Each morning, after a strict overnight fast, Paula Wolfert drinks a cup-and-a-half of hot water with lemon, followed by a “bulletproof coffee” made from unsalted butter and coconut oil. At 11am, she makes her “gritty drink” – a sludge of greens, nuts, avocado and kefir. Finally, for lunch, she eats something like oven-steamed fish and vegetables. Wolfert eats no bread and hasn’t had a dessert in years.

Strangely enough, there’s nothing so unusual now about how Wolfert eats. Plenty of twentysomething wellness gurus follow a similar regime, all turmeric shots and energy balls. The difference is that Wolfert is 78 and an American cookbook author famous for her books on Morocco. She was once the queen of rich, meaty tagines and couscous. As she told the BBC Radio 4 Food Programme (in an award-winning episode, Diet and Dementia), Wolfert sacrificed the food she loved when she was diagnosed with dementia in 2012, because she wanted to do anything she could to stop her condition getting worse. As her memory palpably declined, food seemed like one of the few variables she could control. Wolfert feels that following her strict regime has slowed the onset of her dementia symptoms and made her “incredibly healthy”.

Is food medicine? The question has never been so current or so contentious. It’s clearly true that certain patterns of eating can sicken us and unfortunately, these are the patterns of eating that most people in developed countries now follow: low in vegetables and high in sugar, salt, refined oils and carbohydrates. Diet-related ill health, including heart disease and type 2 diabetes, now causes more deaths worldwide than tobacco. Some, therefore, conclude that there must be some specific and magical foods – quinoa! Goji berries! – that might offer an outright antidote to whatever it is that ails us. Many of the loudest of these voices are quacks or charlatans, or both. There are dark corners of the internet promising that the right diet can cure autism or offer something close to eternal life, coupled with fabulous skin. Some of this woo is exposed in the new book The Angry Chef: Bad Science and the Truth about Healthy Eating by Anthony Warner. The Angry Chef points out that many “health-giving” diets are anything but, leading to dangerously restrictive regimes that can easily tip over into eating disorders, especially for vulnerable young people.

But it would be wrong to dismiss the idea that food and health are connected, just because of a few – OK, a lot – of the claims are bogus. At this year’s Oxford Food Symposium, Canadian hospital chef Joshna Maharaj talked about the craziness of hospitals acting as if there is no connection between a patient’s health and what he or she eats. “Nourishment has long since been abandoned,” Maharaj said. In 2011, she took over the catering for a Toronto hospital and was appalled to find that the kitchen used almost no fresh produce and did not even have a fridge in which to store vegetables. Sick people were served meatloaf so processed and oily that Maharaj “could not find the adjectives” to describe it. She retrained the chefs, found local suppliers and made the radical decision to serve wholesome, appetising food for every meal, such as vibrant dals, soothing congee and sweet, roasted beetroot. It was no surprise to her that patient morale and health substantially improved with the new menus.

The average UK hospital still pays little attention to the powerful link between food and health. I’ve spoken to doctors who lament the irony of treating cardiac patients, only to see them heading to the hospital cafe to buy exactly the same fried and sugared junk foods that landed them on the ward in the first place. The health service spends a fortune on nutritional supplements (more than £300m in 2012), many of which could be avoided with better meals.

There are signs that many of us are sick of a medical system in which drugs are used – and not very effectively – to alleviate the symptoms of a bad diet. Wouldn’t it be better to try a way of eating that reduced your chances of getting ill in the first place? Market researchers have identified a trend for pill fatigue among consumers. Many would rather eat things such as yoghurt, green vegetables and nuts as a delicious preventative “medicine”, rather than be forced to swallow drugs as a palliative. Professor Roy Taylor at Newcastle University is among those suggesting that unlike medication, diet can actually reverse the effects on the body of type 2 diabetes.

Food is not a “patentable drug”, as Sheila Dillon observed on her radio programme about Paula Wolfert. But as the ancient Greek philosopher and physician Galen wrote in the second century AD: other remedies may be used for this or that, but without food it is “impossible to live either in health or in sickness”.

• Bee Wilson is a food journalist and author. Her latest book is First Bite: How We Learn to Eat