COMMENT
Obesity has become the 21st-century epidemic and, as such, continues to dominate the health scene. Finding the solution is hindered by the complexity of the issues, an incomplete understanding of genetic and environmental interactions, and unsatisfactory communication between the key players.
What do we know about this disease? Obesity is the excessive accumulation of body fat. Normally fat is widely distributed and has important health functions.
Convincing evidence indicates that obesity occurs when ingested energy exceeds that required for normal body function.
Eating patterns and lifestyle activities determine energy intake and expenditure and, therefore, the risk of obesity. Modern technology's large variety of food choices, labour-saving devices and sedentary lifestyle possibilities have nurtured environments in which obesity can flourish. We have yet to learn how to live in healthy harmony with the many options available.
Food provides energy (fuel) and the nutrients needed to keep the body functioning. Food energy comes from protein, carbohydrate and fat. There are many other food components that contribute little or no energy but have essential and beneficial health effects.
The resulting concentration of energy varies considerably from one food source to another. Thus, the concentration of energy in a food (energy density), together with food amount, is important in determining whether sufficient or excess energy is eaten.
Manufacturing permits modification of energy density while, more simply, by varying the serving size, the energy intake can be raised or lowered. Energy density balanced by serving size offers endless opportunities for dietary energy intake management, the maintenance of health and obesity prevention.
But what happens when there is persistent energy intake? Energy eaten in excess of what is required for maintaining body function and physical activity is converted in the liver to fatty acids to provide heat or be stored as fat deposits.
The site of these fat deposits is also an issue. Fat when deposited in the abdomen increasing abdominal girth becomes an active organ producing chemicals that increase the risk of heart disease, diabetes, some cancers and a number of other diseases.
Evidence indicates that excess fat deposited in other areas of the body, such as the thighs, does not appear to carry the same high risks as those associated with abdominal fat.
A concern is how best to measure obesity. Weight is simple but measures more than fat. Height is a partial measure of body size. The body mass index is a mathematical index combining weight and height which is simple and is used in large population studies and, as noted by epidemiologist Robert Scragg in his article on this page, gives a positive correlation with obesity and its associated diseases.
However, as Jeremy Irwin, of the Association of New Zealand Advertisers, has said, the body mass index is a crude measure of obesity. It might not be an accurate index of obesity in the individual. An index above 25 for adults needs careful interpretation.
So where do we stand in addressing the obesity issue? Increasingly, the food industry is recognising its key role in determining the food environment, but it needs help. The health industry holds some of the information but has not adequately shared this with industry.
It is not surprising, therefore, to find more people in the food and health industries recognising the need to form co-operative associations.
The consumer is the final determinant in tackling the obesity-producing food and lifestyle environments. Personal factors determine food consumption and lifestyle. Daily food intake is decided by appetite, satiety and desire.
Appetite is switched on by energy need and switched off by energy need satisfaction. Satisfaction (satiety) is a response to an adequate food volume stimulating the release of a small intestine hormone. Desire is the response to visual, smell or taste expectation that can overrule appetite and satiety. Once obesity has developed, these responses are modified to permit overeating.
The aim must be to prevent obesity. While our knowledge is incomplete, we have sufficient information to initiate prevention. Our ability to treat established obesity is less secure.
Proposals to change dietary patterns by regulation, legislation and litigation are not backed by evidence of efficacy or estimates of the risk of harmful consequences.
A truly healthy nation can be achieved by co-operation and the establishment of partnerships between public health promoters, the food industry, business, education and community services.
To ensure our success in the fight against obesity, we must work together on the solution rather than dwell on apportioning blame.
* Clifford Tasman-Jones is the honorary medical director of the Nutrition Foundation.
Herald Feature: Health
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