this then possess the question as to whether it is lowering the intake of saturated fats (cholesterol) encourages the increased activity of serotonin, or is it exercise?

It may be that exercise encourages the individual to eat healthier, more nutritious food e.g. banana's which are believed to encourage the release of serotonin, because the body is craving a top up of the psychological benefits of its receiving.

References

Dey, S (1994). Physical exercise as a novel antidepressant agent: possible role of serotonin receptor subtypes. Physiological Behaviour 55(2):323-9.

Engelberg, H, "Low serum cholesterol and suicide" Lancet 1992 pp. 727-729

Glueck, C.J., Tieger, M., Kunkel, R., Tracy, T., Speirs, J., Streicher, P., and Illig, E (1993). Improvements in symptoms of depression in an index of life stressors accompany treatment of severe hypertriglyceridemia. Biological Psychiatry, 34, 240-252

Moore, M. (1982). Endorphins and exercise: a puzzling relationship. Physician Sports Med, 10 (2), 111-114.

Morgan, RE, "Plasma cholesterol and depressive symptoms in older men" Lancet 1993 pp. 75-79

van Doornen LJP, Orlebeke KF. (1982). Stress, personality and serum cholesterol level. Journal of Human Stress; 8:24-29.

Pinel, John P.J. (2000) Biopsychology. (4th Ed). Boston: Allyn and Bacon.

Wardle, J., Rogers, P.J., Judd, P., Taylor, M.A., Rapoport, L., Green, M and Nicholson-Perry, K. (2000) Randomised trails of the effects of cholesterol-lowering dietary treatment on psychological functioning. American Journal of Medicine, 108, 547-553

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