Weight management is a holistic approach that takes time.
"Rapid weight loss could induce gallstone formation and increase the risk of osteoporosis and nutritional deficiencies," said Dr Liu Han Ping, an aesthetic doctor at Thomson Well Women Clinic.
To maintain a healthy body long term typically requires a change in eating habits, aerobic exercise and social support, he said.
Apart from the body mass index (BMI), the waist-to-hip ratio (WHR) can be used to see if one is overweight, rather than the collarbone challenge, said Dr Liu.
"The collarbone challenge does not accurately estimate fat distribution in the body. WHR is a better index," he said.
He noted that men whose WHR exceeds 1.0 have been associated with an increased health risk; for women, the ratio is 0.8.
The body fat percentage test is another gauge. It uses skinfold measurements or the body adiposity index, which evaluates body composition based on height and waist circumference, said Dr Christina Low, a general practitioner at Singapore Medical Group.
"However, there is no single test that should be used to judge your health. Until such a test becomes available, BMI could still prove useful," she said.
However, BMI should be combined with a comprehensive evaluation of the patient's medical history and lifestyle habits in order to provide a better indication of his health, she noted.
Maintaining a healthy weight can help a person to avoid or control many diseases and ailments, doctors said.