She says ‘no, thank you’ to chocolate, nuts, oats and avocado because of genetic disorder

SINGAPORE - Not eating oats, nuts, avocado or things cooked in olive oil may sound like a dream diet to some meat lovers, but this is the special diet that 23-year-old Tiew Hiew Tung has to stick to – for life.

She also cannot eat chocolate as freely as others.

The special diet was prescribed to Ms Tiew to prevent her from having serious health issues.

As she has sitosterolemia,

a rare genetic disorder,

her body is unable to remove plant sterols, which are natural compounds in plants structurally similar to cholesterol.

Instead, her body absorbs large amounts of the sterols, causing a build-up of fatty deposits, similar to patients with familial hypercholesterolemia (FH).

Patients with sitosterolemia may have symptoms like those of patients with FH, including fatty lumps under the skin or on their tendons, as well as early atherosclerosis – or hardening and narrowing of the arteries – which can lead to heart attacks or strokes even in children.

Ms Tiew, who has just completed her studies in biological sciences at Nanyang Technological University, was initially treated as a patient with FH from around 2010.

She started taking medication and more plant-based food to manage her blood cholesterol levels.

However, as her blood test results did not show much improvement, she went for genetic testing a few years ago, which confirmed that she had sitosterolemia rather than FH, and that her diet should be the direct opposite – avoiding plant-based food instead of consuming more of it.

“Based on the new diet, I cannot eat foods like nuts, avocado and seeds, which is fine with me as I do not like these anyway. The most difficult thing to adjust to is cutting down on chocolate, as I like chocolate, and it is quite hard to avoid it as there are hot cocoa, chocolate milk and plenty of desserts with chocolate,” said Ms Tiew.

Based on a Japanese study published in the Journal of Atherosclerosis and Thrombosis in April 2021, patients with sitosterolemia should avoid foods rich in plant sterols, such as corn oil, sesame seeds and oil, peanuts, soya beans, margarine, avocado, chocolate and shellfish.

They should also avoid cholesterol-rich foods, including animal liver and eggs.

Ms Tiew’s elder sister, now aged 25, was the first in the family to be diagnosed with the rare condition around 2010, due to fatty lumps on her skin, which turned out to be lipids after a biopsy.

Ms Tiew was subsequently diagnosed, followed by her younger brother, now aged 19.

She had suffered symptoms, like fatty lumps on her elbow, that were similar to symptoms of patients with FH, but there was great improvement after she commenced treatment for sitosterolemia.

As all three siblings have the same condition, and genetic testing confirmed they inherited genes with mutations from both parents, the whole family is now on a healthier diet regime – cooking more healthily at home with less oil and more steamed food, and minimising eating out.

On occasions when she eats out, Ms Tiew asks for less oil to be used in cooking, as most cooking oils are plant-based.

She is currently still receiving care at KK Women’s and Children’s Hospital (KKH) Children’s Lipid Centre, with follow-up consultations every six months and a cardiology test each year.

Professor Fabian Yap, KKH’s head and senior consultant of endocrinology service, said that while the

majority of patients at the centre have FH

, Ms Tiew’s case showed the importance of conducting genetic tests “so that we can diagnose it correctly, and offer the right advice in managing the condition”.