What's a White House dinner without dinner? Modi and Obama will find out.

How do you serve dinner to a head of state who won't eat? The White House will attempt to answer that tonight, as President Obama hosts the fasting Indian Prime Minister Narendra Modi for a private dinner. 

Unlike most of his predecessors in India's highest political office, Mr. Modi, who took office in May, is a devout Hindu. He is fasting for the Hindu religious festival of Navratri, a practice he's maintained for the past 40 years.

The leader – who was banned from traveling to the United States for nearly a decade because of questions over his actions during deadly Hindu-Muslim riots in 2002 – is enjoying a so-far triumphal first official visit, including giving his first speech at the United Nations, and headlining a sold-out event at Madison Square Garden over the weekend.

Even more than the test of etiquette at the White House dinner tonight will be the test of ties between Mr. Obama and Modi, who are looking to reinvigorate US-India relations after a frosty year, including a diplomatic spat over an Indian consular officer who was arrested and strip-searched in New York, angering many Indians.

Back home in India, Modi's choice to observe his regular practice despite the major diplomatic engagement is making headlines, with the Times of India noting that "Modi's fast ... baffles Americans." The paper praised Modi for "pulling off" the fast while holding 36 meetings and events in five days. "These are not one-way meetings during which he just listens and nods. He engages," the paper wrote. 

What is the Navratri festival? 

Navratri is a nine-day festival, during which Indian Hindus worship the mother goddess Durga. Navratri, derived from the ancient Sanskrit words "nine nights," is celebrated twice a year, once to mark the start of summer and again to announce the onset of winter. This year the festival falls from Sept. 25 to Oct. 3.

During the festival, Hindus fast, pray, and dance to please the mother goddess. The festival is considered auspicious and many people purchases cars, jewelry, and buy houses. The festival culminates on the 10th day, known as Dussehra, which marks the victory of good over evil and is often celebrated with fireworks and reenactments of ancient Hindu stories.

The festival is practiced differently depending on the region. Many devotees restrict their diet to fruit and vegetables and give up meat, onions, and garlic. Others, like Modi, who is a strict vegetarian, do not eat at all. 

Modi has cultivated a formidable reputation for strict self-discipline. He reportedly sleeps for only five hours – sometimes even less. Journalists say that he wakes up at 5 a.m., meditates, prays, and logs on to the Internet to check what is written about him.

His icon is philosopher-monk Swami Vivekanand, who championed yoga and meditation to the Western world in the 19th century. 

After he left home as a young man, Modi found inspiration from his writings and become a campaigner for Rashtriya Swayamsevak Sangh (RSS), a right-wing Hindu organization that aims to make India a Hindu nation and functions as an ideological fountainhead to a host of right-wing Hindu groups.

Warming ties?

The White House visit is part of a warming of ties between official Washington and Modi, who had been denied a US visa since 2005 for his role in riots between Hindus and Muslims that killed over 1,000 under his watch as chief minister in Gujarat, India. A court cleared Modi of responsibility, though his critics maintain that he could have done more to stop the violence. 

Officials at India’s foreign office say that the White House had been informed of Modi's dietary requirements. When asked about Mr. Modi’s plans to fast, India’s Foreign Ministry spokesman Syed Akbaruddin said it was “normal diplomatic practice to indicate the dietary preferences of the guests to the hosts” ahead of a foreign visit.

“They have taken note of it and have prepared everything accordingly,” Mr. Akbaruddin told the Indian news agency PTI.