Mrs Sacha Baron Cohen, Isla Fisher on family life and her role in 2013’s most hotly anticipated film, The Great Gatsby

It’s nutritious and doesn’t cost a penny, yet breast-feeding is in decline in many parts of the world. Elaine Lipworth joined actress and mother Isla Fisher on a trip to Brazil to find out how a milk-donation scheme is bucking the trend – and slashing infant mortality rates.

In the maternity wing of a state-run São Paulo hospital, Isla Fisher is sitting on a narrow bed beside student Bianca Novais who is breast-feeding infant son Gustavo. ‘Ah, he’s so cute,’ says Isla. Contented, the baby closes his eyes. Bianca, a pretty young single mother, smiles and hands her son over to the actress. Isla looks tenderly at the baby, dressed in a green romper suit, rocks him gently and says, ‘Oh, I want another baby now.’

Isla is completely at ease with Gustavo, having two daughters herself – Olive, five, and two-year-old Elula – with Borat-star husband Sacha Baron Cohen. In broken English, 20-year-old Bianca tells Isla that she is still at high school, hopes to become a vet and is here donating milk ‘to help babies become healthy when their mothers can’t feed them’.

‘You are an angel,’ says Isla, handing Gustavo back to his mother. ‘She had a complicated labour,’ Isla tells me. ‘She’s breast-feeding and pumping manually – I used a machine – then sterilising containers and storing her breast milk, and she’s still at school. She’s amazing.’

Isla, 37, who grew up in Perth, Western Australia, and now lives in London, is here in her new role as ambassador for the UK-based global charity Save the Children. Accompanied by her brother Eddie, 35, an artist, it’s her first time in Brazil. I’ve joined the star of Wedding Crashers, Confessions of a Shopaholic, Definitely Maybe and the upcoming remake of The Great Gatsby (Isla plays Myrtle opposite Leonardo DiCaprio, Carey Mulligan and Tobey Maguire) to meet families who are taking part in a pioneering, long-term breast-feeding and milk-donation programme. Run by the Brazilian government, it has had a huge impact on infant mortality, helping to slash death rates of children under five by 50 per cent.

Isla breast-fed both her daughters for two years. ‘Having my child on my chest was one of the most wonderful experiences of my life. My mother breast-fed me and I’ve always been that annoying person rattling off stats about the health benefits,’ she says. She is indeed impressively knowledgeable on the subject, from the nutritional significance of ‘the mother’s first milk, colostrum, essential for boosting a baby’s immune system’, to the pluses for mothers, ‘such as helping to prevent breast cancer’.

We are in the sprawling city of São Paulo, South America’s biggest metropolis – population 11 million – to highlight a major new Save the Children report, Superfood for Babies, which draws attention to the hugely successful Brazilian programme and, at the other end of the spectrum, the disturbing statistics in the developing world. In countries such as Liberia and Sierra Leone, one child in six dies before their sixth birthday.

Mothers often feed their children formula mixed with dirty water. Breast-feeding can make the difference between life and death, yet the practice is declining across many parts of Africa and Asia, partly due to the influence of witch doctors, but also because of aggressive marketing from pharmaceutical companies promoting formula.

Hospital Regional Sul is in one of the poorest parts of São Paulo. The country that is hosting the 2014 World Cup and the 2016 Olympics has a booming economy, but the gap between rich and poor is staggering. We travel in a bulletproof car with Herbert our bodyguard (the city is notorious for its street crime) through the concrete business district dominated by Manhattan-style skyscrapers, before crossing into the impoverished South District. The hospital is a stone’s throw from the city’s drug- and crime-infested favelas (slums), where families live cheek by jowl in shacks constructed from bare brick with corrugated iron roofs.

It is hot and muggy – the height of Brazil’s summer – and outside the run-down hospital, pregnant women in sundresses clutch children, many barefoot. Inside, the atmosphere is welcoming, but it’s clear from the shabby furniture and chipped mosaic flooring that resources are in short supply. In Brazil – as in the US – the well-off can afford health insurance for private care, while the uninsured rely on medicine provided by the state.

