Looking for a book that I read in the 80's, so 30-39 years ago. It was science fiction or possibly fantasy. A man was looking to lose weight. He taps into something primal through some experiments and meditation. He did lose weight, but also experienced other changes. He became stronger, faster, and more aggressive. Possible but uncertain details were there being a friend helping or running the experiment as well as a girlfriend. Also, there was a scene about him fighting a master with fighting sticks. This was English and as I was reading the Tor edition Conan novels it is likely this was adult fiction as well. Unfortunately this everything I can recall, and some of these details are a bit fuzzy.
Almost certainly The Kundalini Equation by Steven Barnes, published in 1986. It has the hero, Adam Ludlum, trying to lose weight and become fit, finding a manuscript that details a system of meditation and visualization that allows him to tap into some primal energy. He becomes stronger, faster and instinctively duplicate different martial arts. There is the stick fighting martial artist and his growing aggression.
There is a nice essay from the author about writing it here.