Is obesity a disease?

Obesity affects an increasing number of people in the UK, and is clearly linked to conditions such as diabetes and heart disease – but is it a disease in itself? It’s a big debate, so we got the perspective of leading bariatric surgeon, Mr Ahmed Ahmed, who explains the role of genetics in our ability to lose weight.

What is obesity?

Obesity is defined as an excess accumulation of fat, and is diagnosed when a patient presents with a body mass index (BMI) of 30 or over.

At this stage, there is a much greater risk of developing long-term health problems such as hypertension, type 2 diabetes, osteoarthritis, and asthma. Obesity is also linked to bowel cancer, breast cancer, womb and ovarian cancer.

There is also an association between the level of obesity and the amount that it shortens your life, for example a 20 year old obese man with BMI 45 will lose approximately 14 years of life.

On the whole, obesity could be described as a chronic condition with serious consequences in terms of morbidity and mortality.

What causes obesity?

Although obesity can be caused by medication, such as antidepressants, or diseases such as hypothyroidism, polycystic ovarian syndrome and Cushing’s syndrome, the majority of people are “predisposed” to obesity through their genes. We’ve identified about 100 genes that play a role in our metabolism, when we feel hungry and when we feel full, and the rate at which we burn calories.

There is increasing evidence that these genes drive behaviours that result in a calorific surplus, from overeating and/or not getting enough exercise. Clearly there is a debate over to what extent this is an individual or societal problem and this is too broad to discuss here, but it doesn’t necessarily affect whether or not we regard obesity as a disease. After all, even though smoking is the leading cause of lung cancer, we still class lung cancer as a disease.

Why does obesity need specialist treatment?

One of the things that marks out a disease is the necessary involvement of a health professional, or some form of medical treatment. In the case of obesity, it is clear that medical treatment is necessary, because self-management through diet and exercise is rarely successful in the obese state.

The fact is that our bodies are strongly resistant to losing weight. When we try to diet and cut the amounts of calories we are taking, the body adapts quickly to function on fewer calories. The kind of diets that result in rapid weight loss are impossible to carry on in the long term – the hunger drive is too strong. When you stop dieting and resume normal eating patterns, your metabolism stays dampened down.

As a result, the amount of weight loss an individual with obesity can achieve on their own is very limited, and rarely enough to declassify them as obese. In the majority of cases, people with obesity who diet and subsequently lose some weight, will eventually not only return to their previous weight, but gain further weight (the so called "yo-yo effect" of dieting).

What treatment does work?

The only treatment which is scientifically proven to achieve long-term, significant weight loss in obese patients is bariatric surgery.

Bariatric surgery doesn’t just achieve a reduction in the size of the stomach. We’ve found that patients who have received bariatric surgery report lower levels of hunger, and tend to burn calories at a faster rate. Why this happens remains a mystery – although numerous ideas have been suggested – but the net effect is that most patients maintain their weight loss more than 20 years after the operation.

Does this mean that current medical advice is wrong?

Not at all – physical exercise and a healthy diet are important for everyone, not just because of the weight loss achieved but for other useful effects on health and wellbeing.

Furthermore, NICE guidelines already recommend specialist treatment for patients with a BMI over 30 or over 27 for those of Asian descent.

The main problem we have is in preventing obesity – it now affects 1 in 4 adults in the UK. However, given that so many of us lead sedentary working lives, so few of us have the time or energy to walk to the local greengrocer/butcher/fishmonger, and it’s often difficult to find time to make fresh, healthy meals for ourselves, the real question is what sort of societal changes we are prepared to accept to tackle the obesity epidemic.