Understanding Obesity

What is Obesity?

Obesity affects not only our physical appearance but also our health. The normal ranges of body fat percentage are 12% - 19% in men and 25% - 32% in women. Obesity results from abnormal or excessive body fat accumulation. Obesity is recognised as a disease by the World Health Organization (WHO) and may be accompanied by a wide range of chronic diseases.

Am I obese?

To diagnose obesity, we have to determine the amount of fat in our body. Body fat can be measured by hydrostatic weighing, skinfold test and magnetic resonance imaging. However, these methods are complicated and are not routinely used in clinical settings.

1. Body Fat Percentage

Overweight and obesity are defined as abnormal or excessive body fat accumulation. Our body fat storage depends on our gender and age:

*Percentage of body fat cutoffs by sex, age, and race-ethnicity in the US adult population from NHANES 1999-2004. Heo M1, Faith MS, Pietrobelli A. Heymsfield SB. AM J Clin Nutr. 2012 Mar;95(3):594-602. doi: 10.3945/ajcn.111.025171.Epub 2012 Feb 1.

2. Body mass index

Body mass index (BMI) is most commonly used to assess body fat mass. Clinical research showed a strong correlation between BMI and body fat mass as measured by magnetic resonance imaging.

Body mass index is calculated using the following formula:

Body mass index (BMI) = Body weight (kg) ÷ Body height (m) ÷ Body height (m)

According to the WHO Asia-Pacific guideline in 2000, adult BMI can be categorised as follow:

Body Mass Index Underweight Normal Overweight Obese I Obese II
BMI (kg/m2) <18.5 18.5-22.9 23-24.9 25-29.9 ≥30.0

3. Waist circumference

Recent studies have indicated that in addition to total body fat mass, body fat distribution also affects our health. Abdominal fat accumulation, also termed “central obesity”, is particularly harmful. Waist circumference is a good marker for central obesity. According to the WHO Asia-Pacific guideline in 2000, central obesity is defined as:

Ideal waist circumference Male Female
Less than 90cm
(35.5 inches)
Less than 80cm
(31.5 inches)

Prevalence of obesity in Hong Kong

Based on the Population Health Survey (PHS) 2014/15 conducted by the Hong Kong Department of Health, 29.9% (24.4% of females and 36.0% of males) of people were obese. This figure is significantly greater than in 2003/04 during which 21.1% (20% of females and 22.3% of males) of people were obese. Furthermore, in 2014/15, 5.3% of people were classified as Class II obesity (BMI ≥ 30.0 kg/m2).

Even though obesity is common, Hongkongers are not familiar with health facts related to obesity. Based on a survey conducted by the Hong Kong Association for the Study of Obesity in 2018:
  • 44.2% of interviewees did not regard obesity as a disease.
  • 70.9% of interviewees were not aware that the WHO has defined obesity as a disease.
  • 72.5% of interviewees did not know the BMI cut-off for overweight and obesity.
  • Interviewees who underestimated their body weight tend to have more obesity-related diseases including type 2 diabetes, high blood pressure, high blood lipids and fatty liver disease.

Health consequences of obesity

Obesity is a risk factor for many chronic diseases and is linked to premature death.

How to tackle obesity?

Obesity is a multifactorial disease caused by intake of energy-dense diet, lack of physical exercise, genetic factors, side effects of drugs and certain diseases. Out of these risk factors, unhealthy lifestyle contributes the most to the high prevalence of obesity in our society. The fundamental principle for weight reduction is to create a negative energy balance: a reduction in energy intake and an increase in energy expenditure. Diet and exercise therefore remain the cornerstone for successful weight control.

Causes of obesity

  1. Excessive energy (calories) intake
  2. Lack of physical exercise
  3. Other factors such as genes, side-effects of drugs and certain diseases
To lose weight, it is suggested that a deficit of 3500-7000 calories per week, or 500-1000 calories per day, be maintained through reducing energy intake and/or increasing physical activity. Sustained adherence to these recommendations can result in weight loss of 0.5-1kg (1-2 pounds) of body weight (fat) per week in most people.

