Weight loss diets – Are they good for the heart?

Obesity is an increasing health problem in Singapore. According to the National Health Survey, obesity rates increased from 6.9% in 2004 to 10.8% in 2010. Correspondingly, the diabetes rate has gone up from 8.2% in 2004 to 11.3% in 2010. Obesity is a well-known risk factor for cardiovascular disease and for the development of type 2 diabetes mellitus and the metabolic syndrome.

Therefore, there is an increasing interest in weight loss diets to combat obesity.

Most of these weight reducing diets reduce the caloric intake of food and encourage people to consume more plant-based food instead of animal-based food.

Currently, there is a greater interest in low carbohydrate diets to aid in the weight loss. The more popular approach for weight loss in the past was to cut the fat in the diet which makes logical sense if you want to lose fat.

Low carbohydrate versus Low fat diet

With the interest in a low carbohydrate diet sparked off by the Atkin’s diet, in the early 2000s, a number of randomised controlled trials which are the gold standard of research studies were carried out to compare if a low carbohydrate diet with high intake of fat and protein is able to reduced weight and other cardiac risk factors.

Two studies were published in the prestigious New England Journal of Medicine in 2003 to test the low carbohydrate, high protein/fat diet versus the low fat diet in obese individuals. Both studies showed that at 6 months, the patients on a low carbohydrate diet lost more weight than patients on a low fat diet, about 5-6 kilograms versus 2-3 kilograms. The low carbohydrate diet lowered the blood triglyceride levels (28% versus 1.4%) and raised the good cholesterol levels (18% versus 3.1%) more than the low fat diet. Both diets also helped to lower the diastolic blood pressure by about 6 mmHg and reduce the tendency to be diabetic by increasing the insulin sensitivity.

The reinforcement of the superiority of a low carbohydrate diet in weight lost came in 2007 when a study comparing the Atkin’s diet, Zone diet, Ornish diet and LEARN diet was published in another prestigious journal the Journal of the American Medical Association. In that study, the amount of weight loss from the low carbohydrate diet (Atkin’s) was much greater at 4.7 kilogram versus the rest at 2 kilograms over a one year period. Again, it was shown that the low carbohydrate diet raised the good cholesterol and lowered the triglyceride levels more than the other diets. The systolic blood pressure was lowered more by the low carbohydrate diet.

Long term effects of a low carbohydrate diet

The main problem in all the above studies is that the drop out rate for these diets was very high, mostly in the region of 20% to 40%, so long term adherence is a problem. It was also expected that with the reduction in the risk factors for heart disease such as cholesterol levels and blood pressure, there would be a corresponding long term benefit of this diet on the reduction of heart disease and mortality. However, there is a concern about the increase in fat and protein intake which may be bad for the heart.

Looking at the evidence available, the studies were all done in cohorts of people in various countries and the diet assignment was not randomised but observed and based on food questionnaires. A Japanese researcher performed an analysis of all the studies of the low carbohydrate diets and other diets found that there was an increase in all-cause mortality with the low carbohydrate diet over a follow-up of 10 years or more. In 2012, Lagiou published a study of a 15.7 year follow-up of the diets of 43,396 Swedes and found that a decrease of 920 grams of carbohydrate and a 5 gram increase in protein caused a 5% increase in risk for coronary heart disease. These data are surprising as one would expect that a low carbohydrate diet would lead to less not more heart disease or deaths from heart disease.

The answer may lie in a study by Dr Fung published in 2010 in the Annals of Internal Medicine. Dr Fung looked at two cohorts, the Nurses Health Study and the Health professionals follow-up Study involving more than 120,000 individuals who were followed up for more than 20 years. Dr Fung found that low carbohydrate diets using animal protein had a 31% increase in death, a 14% increase in death from heart disease in men and 32% increase in cancer deaths. However, with low carbohydrate diet with vegetable proteins, this association was not found and a protective effect of a 20% reduction in all cause death and 23% reduction of death from heart disease.

