"Once you've achieved the first 30 days, there will be no turning back," she promises, "you will make definite lifestyle changes for the better as you'll feel so energised and full of life."
Natasha, who is engaged to Simon Bateman, 36, a fitness expert, comes from a family who know about food. Her mother, the interior designer Kelly Hoppen (Sienna Miller is her stepsister) was always a "health freak", she says, and the fridge at home was full of "dairy-free milk and similar products".
From her father Gerald Corrett, a restaurateur, owner of fashionable Le Boudin Blanc in Mayfair, Natasha developed a fondness for good food, learning to cook at his restaurant during her school summer holidays. Like many of us, she admits she has always been torn between knowing what is "good for you" and not wanting to deny herself a dish she enjoyed.
So what led to her passion for "the alkaline way"?
"Five years ago," she explains, "I was always on the go, making and delivering fresh food for my company Fridge Fill, working hard but not making a living, and feeling tired all the time." In addition, Natasha admits that being dissatisfied with her weight and years of yo-yo dieting meant she was on the verge of an eating disorder.
"When I was at boarding school, it was fashionable to be really skinny and my weight fluctuated massively as I tried to fit in."
It was her mother who recommended a therapist specialising in Ayurvedic medicine as well as acupuncture. When he pointed out that Natasha's whole system was out of balance, she was more than ready to listen. "The therapist told me my body had become incredibly acidic from years and years of yo-yo dieting, even though I thought I was super-healthy, being vegetarian and knocking back a green smoothie with spirulina every morning," she says.
"He suggested my body was in such a toxic state from stress and overwork that there was no way it could absorb the nutrients I was consuming. He said I needed to do an alkaline cleanse."
Claims as to the benefits of an alkaline diet are not new. Pioneered by Dr Robert Young, an American biologist, the theory is that the digestive process causes foods to become either alkaline or acidic, as measured by their pH levels. The results are sometimes counter-intuitive: dairy, for example, becomes highly acidic when digested, while lemons become alkaline.
Fans of alkaline eating maintain that while alkaline-forming foods help the body maintain healthy pH levels, too much acidity does the opposite; and that sticking to an alkaline diet can help with weight loss and bloating as well as improving digestion, skin tone and mood. An acid-based diet is blamed for diseases such as osteoporosis, heart problems, back pain and kidney stones.
"At first, I wasn't sure I wanted to try this way of eating," says Natasha. "I had promised myself I would never do another detox or diet, as I had become so obsessed with food and felt so unhappy. I had sworn never to put myself through that misery again. But I was persuaded to try an alkaline cleanse for 21 days, and in the end, I just didn't stop. I felt so well."
Gradually, the weight came off, while her symptoms of PCOS - acne, mood swings and bloating - disappeared as her hormones became more balanced.
Whether or not the theory holds up, much of the advice on alkaline eating chimes with official guidance on a healthy diet. Natasha advocates replacing acid-forming foods with alkaline foods - fruit, vegetables, pulses and wholegrains. Wheat is also considered acid-forming, while almonds, garlic, olive oil and herbal teas are highly recommended.
As Natasha points out, following this way of eating is mostly common sense and her delicious recipes prove it need not be painful. "Think about eating as Mother Nature intended," she advises. "Make your diet plant-based, with lots of pulses and grains, although don't eat too much fruit - certainly not on an empty stomach, as that is very acid."
She recommends following the alkaline pattern of eating 70 per cent of the week and then relaxing about the other 30 per cent. "And if you can't resist meat on a 30 per cent day," she says, "just be sure that all the meat you buy is organically and sustainably reared."
Exercise plays a large part in Natasha's life and complements her system. "When I'm feeling low or tired, a burst of activity just gets the 'happy hormones' [endorphins] pumping around my body, and in that state I find that I naturally reach for healthier foods. What's more, research has shown that just eating healthy food can boost endorphins in the brain - so combine that with exercise and you'll double the hit."
She blogs enthusiastically about the alkaline lifestyle at honestlyheathyfood.com, and runs occasional cookery classes, too. There's also a recipe app, and Londoners can join the Honestly Healthy supper club. Naturally, both mother (for health) and father (for taste) approve of her venture. Best of all was a surprise endorsement from one of the UK's leading chefs, Marcus Wareing, who, Natasha was thrilled to learn, cooks from her books at home.
"Natasha has a really creative, inventive and forward-thinking attitude to food and cooking," he says on the book's cover. "That was my Michelin star," she says proudly.
"What's important to me is how can we get to optimum health," she adds. "It's what is going on inside that matters, not about how you look. And if you follow a healthy diet, your skin will glow and the weight will drop off. But the food has to taste good, too."
Which cleanse is right for you?
Each of the four cleanses in Honestly Healthy Cleanse is designed to fit in with your lifestyle, depending on whether you want a weekend cleanse, a pre-event slim down or a cleanse for heavy exercise.
1. Feelgood
A two- or three-day liquid cleanse, comprising smoothies, juices, teas and soups - all designed to give your body a rest from digesting and to help draw out the toxins naturally.
2. Slim down
This six-day cleanse will give you a gentle kick-start to shift any extra pounds before a party, holiday or special event. You'll be eating raw salads with soups and smoothies, which will boost your immune system.
3. High-energy
This six-day cleanse is designed for people who are exercising a lot, who want to find out how to get more vegetarian protein into their daily diet and cleanse their body at the same time.
4. Life-changing
This 30-day cleanse is a stepping stone
to a new, healthier you. Once you've achieved the first 30 days, there will be no turning back - you will make definite lifestyle changes for the better as you'll feel so energised.