Weight management concept

Maintain body weight: energy intake = energy expenditure
Weight loss: energy intake < energy expenditure
Weight gain: energy intake > energy expenditure

Managing obesity in daily life

10 dietary advices for weight loss

  1. Reduce energy intake and increase physical activity in order to create a negative energy balance.
  2. Choose healthier cooking methods such as steaming, baking, stewing, boiling and roasting. Avoid deep-frying and heavy sauce such as white sauce, Portuguese sauce and curry.
  3. Choose lean meat and its substitute, consume 3 taels (3 pieces of Mah Jong size or 1 palm size) of lean meat per meal at most, such as lean pork, tofu, egg and fish.
  4. Increase dietary fibre intake by selecting dishes with vegetables. Consume at least half a bowl of cooked vegetable per meal.
  5. Avoid excessive intake of alcohol and energy-dense drink.
  6. Eat until 80% full, avoid overeating.
  7. Avoid excessive hunger before mealtime.
  8. Chew thoroughly and avoid eating too quickly.
  9. Quality over quantity, avoid ordering too many dishes in a meal.
  10. When eating out, choose EatSmart restaurant and select “More Fruit and Vegetables” dishes and “3 Less” dishes (less fat or oil, salt and sugar).
Appropriate energy intake is the key to weight loss. All the foods can be divided into 3 categories:

Category Example
First category
Low in calories, eat freely
  • Green leafy vegetable and gourd: choi sum, spinach, broccoli, winter melon, hairy gourd, bell pepper
  • Mushroom and fungus: snow fungus, black fungus, straw mushroom, Lily bud
  • Seasoning: vinegar, pepper powder, ginger, spring onion, garlic, chili, Sichuan peppercorn, anise star, and other herbs (can add a little salt, soy sauce and sugar)
  • Plain Oolong tea, brown rice tea, green tea, red tea, chrysanthemum tea
  • Water, black coffee, lemon tea without sugar, lemonade without sugar, plain soup
Second category
Contain essential nutrients, eat adequately
  • Grains: rice, congee, noodles, bread, bun, biscuits
  • Starchy vegetable: potato, taro, sweet potato, carrot, pumpkin, corn
  • Beans: red beans, green beans, soybeans, chestnut, tofu, soy milk
  • Fruit and fresh juice
  • Dairy products: skim milk, low fat milk, low fat yogurt, low fat cheese
  • Meat: lean pork, lean beef, fish, seafood, poultry, egg
Third category
High in calories, sugar and fat, eat less
  • Added sugar: white sugar, brown sugar, rock sugar, fructose, honey
  • candy
  • Sugary drink: soft drinks, tetra packed juice, 3-in-1 drink, condensed milk
  • Sweet biscuit, sweet bun and cake: cream biscuit, cookies, pineapple bun, egg tart
  • Canned food: luncheon meat, sausage, cream soup
  • Fatty meat, chicken skin, pork knuckle, offal

Advice on exercise

  • Physical exercise should involve a combination of main muscle movement and an increase in heart rate.
  • Adjust your mind-set. Realise that exercise can help to reduce body fat, even though the body weight does not drop significantly.
  • Make exercise a habit and exercise regularly.
  • Increase the intensity and frequency of exercise gradually over time.
  • Adults should have muscle-strengthening exercise at least 2 times per week and moderate-intensity aerobic exercise (for example, brisk walking, running, swimming and cycling) at least 150 minutes per week.
  • Be physically active in daily life, for instance, taking the stairs instead of elevator and getting off a stop earlier so as to walk further.

Exercise and weight loss Q & A

Exercise helps to burn excessive energy and maintain our body shape. It can also improve heart and lung function, muscle mass and bone density. What do you need to know if you want to lose weight through exercise?

Q:Which types of exercise should I do?
A:According to the WHO1, adults should have muscle-strengthening exercise at least 2 times per week and have moderate-intensity aerobic exercise at least 150 minutes per week.

Q:I have knee pain. Which types of exercise are suitable for me?
A:Some people who are overweight or obese experience knee pain, muscle pain or skeletal problems. They should choose exercise according to their fitness and ability. For example, they can choose non-weight-bearing exercises such as cycling, swimming and exercise in water.

Q:Am I suitable for high-intensity exercise?
A:Some people who are overweight or obese may have heart disease. It is therefore important to consult your doctor before starting any exercise plan. In addition, you should pay attention to bodily symptoms including palpitation, chest tightness, chest discomfort and excessive shortness of breath during exercise. If you experience these symptoms, you need to stop the exercise and consult your doctor.

1 World Health Organization. Global recommendations on physical activity for health.

Drug therapy

Registered drugs for the treatment of obesity in Hong Kong:

Drug Function Target Side-effects Usage
Phentermine Inhibit appetite For people whose BMI is over 30.0 kg/m2, or BMI over 27.0 kg/m2 and have comorbidities, this drug can be used together with diet control and exercise to control body weight. Long-term usage can lead to serious side-effects, such as severe pulmonary vascular disease and heart problems. Approved for short-term use only (3 months or below)
Orlistat Prevent digestion and absorption of fat in our body For people whose BMI is over 30.0 kg/m2, or BMI over 27.0 kg/m2 and have comorbidities, this drug can be used together with diet control and exercise to control body weight. Steatorrhea (fat in stools), incontinence Approved for use to treat obesity
Liraglutide Increase our sense of fullness, reduce hunger sign For people whose BMI is over 30.0 kg/m2, or BMI over 27.0 kg/m2 and have comorbidities, this drug can be used together with diet control and exercise to control body weight. Mild side-effects such as nausea, diarrhoea, constipation. Approved for use to treat obesity


DO NOT buy slimming products from the market.