But there is a great pride among staff here. We’re treated to snacks served in Isla’s honour; the actress helps herself to coffee and biscuits, then listens intently as paediatrician Dr Rosangela Gomes shows us around the Banco De Leite Humano (human milk bank). A huge fridge is filled with milk collected from volunteer mothers such as Bianca, sterilised, pasteurised and stored in recycled coffee and jam jars donated by the local community. ‘The fact that Brazil has 210 milk banks, one in every hospital, is amazing,’ says Isla.

Vivacious, with a sunny personality, the beautiful redhead, dressed in bright green cropped jeans and a white T-shirt, breezes around the wards. She chats to 18-year-old single mum Jucicleide Jesus de Lacerda and her newborn baby, and poses for pictures.

Visibly affected by the entire experience, Isla admits she is missing her own children. ‘They are fine, they’re with their dad,’ she says, fighting back tears as we chat over cappuccinos later that evening [the family is currently staying at their Los Angeles home]. ‘It’s the first time I’ve left them – they travel everywhere with me. I’m OK, but it’ll be hard tonight.’ She’s made an exception because she’s passionate about the cause and has a personal connection to the charity. Her Scottish father Brian was a senior executive for Save the Children in the 1980s. ‘It was when Save the Children was involved in the clearance of land mines in Cambodia,’ says Isla, ‘so when I got the email and saw the logo I felt very sentimental.’

Isla has fond memories of a visit to Western Australia by the charity’s president Princess Anne, organised by her father. ‘That was a big deal. Dad still has a photo of himself with her at the Save the Children ball. He loves Princess Anne and I was a huge Diana fan. I drew pictures of her with the Queen and sent them to her when I was six. She actually wrote back thanking me for “my wonderful drawings”. My friend Naomi [Watts] is playing her in a movie, which I can’t wait to see.’

Isla won’t discuss her own family in any detail (‘My kids didn’t choose to be famous’), but she talks about her own upbringing in Perth with her mother, writer Elspeth Reid, her father, who worked for the UN before Save the Children, and her two brothers. ‘We travelled a lot and I went to a different primary school every year. I actually think people find me funny because I needed to make friends quickly as a child and tapping into my inner idiot is a great way of connecting to strangers.

‘I wasn’t raised with any discipline at all [her parents divorced when Isla was nine, and she has two stepbrothers]. Mum let us throw massive parties in the house when we were teenagers. Her argument was, “If you’re going to get up to mischief, it’s far better to be doing it under my roof.” She would lock herself away so that she didn’t have to listen to us while we drank Victoria Bitter!

‘Maybe that’s why we all ended up doing creative things,’ says Isla. ‘I do think that children learn by watching their parents, rather than just doing what they’re told. I learned from Mum to be analytical, open-minded, gregarious and very optimistic.’

She was also fiercely independent. ‘I didn’t finish high school and left home at 16. I spent my life on TV and movie sets and in theatres,’ she says. She moved to Paris in 1997, aged 21, and studied at the late mime artist Jacques Lecoq’s school, before her film career took off. ‘I’ve had a nomadic lifestyle, but I’ve always been close to Mum. We’ve just written a screenplay together – it’s a thriller.’

She grins. ‘I highly recommend writing with a family member. It’s a scream – a couple of gin and tonics and a lot of giggles.’ The following morning, Isla is in good spirits, though she woke in the early hours, jet lagged, waking Eddie to keep her company. ‘We watched an episode of Homeland, ordered room service and mucked about.’

They obviously get on well. ‘We do now, but when we were younger, he and my other brother used to tease me and do horrible things – a lot of “dead legs” and wrestling moves were tried out on me. But it all helped me to grow up to be the strong lady I like to think I am now.’

