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It’s that time of year again. Christmas is over and the vast number of mince pies and Christmas puddings I’ve consumed are sitting uncomfortably around my waistband. All that’s left is for the endless stream of grand New Years’ resolutions, promising a healthier, fitter and slightly lighter new year to start the annual assault on my facebook newsfeed.
But despite this annual clean up act, we as nation are getting fatter. Dame Sally Davies the Chief Medical Officer even went as far as to call female obesity a ‘national risk’ in December.  With 36 % of women 16-24 and 50 % of women 25-34 classified as obese I’m inclined to agree.  However, this rather weighty problem is by no means limited to women, in fact 61.7 % of all adults are overweight or obese. 
Obesity is most commonly measured by the Body Mass Index (BMI), where a person’s weight in kilograms is divided by the square of their height in metres. Whilst it’s a relatively crude method of defining obesity on an individual level, as it is unable to differentiate between weight as muscle and weight a fat, it’s a useful method for assessing the levels of obesity within populations. Those scoring 18.5-24.9 are considered to be a healthy weight, whilst people obtaining values between 25 and 29.9 are overweight. Meanwhile those with a BMI exceeding 30 are categorised as obese and are at risk of developing many life limiting diseases, such as type 2 diabetes, heart disease and numerous bowel and gastro related cancers. Furthermore, recent reports have indicated that obesity can lower the life expectancy by approximately 8 years, and that obesity associated conditions further lower the quality of life of obesity sufferers by another 11-19 years. 
Yes, it’s serious stuff! Yet recent scientific studies have highlighted that it’s not just a matter of eating a few less mince pies and foregoing the extra helping of brandy butter – but that the taste of fatty and sugary foods is in actual fact fundamentally changing the biochemistry of our bodies.
Over the past several hundred thousand years our bodies have honed down the key survival skills fairly well – regulating our food intake being one of them. At the centre of this regulation is the hormone leptin, which regulates our appetite by activating receptors in an area of the brain called the hypothalamus. When leptin levels are low our bodies respond by feeling hungry. When we are full leptin levels increase instructing us to stop eating. 
However recent studies have shown that receptors in the ventral tegmental area of the brain (VTA) are also able to detect leptin. This area of the brain contains dopamine neurons and forms an important role in the brains reward system. Our body’s reward system, triggered by actions such as eating, exercise, or sex is supposed to promote good behaviours, as a way of encouraging us to repeat them. High calorie diets, or foods with a high sugar or fat content chronically overload this natural reward system, which in turn leads the body to produce fewer dopamine receptors. The downregulation of dopamine receptors means more stimulant or sugary foods are then required in order to elicit the same response. This phenomena, known as gaining ‘tolerance’, is observed during all addictions, begging the question of whether obesity is actually an addiction to food? [5, 6]
So how exactly does this shift in dopamine sensitivity impact our ability to shed those extra pounds? As obese people are leptin and dopamine insensitive, they find it harder to resist food cravings. Combine this with a crash diet, where leptin levels drop further in an attempt to remind the person to eat, and you are left with substantially lower leptin levels than usual. Not only does an obese dieter have to try and overcome their bodies hunger signals but they also have to resist cravings from a lack of dopamine.
Furthermore, studies show obese rats reared on high calorific foods find it stressful returning to less densely calorific diets. Obese rats exhibited five times the levels of corticotropin releasing factor (CRF), a neuropeptide involved in activating the stress response, during the period they were denied the high calorific diet. The study showed that on return to the high calorie diet, the rats CRF levels returned to normal, though the rats themselves continued to overeat more than they had before. This finding suggests that not only is weight loss a considerable physiological strain, but a psychological one too, and perhaps explains why frequent dieters may find it increasingly difficult to lose weight. 
The most alarmingly part however, is that these changes in our biochemistry are not only impacting those struggling to manage their daily intake, but those of the future generations too. Offspring of obese mothers experience a higher frequency of obesity throughout their own lives and also display a greater tendency towards addictive behaviours.
The message is clear - our fondness for all things sweet and calorie laden is paving our way to a more obese society, with health complications galore; and as fatty, sugary foods become more available to the world we are unable to resist them. If we are to reverse the nation’s growing belly’s we are going to need more to spur us on than a few empty New Year resolutions and discounted gym membership offers come January.
As little as three decades ago the state was still choosing to largely ignore the impact of smoking. How long will it be before obesity is taken seriously?