Hull and East Yorkshire Hospitals NHS Trust, Institute of Rehabilitation, 215 Anlaby Road, Hull HU3 2PG and
1 Division of Psychiatry, Kent Institute of Medicine and Health Sciences, University of Kent at Canterbury, Canterbury, Kent CT2 7PD, UK
Received 12 January 1999; in revised form 18 March 1999; accepted 25 April 1999
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ABSTRACT |
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INTRODUCTION |
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Although brain metabolism can be altered by amino acid supplementation, these changes may also be achieved by dietary manipulation (Young, 1991). This approach can be explored by modulating the proportions of carbohydrates and proteins in the diet (Wurtman and Wurtman, 1995
). The rationale for this is that a high carbohydrate meal will induce an insulin surge resulting in LNAA being incorporated into muscle protein, thus elevating the tryptophan/LNAA ratio (Markus et al., 1998
).
Depression and anxiety states have long been recognized as co-morbid and co-presenting features of alcohol dependency (Allan, 1995; Brown et al., 1995
). Therefore, the consequence of tryptophan manipulation increasing 5-HT and reducing anxiety and depression may be of potential therapeutic efficacy in appropriately motivated individuals (Møller, 1992
) and therefore appropriately motivated patients with alcohol dependence. The aim of the present pilot study was to determine whether manipulation of tryptophan by diet alone significantly influences self-report affective status of alcohol-dependent subjects.
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SUBJECTS AND METHODS |
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Experimental design and statistics
The study used a counterbalanced, repeated measures design in which high carbohydrate (CAR), high protein (PRO) and nutritionally balanced (NUT) breakfasts were supplied to subjects on three separate days. Blood samples were collected (at 08:30) before breakfast, which was taken at 09:00, and 2.5 h after each breakfast (i.e. at 11:30). Self-report measures of affective state were then administered to the subjects. The independent variable was diet type (CAR/PRO/NUT). The psychological dependent variables were sum scores on a battery of self-report affective state measures. The biochemical component, the nutritionally balanced breakfast, consisted of: cereal with almonds/milk or a glass (200 ml) of semi-skimmed milk, fish (haddock), poached or boiled egg, non-fat cheese/soya food, and one piece of toast. The high carbohydrate meal consisted of cereal with almonds/milk or a glass (200 ml) of semi-skimmed milk, and two slices of bread. The high protein meal consisted of haddock/poached or boiled egg/non-fat cheese/soya food, and one piece of toast. Coffee/tea was taken in all cases as normal. Statistical analysis was performed using one-way analysis of variance (ANOVA).
Biochemical analysis
The blood samples were collected via 9-ml Vacutainers (Becton Dickinson) and serum was separated by centrifugation at 3000 rpm for 10 min and the supernatant separated into Eppendorf tubes as follows: 200 µl of serum plus 200 µl of 5% (w/v) sulpho-salicylic acid, for amino acid analysis; 200 µl of serum and other aliquots set up for analysis of tryptophan metabolites and liver function tests. The samples were stored at 80°C until analysis. Amino acids were measured by the method of Teerlink et al. (1994).
Psychological measures
The psychological test battery comprised self-report measures that have been widely clinically evaluated and have established psychometric properties (Martin and Thompson, 2000). The following instruments were used: (1) Hospital Anxiety and Depression (HAD) scale (Zigmond and Snaith, 1983
); (2) Beck Depression Inventory (BDI; Beck et al., 1961); (3) Spielberger StateTrait Anxiety Inventory (STAI; Spielberger et al., 1983); (4) Locus of Control of Behaviour (LCB) scale (Craig et al., 1984
).
After giving the blood sample at 11:30, subjects were asked to complete the self-report questionnaires at 11:35. This procedure was repeated on days 2 and 3 when the subjects were assigned (crossed over) to the alternative meals (CAR/ PRO/NUT).
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RESULTS |
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DISCUSSION |
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These results are therefore disappointing, since they suggest that a biological basis for improving mood via conscientious dietary choice, and without the use of prescribed pharmacotherapy, is unsupported. Alternatively, the relatively small sample size in this pilot study may be a fundamental limitation in terms of the lack of dietary effects observed on either the biological or psychological measures used. Power estimations revealed that, in a larger subject population of marginally more than 300 subjects, a significant effect of dietary manipulation is likely to be observed on all the self-report affective measures.
However, relating any observed dietary effect on mood status to biological substrates in a larger replication study would be problematic in view of the incomplete state of knowledge regarding tryptophan metabolism, and there would be little clinical significance of a result that required such a large sample to demonstrate.
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ACKNOWLEDGEMENTS |
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FOOTNOTES |
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REFERENCES |
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