Jupiter is the significator of fortune, happiness and abundance. Sixth House is the significator of debts, diseases and enemies. Naturally Sixth House isn't the best placement for Jupiter. Ofcourse his aspects provide boost for Career and Savings. Still in a Dushamsthana placement the planet of fortune loses most of his strength. 

      Jupiter is a planet associated with obesity and laziness. There are high chances of native becoming slow and obese unless he exercises regularly or unless there are planets like Saturn, Mars, Sun or Ketu in Ascendant or co-tenants with Jupiter. That is not to say it is curse to have Jupiter in Sixth House. Jupiter gives positive results even in negative conditions. Sixth House rules over service and native is employed as a lecturer or as a consultant. If other stars favor then he could be working as a Political Advisor or even as a Diplomat. Career is generally stable unless other factors influence Career House. Also native maybe able to have good Savings. Investments in Gold is also favorable via aspect on Second House. Aspect on Twelfth House may create a foreign traveller or one who has to settle abroad to make a living. But it may not always be the case. Aspect on Twelfth House could also lead a person to try ascetic lifestyle and live in a monestary(ashram). 

     According to B. V. Raman: "Jupiter in Sixth House gives a person humiliation. He/She suffers from indigestion and flatulence. Native maybe over-indulgent and health suffers due to over-indulgence."

     Sixth House is definitely not the best place for Jupiter. But it is managable if some self-restrictions are imposed. Firstly the person must not eat fatty foods, red meat or diet with high sugar. Regular exercise especially Kapal Bhati Pranayam, Bahya Pranayam and Surya Namaskar are essential. There are other yoga postures which also help control fat which can be looked up on internet. Native must make a habit of drinking Bottle Gourd Juice(Lauki Juice) or in Western Countries it can be Spinach Juice. Native should regularly consume Yellow Lentils(Tuvar Dal) along with Bottle Gourd(Lauki) to stay healthy and fit. Last but not the least they should pray to Lord Vishnu if they suffer from very bad fortune.