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Obesity is a big medical concern. It is when there is an excessive amount of fat that causes medical problems. It is usually defined using the Body Mass Index, or BMI. BMI is a very crude calculation determined only by height and weight. In the USA, “overweight” is defined as a BMI over 25 kg/m2, and “obese” is over 30. This measurement is simplistic and does not take into account any nuance. For example, the CDC has found that the average American male is 5’9” and just under 200 lbs. This gives a BMI of 29.4, which is overweight. Arnold Scwartzenneger is 6’2”. At his peak performance, he weighed around 235 lbs, giving him a BMI of 30.2, which is classified as obese. Independent tests, however, have found that the average male has 28% body fat, whereas Arnold was at 8%. Nuances aside, BMI is an important calculation.

If the main measurement for obesity can give silly results, does that mean obesity is a made-up condition? Absolutely not. Obesity causes and makes several medical conditions worse. Four major mechanisms cause damage: inflammation, stress, fat, and weight. Inflammation can lead to diabetes, cancer, infertility, polycystic ovary syndrome (PCOS), and more. Stress is bad for many body systems, including mental health. Increased fat (also called lipids) can lead to liver damage. Stress and increased fat together can increase the chances of blood vessel damage, high blood pressure, heart attack, and stroke. Finally, the pressure of weight itself can degrade joints, squeeze organs, damage the kidneys, and constrict blood vessels.

So what causes obesity? At its simplest level, weight gain is caused by consuming more calories than you need. The reasons why some people can’t burn all of the calories can be vastly more complex. They can be broadly lumped into four categories: environmental, genetic, inflammatory, and brain-based mechanisms.

Environmental causes happen outside of the body. These include low exercise, a sedentary lifestyle, poor diet, and some medications. Eating disorders can be inherited, though the mechanism is unknown. The genetic factors of obesity are very complicated. There are over 200 genes that may affect obesity. To make matters worse, your body alters parts of the genetic code in response to environmental factors. This process, called epigenetics, complicates things a lot. On top of these two, inflammation is a big risk. Inflammation can lead to conditions such as metabolic syndrome and insulin resistance which affects how the body processes energy. Energy mismanagement on a systemic or cellular level is very hard to fight.

Brain-based mechanisms are complicated, but very powerful. We must first remember that some brain functions are specialized for a bygone time. Our brains are biased to ensure we are safe in times of scarcity, not times of plenty. This can lead to trouble in our modern era of readily available food. The brain can change on a physical level. When we routinely engage in dangerous behavior it is usually because parts of the brain have changed in an unhelpful way.

An example of brain changes can be found in systems around a hormone called Leptin. Leptin is secreted by fat cells and helps regulate our appetite. When fat stores run low, the brain detects low levels of leptin and kicks on your appetite – you get hungry. When you are full and fats are plentiful, there are abundant leptin molecules; your brain interprets this as full. When there is a change in this system – if the brain becomes resistant to leptin, for instance – trouble emerges. You might experience the feeling of hunger far after your body has eaten enough because your brain is misinterpreting the signals. The reward system can change dramatically in response to energy-dense foods. Rats exposed to tasty, fatty foods like cheesecake and bacon have reward system reductions similar to those seen with cocaine and heroin.

Obesity can spiral out of control, making it harder to reverse over time. Those four methods of creating damage: inflammation, stress, fat, and weight are all risk factors for obesity. Inflammation, for instance, can increase metabolic syndrome, a big driver of obesity. Obesity causes inflammation and might make metabolic syndrome worse. They can also disrupt the brain pathways that affect reward, inhibition, appetite, etc. Stress and changes to the reward pathway can lead to mental health trouble and worsen everything.

So what can be done? The best place to start is by targeting causes. It is necessary to keep a healthy environment where you are encouraged to exercise and limit calories. Other changes may need more assistance. Medications may be available or in trials to correct changes in gene expression, inflammatory responses, and specific hormones that affect the brain. Equally important is support from friends, family, and medical professionals. The struggle against obesity can quickly spiral out of control. Don’t be afraid to look for help with this condition.

Written By Benton Lowey-Ball, BS Behavioral Neuroscience

Sources:

Chooi, Y. C., Ding, C., & Magkos, F. (2019). The epidemiology of obesity. Metabolism, 92, 6-10. https://doi.org/10.1016/j.metabol.2018.09.005

Kenny, P. J. (2011). Reward mechanisms in obesity: new insights and future directions. Neuron, 69(4), 664-679. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3057652/

Obradovic, M., Sudar-Milovanovic, E., Soskic, S., Essack, M., Arya, S., Stewart, A. J., … & Isenovic, E. R. (2021). Leptin and obesity: role and clinical implication. Frontiers in Endocrinology, 12, 585887. https://www.frontiersin.org/articles/10.3389/fendo.2021.585887/full

St‐Onge, M. P. (2010). Are normal‐weight Americans over‐fat?. Obesity, 18(11), 2067-2068. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3837418/

Upadhyay, J., Farr, O., Perakakis, N., Ghaly, W., & Mantzoros, C. (2018). Obesity as a disease. Medical Clinics, 102(1), 13-33 .http://www.medicinainterna.net.pe/sites/default/files/Obesidad_como_enfermedad.pdf