The human body contains certain proportion of fat for maintenance of body temperature and for reserve. However, too much fat will result in obesity. In particular, visceral fat (fat accumulated within the abdominal cavity or around internal organs), compared with subcutaneous fat (fat deposited under the skin), can lead to more serious health consequences. Central obesity is also a risk factor for many chronic diseases.

Definition of obesity

Body Mass Index (BMI) is a commonly used and internationally recognized objective index to assess whether an adult's weight is optimal. It is calculated as weight (in kilograms) divided by height (in metres) squared (i.e. weight divided by height twice). While the degree of fat accumulation within the abdominal cavity can be reflected by one's waist circumference.

• For Chinese adults in Hong Kong, a BMI from 23.0 kg/m² to less than 25.0 kg/m² is regarded overweight while a BMI greater than or equal to 25.0 kg/m² is considered obesity.
• For most Asian adults, central obesity is defined as having a waist circumference 90 centimetres (cm) (roughly 36 inches) or above, or a waist-to-hip ratio at 0.90 or above for men; and 80cm (roughly 32 inches) or above, or a waist-to-hip ratio of 0.85 or above for women.

Health consequences of obesity

Through certain biological mechanisms, obesity predisposes people to a wide range of chronic diseases, or even premature death. Chronic diseases associated with obesity include stroke, coronary heart disease, high blood pressure, certain cancers (including top common cancers in Hong Kong such as colorectal cancer, liver cancer, breast cancer, prostate cancer, etc), gallstones, diabetes mellitus, osteoarthritis of knees and varicose veins.

Causes of obesity

Energy from food provides fuels for basic metabolism and daily physical activities. Generally speaking, when the amount of energy absorbed is more than the expense, the extra energy will accumulate in the body in the form of fat and body weight will increase.

• Over-eating and frequent intake of food and drinks with high calorie, sugar, and fat content will lead to over-absorption of energy.
• Insufficient physical activities will decrease energy expense. If there is no adjustment in the diet, energy excess will result.
• In general, the risk of obesity increases with age.
• Hereditary factors, some diseases e.g. thyroid disease and side-effects of certain medications e.g. corticosteroids will also affect the body weight.

The principle of weight management

The principle of weight management is straightforward: to reduce energy intake and to increase energy expense. Adopting a healthy lifestyle – a healthy balanced diet, be physically active and to refrain from alcohol drinking, is the key to reduce the risk of obesity.

1. A healthy balance diet
   
   • Reduce as much as possible the intake of food with high calorie, sugar, and fat content e.g. deep fried food, pastries, desserts, meat with high fat content such as luncheon meat, pork belly, lap-mei, and animal skin; sugary drinks should also be avoided.
   • Eat at least 5 servings of fruit and vegetables per day and choose more whole grains as dietary fibres are more satiating which can prevent one from over-eating. They also help with bowel movement and prevent constipation. Soluble fibres bind with cholesterol-like substance which are then removed from the body. This helps to reduce cholesterol in the blood and stabilise blood sugar.
2. Be physically active
   
   • The World Health Organization recommends all adults to have at least 150-300 minutes of moderate aerobic physical activity per week; or at least 75 -150 minutes of vigorous aerobic physical activity per week.
   • To meet the goal , one can go for physical activities in shorter bouts (such as 10, 15 or 20 minutes) a few times a day.
   • Chair-time should be reduced. Small short walks can be incorporated into daily routines, for example, one can get off from public transport earlier and walk to the destination.
3. Refrain from alcohol drinking
   
   • Alcohol is extremely calorific but with no nutrition value. A can/small bottle of beer (330ml, 5% alcohol by volume) contains approximately 140 kilocalories. A glass of red wine (175 ml, 13% alcohol by volume) contains approximately 160 kilocalories.
   • Alcohol can affect carbohydrate metabolism in the liver and affect blood glucose level.

One should consult their family doctor and related healthcare professionals before taking weight management actions. Remember, this must be practised gradually and not in a rush. Patience and continuous effort are also the keys.

Misconceptions of weight management

1. Intermittent fasting: Currently there is yet to be conclusive evidence to support their benefits in older adults. There is also insufficient data about their potential side-effects.
2. Taking laxatives, diuretics or other“weight reducing agents”: laxatives and diuretics cannot reduce body fat. Furthermore, taking any medications without doctor's guidance could be harmful to health.
3. Avoiding rice and eating dishes only: Eating a balanced diet is vital in weight management. Grains should not be omitted in one's diet and on the contrary, they should take up the largest proportion in a diet to provide energy for body metabolism and physical activity. The fat content in dishes is generally higher than that in grains, and fat bears more calories than carbohydrates. Therefore, eating dishes only might result in even higher calorie intake.