The physiology of weight regulation
Obesity is a major global health problem, and for a long time, it has been perceived as being caused by self-imposed bad habits. There are several mechanisms involved in body weight regulation in humans including genetic, physiological, and behavioral factors.
It was not until 2013 that the American Medical Association deemed that obesity was, “a disease requiring a range of medical interventions to advance obesity treatment and prevention.”
Although dietary modifications and increased physical activity are both logical and safe interventions to promote weight loss, they often are not enough to support long-term maintenance of reduced weight. Over time, many individuals regain weight they had previously lost.
There are several factors at play, which complicate weight loss and make it more difficult to both achieve and sustain.
Hormones
Body weight is regulated by a complex neuro-hormonal system. Both the brain and hormones are involved.
The hypothalamus, specifically, is involved in weight regulation. This part of the brain receives information from the gastrointestinal tract, pancreas, and adipose tissue through hormonal signals.
Some hormones can affect appetite. Our bodies have orexigenic hormones, which drive weight gain. An example is ghrelin, which is known as the “hunger hormone.” Ghrelin stimulates appetite and promotes fat storage.
Our bodies also have anorexigenic hormones, which drive weight loss. Leptin is an anorexigenic hormone that is known to inhibit hunger, which decreases fat storage.
Hormonal changes can arise following successful weight loss. These changes have been found to favor weight regain by increasing appetite and promoting fat storage. Increased levels of ghrelin and decreased levels of leptin have been noted.
Additionally, one study following fifty overweight and obese individuals found that this significant hormonal imbalance was still present one full year after their initial diet-induced weight loss. This suggests that the change in appetite regulating hormones is not short-term.
Decreased thermogenesis
Weight loss has been found to result in adaptive thermogenesis. The triggering effect of significant weight loss or food deprivation can cause the body to focus on conserving energy by reducing energy expenditure. It is also known as “the starvation response.”
This survival mechanism is designed to prevent starvation, but it also makes weight loss more difficult to sustain.
You might be familiar with “The Biggest Loser” competition. Approximately 15 participants in this competition were studied. It was found that their resting metabolic rate was about five hundred calories lower than expected per day based on their body composition. Additionally, the individuals who exhibited the most notable weight loss, had the greatest slowing of resting metabolic rate.
Obesogenic environment
Obesogenic is defined as “tending to cause obesity.” Our environment presents the opportunity for over-indulgence. There is intense marketing of high calorie foods and expanding portion sizes. Increased availability and low cost of these energy-dense food options also contribute to the obesity epidemic.
Stress is also a factor. Living in a fast-paced, high stress society can stimulate compensatory food intake.
Our environment makes it even more difficult for people to maintain a healthy body weight through well balanced eating and physical activity, especially if an individual is employed at a sedentary job.
Stress
Cortisol is the body’s main stress hormone. Not only does it fuel our “fight or flight” response, but it also regulates blood pressure, increases blood sugar, and manages how the body uses carbohydrates, fat and protein.
Cortisol is important for our health, but too high a level can lead to weight gain as it can increase appetite and promote overeating.
When under chronic stress, it can also be difficult to maintain healthy eating habits. Some individuals tend to resort to higher calorie, indulgent foods for comfort.
Circadian rhythm
Circadian rhythm refers to the body’s 24-hour clock, which regulates the sleep/wake cycle, often in response to light and darkness. Some research has suggested that eating late at night, or outside of typical meal times, can desynchronize this cycle. Additionally, research has noted a link between incidence of obesity and sleep debt.
Circadian disturbances have been associated with metabolic dysfunction, alterations in eating behavior and weight gain.
Bariatric surgery and obesity medicine
Reseting an individual’s physiology may be the most effective way to support sustainable weight loss, as compensatory physiological adaptations favor weight regain.
Anti-obesity medications, and also bariatric surgery, may help to do so. Some research is indicating that these approaches to weight loss offer the best success long term.
For example, the gastric bypass surgery has been noted as eliciting “profound physiological and metabolic changes” due to surgical manipulation. Positive clinical outcomes of bariatric surgery have been notable.
The usage of weight loss medications is also on the horizon and already being utilized by some. Practitioners are beginning to think of obesity as a disease, similarly to diabetes or hypertension.
When an individual is diagnosed with diabetes, it is typical for a practitioner to prescribe a medication to help lower blood sugar. Similarly, obesity is a disease with contributing physiological components.
Dietary and behavior changes are recommended for those with obesity, just like those with diabetes. And perhaps with time, it will also become common for practitioners to consider medications to treat obesity as well.
Conclusion
In the United States in 2020, the adult obesity rate was as high as 42.4%. Worldwide, obesity has nearly tripled since 1975.
This disease not only decreases quality of life, but it can also predispose individuals to other co-morbidities, such as type II diabetes, heart disease, stroke, cancer and arthritis. With obesity, also comes a shortened life expectancy.
According to a peer reviewed article published by the American Diabetes Association in 2017, about 50% of weight variance is determined by genetics and the other 50% by environmental factors, such as decreased physical activity and the consumption of high calorie foods.
Hormonal, metabolic, and neurological factors are all involved and have been found to support weight regain.
Hopefully, with improved understanding of the physiology of weight regulation, our medical field will be able to develop more effective strategies to support sustainable weight loss.
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