Acupuncture treatment can affect appetite, intestinal motility, and metabolism, as well as emotional factors such as stress.

Increases in neural activity in the ventromedial nuclei (most commonly associated with satiety) of the hypothalamus, in tone in the smooth muscle of the stomach and in levels of enkephalin, beta-endorphin, and serotonin in plasma and brain tissue have also been observed with the application of acupuncture.

It has been observed that acupuncture in obese people increases excitability of the satiety center in the ventromedial nuclei of the hypothalamus.

Acupuncture stimulates the auricular branch of the vagal nerve and raises serotonin levels.
Both of these activities have been shown to increase tone in the smooth muscle of the stomach, thus suppressing appetite.

Among other things, serotonin enhances intestinal motility. It also controls stress and depression via endorphin and dopamine production.

In addition to these effects, it is thought that the increase in plasma levels of beta-endorphin after acupuncture application can contribute to the body weight loss in obese people by mobilizing the body energy depots through lipolithic effect.

References:
1. Cabýoglu MT, Ergene N, Tan U. The treatment of obesity by acupuncture. Int J Neurosci. 2006 Feb;116(2):165-75. PMID: 16393882.
2. Image by nicneven.