Looking at Jeannette Hyde today - tall, slim and radiating good health - it's hard to believe that 11 years ago she was in the grip of a breakdown that left her exhausted and barely able to function. "I woke up one morning and couldn't move my neck. The level of pain was off the scale. I couldn't sit, turn my head or drive," she remembers.

Working 12-hour days as a journalist on a national newspaper, Hyde was living off adrenalin and the odd croissant and coffee, wolfed down at her desk between interviews.

Yet today, looking around the kitchen in her beautiful Richmond, London, home that she shares with her husband, Markus, and children Hannah, 16, and Max, 13, there's not a French pastry in sight. And her eyes are sparkling. So what changed?

Hyde left her stressful job, studied nutrition at Westminster University, and discovered the ways in which our diets can not only change how our bodies look, but also how we feel and function. Countless clients, five years of clinical experience and mountains of research later, she is convinced that the key to health and weight loss lies not in our muscles or even in our minds, but in our guts.

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"Our intestines, especially our large intestines, contain masses of bacteria, weighing a kilo and a half - and these are instrumental to our wellbeing," says Hyde.

This "microbiome" of bacteria consists of 100 trillion bacterial cells, and scientists are now calling it the "forgotten organ".

Last year, as Hyde was completing her new book, The Gut Makeover - which outlines a four-week healthier-eating plan - she could barely keep up with the peer-reviewed papers being published that linked gut bacteria to yet another aspect of health, from mood to immunity, obesity to autism.

Just last month, researchers at the University of Iowa found that people's gut bacteria could determine the amount of calories they burned while sleeping; previous studies have found that people with unhealthy gut bacteria absorb more calories from the food they eat than those with healthy bacteria, as it can influence appetite hormones such as leptin and ghrelin.

After that morning crippled by neck pain, Hyde took a year off to regroup and spend time with her children, then aged 6 and 2. She was prescribed anti-inflammatories and anti-depressants, which made no difference whatsoever. A serial dieter since the age of 18, like so many of her generation (she's now 47), Hyde thought the key to a healthy body lay in a calorie-controlled diet.

"I've been on more diets than I care to remember. At 18, I bought a little yellow book listing calorie counts and became such an expert that I could calculate the calories in any meal without even looking at it."

Within a few months, her 1.7m frame went from a healthy 60kg to 51kg. "Then, one day, I woke up and suddenly had the most insatiable hunger of my life, and it went on for months. I just couldn't stop eating and craving junk foods such as McDonald's, which I had never eaten before. I would buy a loaf of sliced white bread and a pot of jam and sit by the toaster preparing and eating each slice until the entire loaf was gone." In six months, she gained 22kg.

Years of "misery-bingeing and crash-dieting", along with punishing exercise routines, followed before Hyde realised what she was doing to herself, and finally started eating more vegetables, more home-cooked meals, more live yoghurts, more fresh meat and fish. It was all prompted by her mother, who would constantly nag Hyde to "just eat properly".

Jeannette Hyde advocates eating the likes of spiralised butternut squash, rocket, artichokes and marrow with seasonal vegetables. Photo / Supplied
Jeannette Hyde advocates eating the likes of spiralised butternut squash, rocket, artichokes and marrow with seasonal vegetables. Photo / Supplied

"That was years before I began my personal crusade to find out the truth about food," remembers Hyde. "But seeing what is emerging about eating for a healthy microbiome, I realised that it's real food that holds the answer, because that is what stimulates the flourishing of as many different and varied species of gut bugs as possible. Only real, whole food - not a probiotic pill or drink - can deliver that long-term," she says.

Most of Hyde's clients are in the same place she was 11 years ago, pushing themselves hard at work, teetering on the brink of burnout while serially dieting and calorie-counting; perhaps not diagnosed with an eating disorder, but certainly disordered eaters.

"They're almost afraid to eat," says Hyde. "As a result, they're exhausted." They end up in Hyde's clinic complaining of vague symptoms, including irritable bowel syndrome (IBS), inability to lose weight, skin issues such as adult acne, eczema and psoriasis and, most commonly, chronic constipation. "Some people think going twice a week is normal. It's not. You need to be having at least one bowel movement a day, ideally more, and that should be solid, well-formed and pass easily, without pain."

In fact, Hyde is most animated when she's talking about this subject. Though she doesn't take stool samples from clients, she takes a detailed 80-question medical history relating to all aspects of health from her clients.

"Their symptoms show their gut bacteria is in a bad way because of high intakes of alcohol, which is like pouring weedkiller on intestinal flora, and regular antibiotics, which is like putting a nuclear bomb on it."

Then she puts them on her four-week gut makeover of seven cups of vegetables daily (two of them fruit), quality protein at each meal, no sugar, caffeine or alcohol; and, in the second half, "when their guts are ready for it", on probiotic foods such as kefir (fermented milk), roquefort cheese, miso soup and sauerkraut, before allowing them to slowly reintroduce "offending" foods - in small amounts.

Those who have been on Hyde's plan report weight loss of up to 6kg but what astounds Hyde are the additional benefits. "They sleep better and eczema, psoriasis or acne issues disappear." Her daughter, Hannah, had a chronic acne problem, which cleared up within three months. "They also report fewer pre-menstrual tension and menopausal symptoms, a reduction in bloat and fluid retention, more energy and a better mood. But that's not only shown in my clients, it plays out in the research, too - gut health is the key to overall health."

Healthy gut tips

Do

• Chew each bite 20 times.

• Eat lots of different varieties of vegetables to feed good bacteria.

• Eat probiotic foods such as sauerkraut, fermented cheese, miso soup and live yoghurt.

Don't

• Eat processed foods.

• Have too much sugar.

• Take antibiotics unless absolutely necessary.

The Gut Makeover by Jeannette Hyde (Quercus, RRP $34.99)