Interest in weight-loss diets as a way to combat obesity is growing.

And with obesity a growing health problem in Singapore, it would help to know if such diets can be used to combat this rising trend.

People who are obese are at a higher risk for cardiovascular disease, such as heart problems, as well as type 2 diabetes.

They are also more prone to the metabolic syndrome, which refers to conditions such as higher blood pressure or blood sugar, excess body fat around the waist and abnormal cholesterol levels.

In Singapore, obesity rates increased from 6.9 per cent in 2004 to 10.8 per cent in 2010. Correspondingly, the diabetes rate has gone up from 8.2 per cent in 2004 to 11.3 per cent in 2010.

LOW CARB OR LOW FAT?

Many studies have explored the dichotomy of a low-carbohydrate diet versus one that is low in fat.

In 2003, two studies published in the prestigious New England Journal Of Medicine found that obese patients on a low-carb diet lost more weight - about 5kg to 6kg - than those on a low-fat diet, who shed about 2kg to 3kg.

Those on a low-carb diet also saw a drop in their blood triglyceride and had elevated good cholesterol levels - more so than the group on a low-fat diet.

Both diets helped to lower the patients' diastolic blood pressure significantly and reduced their tendency to be diabetic.

Although the low-carb diet looks more promising, the drop-out rate was very high, which meant that long-term adherence is a problem.

There is also concern that the increased fat and protein intake may be bad for the heart.

More recently, a 2012 study by the University of Athens Medical School found that eating 920g less carbohydrate and 5g more protein per day may be bad for the heart.

The study, which tracked 43,496 Swedish patients for close to 16 years, found that those dietary changes led to a 5 per cent higher risk for coronary heart disease. The data was surprising as it was expected that a low-carb diet would reduce the likelihood of heart disease.

The answer may lie in a study by the Harvard School of Public Health, published in 2010 in the Annals Of Internal Medicine.

It involved the data of more than 120,000 people in the United States, who were followed up for more than 20 years. Its findings show that the type of protein in a low-carb diet makes a difference.

Animal protein refers to products such as meat and eggs, while vegetable protein can be found in soya beans and greens like broccoli. The group who mainly ate animal protein had an increased risk of chronic diseases and death. They were more likely to die from heart disease and cancer than those who mainly ate vegetable protein.

In fact, there was a protective effect for those who ate vegetable protein. They had a 20 per cent drop in deaths in general, including 23 per cent fewer deaths from heart disease.

WHAT SHOULD YOU EAT IN A LOW-CARB DIET?

This revelation puts the focus squarely on the individual components of the diet.

As the low-carb diet has less than 30 per cent of the energy from carbohydrates, the rest of the calories must come from fat and protein.

The type and quality of the protein source is important. Eating fish and poultry may be more beneficial as red meat - such as beef and pork - has been shown to increase the risk of heart disease.

Plant protein, particularly soy and soy products, can also be used.

A Japanese study published in the Circulation journal in 2007 found that women who took soy products at least five times a week had a 36 per cent lower risk of stroke, compared with women who ate soy-based foods at most twice a week. They also had a 45 per cent lower risk of heart attacks and a 69 per cent lower risk of dying from heart disease.

For a heart-healthier and fuller meal, cut down on red meat or fatty meat and eat more leafy vegetables.

NOT ALL PLANT-BASED DIETS ARE GOOD

A plant-based diet includes all kinds of vegetables, fruit, grains, nuts and seeds and processed products made from them, such as sugar, oil and bread. Most people would regard it as healthy although it may not always be the case.

A diet that features plenty of fruit juice, refined grains like white bread, potatoes and its products, sugar-sweetened beverages, sweets and desserts, can harm the heart.

In fact, a study published this year in the American College of Cardiology reported that people who regularly make such food choices had a 32 per cent higher risk of heart disease, although the diet is entirely plant-based.

This is because such unhealthful plant-based diets cause the person to consume higher amounts of sugar and less of beneficial nutrients, such as dietary fibre, unsaturated fat and antioxidants, that help to protect the heart.

In contrast, better choices in a plant-based diet will be whole grains, fruit, vegetables, nuts, oils and tea. The same study found that eating these items will cut one's risk of heart disease by up to 25 per cent.

LOW CARB IS FOR THE SHORT TERM

A low-carb diet may be a good short-term weight-loss solution for obese people, but it may not be very safe for them to maintain this diet in the long run.

To maintain their weight, they can consider going on a Mediterranean diet, which has been proven to be effective in preventing heart disease.

This type of diet encourages the use of olive oil in place of other saturated fat sources. It also features a high intake of fruit, leafy greens, cereals, bread, nuts, pulses or legumes.

Meanwhile, one should stick to a low to moderate intake of fish and other poultry, dairy products and red wine, and eat minimal amounts of red meat, eggs and sweets. Doing so has been shown to lower the risk of stroke, heart attack and death from heart disease by up to 30 per cent, compared with a control diet.

These findings, which involved studying about 7,500 people at high risk of cardiovascular disease for about five years, were published in the New England Journal Of Medicine in 2013.

Another good thing about the Mediterranean diet is that the drop-out rate was low - less than 5 per cent in the study. This indicates that it can be sustained for the long term.

Hopefully, a proper choice of diet, along with a higher intake of plant-based food, can help us stem the epidemic of obesity that is engulfing Singapore and the world.

•Dr Kenneth Ng is a consultant cardiologist at Novena Heart Centre. He wrote this column together with Ms Lee Yee Hong, a senior dietitian at Mount Elizabeth Novena Hospital.