There are many slimming products in the market. Some of these products are not registered as western drugs and have not been properly researched on their safety, efficacy and quality. People who want to take medications to treat obesity should consult medical professionals and should not use any unevaluated product from the market.

Drug treatment is only effective when used in conjunction with lifestyle modification

Current research on drug treatment for obesity has shown that drug treatment together with lifestyle modification have a better outcome in weight reduction. Drug treatment is not a substitute for lifestyle modification and it is strongly recommended that people initiating drug treatment be fully adherent to a healthy lifestyle in order to maximise their chance of successful weight reduction.

Drugs for weight reduction Q & A

According to a survey conducted by the Hong Kong Association for the Study of Obesity in 2018, 67.3% interviewees worried about the side-effects of drugs for treating obesity. Many people have the same question, are those drugs safe?

Q:Are those drugs safe?
A:In clinical evaluation of drugs for the treatment of obesity, drugs that had severe side-effects were prohibited for further development and distribution. All the currently approved medications have been fully evaluated in clinical trials to demonstrate effectiveness and an acceptable safety profile. Furthermore, these drugs are prescribed by a doctor and are deemed safe to use after a medical assessment. Recently, a new class of drug – glucagon-like peptide 1 receptor agonists (GLP-1 RA) (Liraglutide) – has been approved for use in the treatment of obesity. This drug helps manage our body weight while having minimal side-effects. By altering the hormonal system, it increases the body’s sense of fullness, reduces the sign of hunger, and helps control our food intake in long-term. If the individual also exercises regularly, the weight loss effect would be more substantial.

Q:Can we use those drugs for the long term?
A:Not all the approved drugs can be used long-term. Long-term usage of phentermine may have adverse effects on the heart and lungs and is not recommended for long-term weight management.

Q:Are all GLP-1 RA suitable for weight reduction?
A:To date, only one type of GLP-1 RA (liraglude) is approved by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the treatment of obesity. If you have any inquiries, please consult your doctor.

Bariatric surgery

For morbidly obese individuals, an effective weight reduction therapy is not for cosmetic reason but for treating a serious health problem. To date, evidence has shown that bariatric surgeries are safe and effective methods for weight management for morbid obesity.

  • In 1991, National Institutes of Health in the US recognised that bariatric surgery is the only long-lasting and effective way to lose weight. They recommended morbidly obese people to receive bariatric surgery for weight reduction with the aim to lower the risk of premature death. In 2015, the 2nd Diabetes Surgery Summit provided a consensus that bariatric surgery is a potentially cost-effective treatment option for obese people with type 2 diabetes. Currently, there are several types of bariatric surgery. Although the surgery has risks and side-effects, the amount of weight loss is often pronounced and sustained. After successfully losing weight via bariatric surgery, many metabolic diseases and symptoms can resolve or be improved, especially in those with type 2 diabetes. The surgery helps control our calories intake, reduce absorption rate, and improve insulin sensitivity. Food can enter the terminal part of intestine quicker so that incretin (a special gut hormone) can be released quicker to stimulate insulin production and lower blood sugar.
  • In Asia-pacific area, according to the consensus of International Federation for the Surgery of Obesity and Metabolic Disorders Asia Pacific Chapter in 2011, bariatric surgery can be considered for the treatment of obesity for acceptable Asian candidates with
    1. BMI ≥ 35.0 kg/m2 with or without comorbidities
    2. with BMI ≥ 30.0 kg/m2 with severe obesity-related diseases
  • In 2015, the 2nd Diabetes Surgery Summit provided a consensus and suggested that poor diabetic control obese I (BMI 27.5-32.5kg/m2) type 2 diabetes Asian patient can consider metabolic surgery.
Standard metabolic surgical procedures

1. Laparoscopic Adjustable Gastric Banding

The adjustable gastric band is made of soft silicone. It is adjusted by injecting saline into the port. The size of the band depends on the weight management plan and is tailor-made for patients. The band is positioned around the upper part of the stomach, forming a small pouch. It can help reduce the amount of food that a person wants to eat by inducing a sense of fullness after eating only a small amount of food. Although the weight reduction effect is less than that of gastric bypass or gastrectomy, it is relatively safe compared with other bariatric procedures. One of the drawbacks of this type of surgery is that the band will stay inside the body of the person permanently. Although this surgery helps reduce food intake, if the person continuous to consume energy-dense foods such as sugary drinks, ice cream, chocolate, etc., the expected amount of weight loss cannot be achieved.