Isla and I are driven into another poor neighbourhood north of the city, along streets lined with grey, dilapidated buildings covered in angry graffiti. There’s an enthusiastic welcome from staff at the Leonor Mendes De Barros Maternity Hospital. Isla has a word with mothers and nurses in the natural-birth room. We find out that 92 per cent of women have caesareans in Brazil’s private sector. (‘We’re all familiar with the too-posh-to-push syndrome,’ says Isla with a wry smile.) That figure drops to 34 per cent in state hospitals.

‘I was lucky that I had natural births. I fed on demand, and when I shot Confessions of a Shopaholic [2009] after the birth of my first baby, I had it in my contract that I would breast-feed every three hours for 20 minutes. But some mums can’t do it – perhaps they’re suffering from postnatal depression or they had difficult labours.’

We visit the hospital’s milk bank, then put on scrubs and tiptoe into the hushed intensive care unit, where the walls are painted with bright murals. Isla hovers over an incubator, peering through the glass at Kimberly, a premature baby girl who is receiving donated breast milk. Her mother had a difficult delivery, is suffering from hypertension and can’t breast-feed the infant herself. ‘Kimberly’s going to make it, isn’t she?’ asks Isla anxiously. She’s assured that the baby is on the road to recovery.

Milk is collected not only in the hospital but from volunteer mums in the area, too. Ambulances, fire crews and local women act as ‘milk men’, collecting supplies. Today, an ambulance whisks us along with a nurse to a nearby block of flats. Carolina Alfonso Pinto, a 36-year-old engineer, and her PE-teacher husband Fabio live on the 21st floor with their six-month-old son Rafael. They are thrilled to meet Isla – they loved her in Confessions of a Shopaholic.

Carolina fetches a large bottle of frozen breast milk from the freezer and hands it to the nurse. Isla sits on the sofa cuddling Rafael. ‘He is so handsome, I could eat him up… I feel like I’m ovulating just being here,’ she jokes. It’s hard to drag her away.

‘It really puts you in touch with your own humanity,’ comments Isla, ‘because everything comes down to what’s essential for a newborn baby – breast milk. Women like Carolina don’t want a pat on the back, they’re just doing it for other mothers.’

Isla knows she is lucky that she can take her children to work. ‘The upside of acting is that they give you a space on set where your children can be with you. I feel guilty even saying that because that’s not possible for a lot of working women. If I had to go to an office from nine to five it would be different.’

Family life means that Isla is more discriminating about the work she takes on. Playing Myrtle in the F Scott Fitzgerald classic was ideal: a challenging supporting role, shot in Australia. It was also ‘a dream’ to work with a fellow Australian in director Baz Luhrmann. ‘I loved Myrtle because she was one of the few representations of the lower class in the movie,’ says Isla. ‘My character gets to escape from her class and have this wonderful affair with Tom Buchanan [played by fellow Aussie Joel Edgerton].’

Later this year she will take on her first action role, as an escapologist in Now You See Me. ‘My first instinct was to decline the role when I heard I’d be chained underwater in a tank, because I’m a scaredy cat, but I thought it would be good for me.

I got to do stunts – I really understand the lure of action now.’ There are no specific career goals. ‘I think life is an open book, and I just turn the page. I have only been ambitious sporadically and without much strength,’ she says. ‘You know, I was on Home and Away when I was younger and I did repertory theatre for no money, where you actually pay to do it. So the fact that I’ve worked with amazing directors like Baz still feels surreal. I don’t understand how it happened, but I hope no one finds out and stops it.’

There are no plans to stay at home full time, but ‘being a mummy takes precedence. I do feel incredibly blessed. When I was young, all I wanted to do was to get married and have kids. I know that sounds like a cliché but it’s true.’ And with that she heads off to the airport for a midnight flight that will land her in LA just in time for lunch with the family.

To support Save the Children go to savethechildren.org.uk; The Great Gatsby will be in cinemas on 17 May