If all of humanity was fair and sensible, no one would be falling ill from a lack of nutritious food or consumption of unhealthy foods that results in obesity. However, we still see undernutrition, obesity and micronutrient deficiencies (hidden hunger) as the three faces of malnutrition. The term overnutrition has been in vogue for describing overweight and obesity.
It is a term carried over from times when the world of human nutrition-focused mainly on adequacy of total calorie intake (energy) and not on nutrient quality. Instead of seeing obesity as a problem of excess calorie consumption, it is better understood as a measure of body fat and its patterns of distribution, with varying effects on health. Stunted children, who are the troubling picture of chronic undernutrition, have high levels of body fat and low levels of lean muscle mass, metabolically overlapping with those who are overweight and obese.
‘Overweight’ and ‘obesity’ are terms enmeshed in debates over criteria to be employed in different ethnic groups. Body mass index (BMI), a ratio of weight and height, is the conventional measure. It is expressed as weight in kilograms divided by a squared measure of height in metres. A BMI of less than 18 is labelled as underweight, between 18 to 25 as normal body weight, from 25 to 30 as overweight and over 30 as obese. These Western standards are still widely used for international comparisons. Overweight and obesity are associated with increasing health risk due to diabetes, heart attacks, stroke, cancer and many other diseases.
BMI, when used as an indicator of excess weight, is usually interpreted to be due to excess body fat (adipose tissue). It need not always be so, as a very muscular athlete can have a high BMI without high body adiposity. Even persons with high bone weight may be labelled as overweight without a high level of body fat. However, BMI has become the most commonly used measure for characterising overweight and obesity in individuals and populations, and a surrogate for undesirable levels of body fat.
Persons of Asian ethnicity, especially South Asians, have higher levels of body fat and associated metabolic risks at BMI levels lower than in Western populations. Recognising this, the WHO recommended lower public health and clinical thresholds for assessment of risk in Asians—a BMI of 23 for overweight and 27.5 for obesity.
The pattern of distribution of fat in the human body matters even more than total body fat or BMI. If fat is located more within the abdomen (not the abdominal wall), it carries greater danger. Fat distributed around the abdominal organs is associated with widespread inflammation in the body and also with a wide range of metabolic abnormalities in the composition and levels of blood fats, glucose and clotting mediators. About a third of the persons with diabetes in India have been reported to be thin, with central rather than general obesity. Early onset of hypertension, diabetes and heart disease in adulthood is a feature in India and other South Asian countries.
No genetic marker of high predictive value has yet been found. Patterns of imbalanced nutrition from early childhood are more likely to be responsible. Abdominal or central obesity has been conventionally measured by the ratio of the circumference of the waist to that of the hip. A high waist to hip ratio is usually associated with a male pattern of obesity (‘apple’ shape), while more fat around the hips is usually associated with a female pattern of obesity (‘pear’ shape). The former is metabolically dangerous and is associated with a wide variety of inflammatory and chronic degenerative diseases.
The latter is safer as it is not associated with similar metabolic abnormalities or inflammatory responses in the body. Even for the waist circumference and the waist to hip ratio, lower cut-offs have been recommended for Indians than used in Western populations, for better predicting the risk of cardiovascular disease and diabetes. Since hip measurement is often difficult, waist to height ratio has also emerged as a suitable surrogate measure of abdominal obesity.
A waist to height ratio of over 0.5 in older children and adults provides a reasonable clue to the presence of central or abdominal obesity. While early life influences seem to programme the body in the way it handles food intake in later life, our diet and physical activity patterns throughout will determine how that is expressed. A fibre-rich diet with fruit, vegetables and whole grain, and reducing sugar and refined carbohydrates while maintaining appropriate intake of protein and healthy fats will help us avoid all forms of obesity.
Physical activity is essential and resistance exercises are helpful in curtailing abdominal fat. The body tends to retain the same number of fat cells (adipocytes) throughout life. Whether we let them bloat with fat or keep them trim is up to us. Policy measures that make healthy foods affordable, unhealthy foods costlier and physical activity easy to undertake in community spaces are also needed.
DR K Srinath Reddy
Cardiologist, epidemiologist and President, PHFI
(The author wrote ‘Make Health in India: Reaching a Billion Plus’. Views are personal)