2. Laparoscopic Sleeve Gastrectomy

"Sleeve gastrectomy" or "vertical gastrectomy" is a new form of bariatric procedure in weight management. It involves the removal of part of the stomach and leaving a small gastric tube. This leads to a decrease in the stomach size, an increase in the patient’s sensation of fullness, and eventually causing a decrease in appetite. Furthermore, the surgery removes the secretion site of appetite-stimulating hormones and therefore increases satiety. However, since the surgery involves removal of part of the stomach, there is a potential risk of leakage and bleeding. Gastric-reflux may occur after this surgery and long-term medications may be needed. Before deciding to receive this irreversible surgery, patients should have a thorough understanding of the procedures and potential risks.

3. Laparoscopic Gastric Bypass

In the gastric bypass surgery, the stomach is divided into a small upper pouch and a much larger, lower "remnant" pouch. The volume of small pouch is only 20-50ml. The small intestine is re-arranged to allow food to enter distal small bowel without passage of the remnant stomach, duodenum and proximal jejunum (150-200cm of small intestine in total). Since the size of the stomach is reduced, the eating portion becomes smaller and the absorption area in the small intestine is shortened; thus, rapid weight loss is expected. This is a complicated surgery which requires a long operation time, so there is a risk of leakage and bleeding. After the surgery, absorption of many essential nutrients and vitamins become limited and many people will require nutritional supplements on a daily basis. Iron supplementation can prevent iron-deficiency anaemia. Calcium supplementation can prevent osteoporosis. The advantages of this surgery include provision of a faster weight loss and a lower chance of weight regain. This surgery also effectively treats type 2 diabetes. Most of the people with diabetes have significant improvement after surgery, and some of them may be able to wean off their diabetes medication altogether.

4. Laparoscopic sleeve gastrectomy with duodenojejunal bypass

This surgery includes sleeve gastrectomy and duodenojejunal bypass. The first part of this surgery is similar to the traditional sleeve gastrectomy. It involves removal of part of the stomach and leaving a small gastric tube. Meanwhile, rearrangement of the small intestine allows food to enter distal small bowel without passage of remnant stomach, duodenum and proximal jejunum (150-200cm of small intestine in total), which affects the absorption rate. This surgery applies mostly to people with type 2 diabetes. It helps reduce food intake and appetite of the patients. Also, the food bypasses the duodenum and part of the jejunum which stimulates intestinal hormonal secretion and improves insulin secretion. This eventually helps with glycaemic control and weight reduction. With the complexity of this surgery, there are risks of leakage and bleeding during or after the surgery. Complication such as anaemia and osteoporosis may occur due to chronic vitamin deficiency. Meanwhile, more evidence on the long term efficacy of this surgery is needed.

5. Endoscopic weight loss procedures

Endoscopic weight loss procedures are not a permanent weight reduction treatment and provide only temporary control of body weight. These procedures are relatively safe compared to surgery but still carry certain risks.

Intragastric Balloon

The intragastric balloon is inserted through the mouth and down the oesophagus into the stomach, occupying 400-600ml of space, giving a sensation of satiety. Not all patients are suitable for this procedure. Contraindications include people who have stomach ulcers, hiatus hernia and previous stomach operation. The intragastric balloon is not a permanent treatment with a maximal treatment period of 6 months. Stomach ulcers may occur if the balloon remains in the stomach for too long. Balloon deflation may lead to bowel obstruction. After 6 months, the balloon is removed in the same way that it was placed, via the oesophagus and mouth. After the balloon is inserted, the body weight is expected to drop by around 10kg on average. Upon removal of the balloon, weight regain occurs. Therefore, adherence to a healthier lifestyle such a balanced diet and regular exercise is necessary in order to avoid weight regain after this procedure.

Endoscopic Gastric Plication (Endoscopic sleeve gastroplasty)

Gastric plication uses laparoscopic techniques to create large pleats in the stomach. This procedure does not involve the removal of stomach while still restricting the amount of food that the stomach can hold. However, this procedure is novel and more evidence on the long-term efficacy is needed.

Keynote: Bariatric surgery is not cosmetic surgery. Bariatric surgery facilitates weight reduction in order to reduce the risk of obesity-related health complications. People need to understand the risks associated with the surgery, be physically and mentally ready for the surgery, and to undergo a medical assessment before making the decision. All types of surgery require commitment to the instructions from doctors and dietitians. People need to make permanent health changes to their diet and exercise regularly to ensure successful weight management in the long-term.