Practitioners and professionals of Yoga claims that practice of Yoga improves the digestive functions. How can it be measured whether the digestion improved or not?
But from a scientific point of view, it first needs to be clarified, that an experiment never can "prove" a theory. Experiments are only able to say, that (in this case) the opposite is unlikely...: It is unlikely that Yoga does not improve digestive functions, however this is not precise, I think it gives you a gist.
And the way it is done is:
Define a "Manipulation" or "independent variable": for example invite two groups of people: one group makes yoga for half an hour in your laboratory, the other group only sits there for the same amount of time. Make sure, that "doing Yoga" is the only difference between what is happening in both groups.
Define "improving digestive function" - this is your dependent variable. I do not have a clue, what this could be: maybe the quality of the stool. Whatever it is, it should be a plausible indicator of the quality of digestive functions. Maybe we have some physicians here :)
Now you can do diffrent things.
1. Forget the groups, but analyse the stool before doing yoga and after doing yoga. In terms of quality there should be an improvement...
2. Invite those two groups, and analyse the stool only afterwards. There should be a difference then, to "reject" the hypothesis, that yoga does not improve the digestives....
3. Do both.
Make sure, that no one you invite to participate does actually yoga for herself regularly. The idea of testing is to have the highest possible control for causal effects. Namely, your manipulation is the only systematic source of possible differences in the digestive functions. So think about other explanations too, and rule them out.
The improved digestive function will also reflect on the general health of the person.So dietary intake ,intellect ,immunity all will be affected in a positive way.So.it will be interesting to judge the improvement with a fixed parameter.I Think BMI/Immunity should be judged rather than digestion.
A good model to use is the 300+ studies done with Transcendental Meditation. In a given study, two matched groups were used to track improvement (or not) for a dazzling variety of conditions: high blood pressure/circulatory efficiency, AIDS, immune responsiveness, emotional stability, academic improvement, loads more. If you go to the TM site, you'll be linked to papers that outline the methodology involved. It may give you ideas how to set up the experiment models.
In lieu of stool samples, I'd have subjects fill out a questionnaire that addresses their description of stool, along with variables like indigestion, acid reflux, hunger (less hunger means more efficient digestion), transit time of food from eating meals to elimination, even food cravings.
I agree with Jyoti that perhaps immunity would be an easier thing to evaluate. However, you could also assess people's outlook on life.
Go to the TM site and read some of the studies. That's the best model I can think of.
Sir, Dr Prakash C. Malshe in haridwar can help you a lot. He is an allopathic physician, worked on yoga along with modern diagnostic tools. He has written a book on this - "A medical understanding of yoga".
His contact details- 1073 Gayatrilok Apartmants, Delhi Road, Kankhal,Haridwar, India 249408 mobile no.094120 73252
Self-regulation evaluation of therapeutic yoga and walking for patients with irritable bowel syndrome: a pilot study.hahabi L, Naliboff BD, Shapiro D.Psychol Health Med. 2015 Jun 18:1-13.