Washington- It has now been more than 96 hours since Indian Prime Minister Narendra Modi has had a morsel of food, Indian media reported today.

He has been subsisting only on hot water, not even lemon juice he was initially reported to be drinking. This is about the time experts say the process of ketosis sets in. The body starts to break down ketones from fatty tissues to use as fuel, instead of the usual glucose from the carbs we consume.

There was a time when ketosis was considered a critical response to fasting, but more recently researchers have said that depending on the individual, the body is resilient enough to subsist on little or nothing, perhaps up to three weeks in cases of water fasting. In fact, in recent years, many low-carb, high protein dieters go on such burn-the-fat binge-fasting — also known as muscle sparing — to lose weight.

What is less well chronicled is the effect of such fasting on the functioning of the mind. As anyone who has skipped a meal or two in a day can attest, an empty stomach is not the best friend of cool head or clear thinking. Typically, those who undertake fasts go into a low metabolic state, avoiding vigorous activity and quietly settling into a restful state.

Narendra Modi is not only doing that, but he has also embarked on a rigorous, almost tear-away schedule in the US that can burn-out a younger, fitter man chowing down good, healthy, regular meals. And he's doing that after a jetlag-inducing journey that long-distance flight veterans can tell you fatigues the mind.

Some 36 meetings and events in five days is what was on the original schedule, including energy sapping public rallies like the one in Central Park and Madison Square Garden over the weekend. That did not account for numerous unscheduled meetings. On Saturday, for instance, New Jersey governor Chris Christie dropped by at the hotel, for an unscheduled meeting that lasted over half an hour. Then there were school friends from Mehsana district, Gujarat.

How the Prime Minister is pulling it off this feat and the physiology involved is something that deserves to be studied regardless of one's personal pathology towards him. These are not one-way meetings during which he just listens and nods. He engages. Governor Christie and he exchanged notes about disaster management. Mayor Blasio and he discussed crowd control (with Modi telling about Kumbh Mela). With is Gujarati friends, he laughed and joked while posing for photographs. In one half-hour meeting, he wasn't even seen sipping the water in front of him.

Naturally, there is quite a bit of skepticism about whether he is totally off all kinds of food. What about a few Snickers bars at the bottom of his suitcase, joked one American businessman. But aides and officials around him swear they have not seen him have a single bite. One official who has seen him at close quarters for long said he was not surprised. "He has done it for nearly 40 years. Besides, women in India do this all the time. What's the big deal?" he asked.

But with this kind of schedule and intense engagement at the UN general assembly, Modi delivered his speech in a voice that was strong and resonant. Ditto Central Park, where he spoke in English, exhibiting impressive clarity and timbre. And the top item on his agenda, the meeting with President Obama, his cabinet members, and US lawmakers is still more than 24 hours away - in Washington DC. By that time, he’s been on a water diet for five days.