Best food choices in a low carbohydrate diet

This revelation then puts the focus sharply on the individual components of the diet.  The low carbohydrate diet has less than 30% of the energy coming from carbohydrates, the rest of the calories must come from an increase in fat and protein. The type and quality of the protein source is important as shown above. Red meats have been shown to increase risk of heart disease. In contrast, eating fish and poultry may be more beneficial as a protein source. We can also use plant protein as a source as well especially soy and soy products. The best evidence comes from a Japanese study published in Circulation in 2007. It involved 40, 462 Japanese and found that in women who took soy products more or equal to 5 times a week versus none to 2 times a week had a 36% lower risk of stroke and 45% lower risk of heart attacks and 69% lower risk of death from heart disease. Cutting down red meat or fatty meat consumption, but including more leafy vegetables (or non-starchy vegetables) will be able to give us a heart-healthier and fuller meal.

We can also encourage the intake of complex carbohydrates which are usually in the form of dietary fiber in fruits, vegetables, whole grains and legumes. The high dietary fiber intake was found to reduce diabetes risk. Greater whole grain intake (2.5 servings per day versus almost none) has been found in an analysis of 7 large cohort studies to lead to a 21% lower risk of heart disease events and a 17% lower risk of stroke.

Healthful versus Unhealthful plant-based diet

Plant-based diet is a board term as it includes all kinds of vegetable, fruit, and non-animal products. Without any further thought, most people would regard plant-based vegetarian diet as healthy although it may not always be the case.

A recent study published in the Journal of the American College of Cardiology 2017 reported highest adherence to healthful plant-based diet (which includes whole grains, fruit, vegetables, nuts, oils and tea) being associated with  a reduced risk of heart disease by 25%. Healthful plant-based diet is high in dietary fiber, antioxidants, unsaturated fat and micronutrient content and low in saturated fat, which will benefit those who require weight loss, better glycaemic control and insulin regulation, improved blood pressure and lipids profile, as well as good vascular health.

Conversely, highest adherence to an unhealthful plant-based diet, which includes intake of fruit juices, refined grains, potatoes and its products, sugar sweetened beverages, sweets and desserts, increased risk of heart disease by 32%.  Unhealthful plant-based diet was also associated with higher glycaemic load and index, excessive sugar intake, lower levels of dietary fiber, unsaturated fat, micronutrients and antioxidants, all of which can lead to higher risk of heart disease.

Although this study may not be able to rule out all other lifestyle and environmental factors which may contribute to the risk of heart disease, it adds to the current evidence that a healthy balanced diet with emphasis on higher healthy plant food intake can help with cardiovascular health.

What should we do then?

A low carbohydrate diet may be a good short term solution for weight reduction in obese individuals but it may not be very safe to maintain this diet for the long term. For the maintenance phase, it may be recommended to be on a Mediterranean diet as this diet has been proven to be effective in preventing heart disease. In a study published in the New England Journal of Medicine in 2013 involving 7447 high risk individuals over 4.8 years, the Mediterranean diet was associated with a 30% reduction in the risk of stroke, heart attack and death from heart disease compared to a control diet. The drop-out rate for a Mediterranean diet was low, less than 5% and was highly sustainable for the long term. It is hoped that with a proper diet choice along with emphasis on higher intake of plant-based food, we can then stem the epidemic of obesity that is engulfing Singapore and the world.

Dr Kenneth Ng, Consultant Cardiologist

Ms Lee Yee Hong, Senior Dietitian, Mount Elizabeth Novena Hospital


Low fat diet – A diet with reduced proportion of fat, which is usually less than 30% of total calories.

Low carbohydrate diet – The diet with lower carbohydrate, which is usually less than 30% of total calories or less than 130g carbohydrate/day.

Starchy vegetables – Vegetables with higher content of carbohydrate, it can be as high as 15g carbohydrate per serving. They are mostly the roots, bulbs or kernels of the plant, e.g.:  potatoes, sweet potatoes, corns, pumpkin, and so on.

Non-starchy vegetables – Vegetables with minimal starch content (lesser than 5g carbohydrate per 100g), usually comes with high fibre and low calorie. E.g.: cabbage, kale, lettuce, chye sim, broccoli, cauliflower and so on.

Wholegrains – Whole grains or wholegrain products must contain all the essential parts and naturally-occurring nutrients of the entire grain seed, which means that 100% of the original kernel, including all of the bran, germ, and endosperm must be present.

Mediterranean diet – Mediterranean diet encourages usage of olive oil as a healthier fat source to replace other saturated fat, high intake of fruit, vegetables including leafy green vegetables (or non-starchy vegetables), cereals, bread, nuts and pulses/legumes, low to moderate intakes of fish and other poultry, dairy products and red wine, and low intakes of red meat, eggs (0 to no more than 4 times/week) and sweets.

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