A majority of visitors do fast, but at the clinic, that means eating 250 calories a day. A very low fat, very fresh and fully organic menu is offered. And some guests choose an 800- or 1,200-calorie diet over fasting.
Peter van der Lugt from Amsterdam sips his juice slowly in a salon with a sweeping view of the lake. He's on day four of a two-week fast.
"It's not that I've given up eating," he says. "But it's good to find out that you can do without for some time."
Critics say fasting can be dangerous. Clinic director Raymound Wilhelmi stresses that visitors at Buchinger are under medical supervision.
"Fasting is not a Sunday afternoon walk," he says. "It's not so easy as people say, 'Oh, I just will stop eating.' It's not that way, especially with people who have some illnesses, who are already, you know, not so young anymore and have some problems — not only physical problems but also psychological problems."
The clinic's chief doctor, Christian Kuhn, says fasting naturally leads people to focus inward and opens them to what he calls "spiritual nutrition" — what people really need, he says, to heal or change their lives.
"We have an approach that body, mind and spirit are an entity," Kuhn says. "And we don't work just with the body."
So the clinic offers psychotherapy, cultural evenings out, treatments from acupuncture to adding oxygen to the blood and relaxation classes reflecting a wide range of trends. Exercise is a big part of the program, especially because many people come just to lose weight.
Buchinger staff members say that fasting requires physical and mental stimulation in a place conducive to inner reflection to get what the clinic sees itself as selling: transformation. Anna van der Wee, heading home after a two-week fast, says the experience triggered a new level of clarity.
"It opens your mind," she says. "It gives you a sense of precision and sharpness and yet, at the same time, wideness. So it gives you a larger perspective on things. Maybe it's because [of] all the time you don't spend thinking about food."
Tarik Mohana, an Egyptian-born lawyer living in London, came mainly to detoxify his body.
"When you go through the process, you realize how unhealthy you are, and how healthy you become, and it's still possible to become," he says. "Every once in a while, it's good to just completely let your body detox, get everything out."
Mohana says all this while smoking a cigarette.
"Well, considering the fact that I smoke a pack a day, and here I'm down to four cigarettes a day, I think that's a remarkable achievement," he says.
Buchinger's guests are increasingly foreign and getting younger, and about two-thirds are repeat customers. In traditional health care, that might be considered failure, but at the clinic it's seen as evidence the treatment offers regular regeneration.
Fasting proponents claim that regularly stopping food can help a range of diseases, particularly chronic inflammations or intestinal problems. There are few peer-reviewed studies on fasting, although one published in the British medical journal The Lancet showed fasting followed by a controlled diet helped relieve rheumatoid arthritis.
For thousands of years, beginning with philosophers like Hippocrates, Socrates and Plato, fasting was recommended for health reasons. The Bible writes that Moses and Jesus fasted for 40 days for spiritual renewal.
To understand how the body reacts to a lack of food, you could start by looking at what happens to newborns. Newborns can't sleep through the night because they need to eat every few hours. They don't produce enough glycogen, the body's form of stored sugar, to make energy.
"Glycogen is necessary for thinking; it's necessary for muscle action; it's necessary just for the cells to live in general," says Dr. Naomi Neufeld, an endocrinologist.
Neufeld says most adults need about 2,000 calories a day. Those calories make energy, or glycogen. Neufeld says it doesn't hurt — it might even help the body — to fast or stop eating for short periods of time, say 24 hours once a week, as long as you drink water.
"You re-tune the body, suppress insulin secretion, reduce the taste for sugar, so sugar becomes something you're less fond of taking," Neufeld says.
Eventually the body burns up stored sugars, or glycogen, so less insulin is needed to help the body digest food. That gives the pancreas a rest. On juice diets recommended by some spas, you may lose weight, but your digestive system doesn't get that rest.