Obesity

I came out of medical school at the end of the 1990s with a relatively limited understanding of the causes of obesity. I remember as a junior doctor explaining to my patients that obesity was a risk factor for heart attacks, strokes and diabetes (this is true) and that obesity was simply a mismatch between calories taken in and those expended (I now know this is false), and that by doing more exercise and eating fewer calories one could lose weight (it’s really not as simple as this).

As I became more experienced as a doctor, I started to question this simple view of obesity because the evidence in front of me told another story. So many of my motivated, informed and hard-working patients were failing to lose weight effectively despite following all the advice given to them - so what was going on? The obesity epidemic began in the 1980s, and with it the rise in ‘diseases of modern life’: high blood pressure, heart disease, stroke, diabetes and many cancers. Humans didn’t change their nature or physiology overnight so it’s clear that something happened in our environment to cause this – and what happened in the mid-1970s was a shocking disaster in public health policy. On reviewing the evidence, it was decreed that fat, especially saturated animal fat, caused people to be fat and sick - when in fact the main culprit was sugar, but the evidence for this was hidden. 

In response to this public health policy food companies made lots of ‘healthy’ food labelled ‘low fat’ that was packed with sugar, salt and vegetable polyunsaturated fats. So at the end of the 1970s we began eating increasing amounts of ultra-processed foods (UPF). At present on average 57% of the food we eat in the UK is UPF. Some UPF foods are obvious (eg a chocolate bar) some less so (like mass-produced bread or fruit yoghurts). These UPF foods are often high in calories, but they are also vastly changed from real food, with fibre removed and sugar added (to make it taste nicer), omega 6 levels raised (in large part because of the vegetable oils used), omega 3 lowered, and salt added (to prolong shelf life). These changes mean that UPF foods make the body react in very different ways compared to unprocessed food. They cause a much larger rush of glucose into the blood, and the body responds with a large spike of insulin. In the short term this causes us to be hungry again much sooner and to eat more of the lovely, high calorie UPF food. In the long term it causes blunting of our body’s sensors to detect when we have eaten enough and what to do with our extra calories.

This environment of UPF foods, via the hormonal feedback systems in the body, gradually resets what the body thinks its weight should be so you put on weight and it proves incredibly difficult to lose it and keep it off. Many things can have an impact on our ‘set weight’: stress seems to increase it (we often put weight on when stressed due to the comfort eating urge most of us have experienced); shift work increases it; but exercise seems to decrease it and helps with sustained weight loss. Interestingly, dieting and significantly restricting calories increases our body’s weight set point, which is why many of us have experienced losing weight on diets, then when we eat normally again, we put all the weight back on, and then some more to reach the body’s new raised set point – so we end up heavier.

I hope that governments will take action on this soon – but with hugely powerful food companies and pharmaceutical giants trying to slow this change (selling cheap UHP food is profitable and if people become ill from eating it, they require medicines, which are also profitable) it may be some years before we see useful change. There isn’t an easy answer while our environment is working against us like this, but I would urge everyone to cook and eat unprocessed food wherever possible, and also to look at the available research – and keep interested and up-to-date, because our understanding of the topic is increasing all the time. 

You could listen to the ZOE Science & Nutrition podcast and there are also some great books on this topic, some are scientific, but accessible ones include: Fat Chance by Dr Robert Lustig; Why we eat (too much) by Dr Andrew Jenkinson; Ultra-Processed People by Dr Chris Van Tulleken; Food for Life by Dr Tim Spector. Useful resources when thinking about dietary changes are the Freshwell Low Carb Project app and diet books, Open Food Facts app, or phcuk.org/sugar which shows how common foods affect blood glucose.