Discussions and conclusion

Yoga is a state (meaning union) which is defined as a high level of consciousness achieved through a fully rested relaxed body and a fully awake and relaxed mind [5]. The effect of yoga on body function may be related to decreased arousal or a decrease in sympathetic nervous system activity. Meditation or relaxation according to yogic scriptures is a calming of the mind, slowing of the breath and relaxation of the muscles [1-3], and this is consistent with the effect of small changes in the psychological state on heart rate, respiratory rate and energy expenditure [6,8]. Earlier studies have demonstrated that transcendental meditation, Zen meditation, Yogic medita- tion and certain pranayama and relaxation techniques reduce O2 consumption, CO2 elimination, metabolic rate, heart rate, pulse rate, breath rate measured immediately prior to, during and after the meditation or relaxation techniques [15-18,5,6]. Recordings of the EEG in subjects practicing transcendental meditation have also demon- strated a predominant alpha wave activity (even with eyes half open) which progressively increased in amplitude and decreased in frequency during the first stage of tran- scendental meditation, followed by occasional theta waves in the second stage of meditation [19]. While the voluntary cessation of the heart beat by a yogi has been recorded [20], yogic and Zen meditators could also reduce their oxygen consumption, metabolic rate, and heart rate for short periods of time by [21,16]. These acute studies suggest that the mechanism by which this may occur is a possible alteration of autonomic nervous function, and studies showing decreased arousal with yoga [22,18] support this view.
The reduction in BMR in long term yoga practitioners might be considered to be a form of adaptation through reduced arousal in healthy, well nourished men and women, which, while similar in direction, is probably dif- ferent from the adaptation to chronic undernutrition [23,24]. The importance of the present study is that it sought to evaluate real life practice of yoga, which usually combines several techniques and is practiced over a period of time. It also suggests a hierarchy of effects, such that the predominant outcome with mixed yoga practice (using techniques that have a stimulatory or inhibitory

effect) is one of inhibition. The difference in BMR (adjusted for body weight) was much greater for the women rather than men in this study. It is possible the yoga training was more effective in women or that women respond differently to the practice of yoga, since women can respond differently to different levels of stress [25,26]. This is not unreasonable, and certainly needs further investigation. One drawback in the present study was that the phase of the menstrual cycle of the women was not constant during the measurement period, nor was a detailed menstrual history obtained. The present study also did not measure body composition, and it is possible that the differences in BMR may disappear after correcting for body composition differences. It is difficult to ascribe a direct mechanism related to yoga through physiological means, since these were not measured. The interesting fol- low up to these studies is to observe how long these changes last after the cessation of yoga practice, and whether the continued practice of such a lifestyle would bring certain changes that are more persistent in nature at the cellular level. There were no large differences in RQ between the groups; although there was a small but signif- icant difference between yoga and non yoga groups in the RQ, this was different in direction between men and women, and in general, the rounded off value of the RQ in all groups was 0.9. This is consistent with a high carbo- hydrate intake population, as has been shown earlier [27] and does not explain the difference between groups.
The BMR can also adapt to the nutritional status and phys- ical activity of the individual. Metabolic adaptations in terms of a reduced BMR are known to occur in acute [24] and chronic [28,23] undernutrition. The subjects in the present study were normally nourished and did not report any acute weight change during the last six months, and the women were non-pregnant and non-lactating. Physical activity is also known to influence the BMR, for exam- ple, endurance trained athletes have been shown to have a higher BMR [29] and high intensity exercise on the pre- vious day has been shown to increase the BMR [30], although low and moderate intensity exercises does not seem to have a similar effect [31]. Notwithstanding the latter finding, it would seem likely that yoga, which is a mild to moderate form of activity [10,11], would, if at all, increase the BMR. However, this study shows that yoga, when practiced in a combined mode, with asana, pra- nayama and meditation over a period of time, actually reduces the BMR. Other respiratory parameters such as minute ventilation volume and breath flow rate also were lower in the yoga group suggesting a controlled pattern of breathing. Both groups of subjects had similar resting heart rates suggesting that there was no actual change in physical fitness between the groups.
An interesting implication that underlies the reduced BMR with long term combined yoga practice is whether it creates a propensity for weight gain and fat deposition. The latter is a problem in India, in which higher adiposity is observed at a lower body mass index, and in general, urban prevalence of chronic non-communicable disease is high [32,33] In contrast, yoga is thought to be associ- ated with positive effects on health, and this might be related to other concomitant beneficial changes in appe- tite, food intake and body composition. The effect of a lowered BMR on the risk for chronic disease needs to be evaluated through follow up studies, with measurements of the effect of long term combined yoga on the appetite, weight stability, sense of well-being and body composi- tion. In conclusion, the present study demonstrates that the long term practice of yoga and meditation leads to a decline in the BMR, and this decline is seen in men and women.