Obesity metabolism (extreme obesity)

Last updated date: 09-Jan-2023

Originally Written in English

Obesity metabolism (extreme obesity)

Obesity metabolism (extreme obesity)


When calorie intake exceeds energy expenditure, body fat mass rises. Obesity will come from a favorable energy balance in the long run. Obesity incidence has skyrocketed globally, posing a severe danger to human health. As a result, understanding the pathophysiology of obesity is critical for developing innovative preventive and treatment measures.


What is Obesity?


Obesity or overweight refers to carrying too much weight and body fat. Obesity places you in the greatest weight range, over what is deemed healthy. Overweight denotes that your body weight is outside of a healthy range, although it is not as severe as obesity.

In Australia, two out of every three adults and one out of every four children are fat or overweight. Experts anticipate that more than three-quarters of Australian individuals will be fat or overweight by 2025.

Obesity is a touchy subject. Obesity is more than simply a cosmetic issue; it raises a person's risk of heart disease, type 2 diabetes, and other severe illnesses. Adopting good eating habits and engaging in regular exercise can help you control your weight. With some situations, your doctor may also suggest medications or surgery to aid in weight loss.


What are the signs of obesity?

Excess body fat, as measured by BMI, is the most apparent indication of obesity. Obesity is defined as a BMI of 30 or above, whereas overweight is defined as a BMI between 25 and 30. You may determine your BMI using an adult calculator. However, typical BMI estimates can miscalculate a healthy weight for those under the age of 18, pregnant women, and people of particular ethnicities.


What causes obesity?

Obesity develops gradually in most people by consuming more energy than your body requires over time. Food and beverages include energy, which your body expends, particularly during physical exercise. The average adult requires 8700kJ per day, and any excess energy is stored as body fat. As a result, overeating and drinking without increased exercise leads to weight gain over time.


Controllable factors

Obesity develops gradually from poor diet and lifestyle choices, such as:

  • Eating junk food frequently — fast food meals, cakes and pastries, sweets, processed meats and sugary drinks are loaded with kilojules.
  • Drinking too much alcohol , which contains a lot of kilojoules with no nutritional benefits.
  • Avoiding physical activity — only half of Australians do enough physical activity for good health.

There is rarely a single reason why someone chooses to eat or drink excessively. People may consume more kilojoules than they require due to stress, bad mood, lack of desire, shifting emotions, or a lack of access to healthy choices.

Obesity can also result from other factors, such as:

  • Your family history — the habits you grew up with and the genes you inherited from your parents.
  • Your surroundings — what kinds of food are available and in what portions, where you work and sleep.
  • Your metabolism — how efficiently your body turns food into energy.
  • Certain medical conditions that cause weight gain, such as hypothyroidism.
  • Certain medications can cause weight gain as a side effect, such as antipsychotic medications.

Whatever the cause of your obesity, your doctor can assist you in losing weight and improving your overall health.


What is Obesity metabolism?

Obesity metabolism

Obesity and metabolic disorders are developing as the epidemics of the twenty-first century, fueled by an increasingly sedentary lifestyle and bad food habits. Obesity increases "all cause" mortality by being a risk factor for a variety of illnesses such as stroke, cardiovascular disease, type 2 diabetes (T2D), liver disease, and various malignancies. Obesity is a major and leading cause of disease burden worldwide, and it is increasingly being recognized and treated as a chronic disease.

Hormones are chemical messengers that govern bodily functions. They are one of the factors that contribute to obesity. Our hunger, metabolism (the rate at which our body consumes kilojoules for energy), and body fat distribution are all influenced by the hormones leptin and insulin, as well as sex hormones and growth hormone. Obese people have higher amounts of these hormones, which promote improper metabolism and the storage of body fat.

The endocrine system is a network of glands that secretes hormones into our circulation. The endocrine system collaborates with the neurological and immunological systems to assist our bodies cope with various events and pressures. Hormone excesses or deficiencies can contribute to obesity, while obesity can lead to hormonal changes.


Obesity and Leptin

Fat cells create leptin, which is then released into our circulation. Leptin suppresses a person's appetite by working on certain areas of the brain that control the desire to eat. It also appears to affect how the body controls its fat stores.

Because leptin is created by fat, obese persons have greater leptin levels than normal weight people. Obese persons, although having larger amounts of this appetite-reducing hormone, are less sensitive to its effects and, as a result, do not feel full during and after a meal. Ongoing study is looking at why leptin signals aren't reaching the brain in obese persons.


Obesity and Insulin

Insulin, a hormone generated by the pancreas, is essential for glucose control and fat metabolism. Insulin promotes the absorption of glucose (sugar) from the blood in tissues such as muscles, the liver, and fat. This is a critical mechanism for ensuring that energy is supplied for daily functioning and that appropriate levels of circulating glucose are maintained.

Insulin signals are occasionally lost in obese people, and tissues are no longer able to manage glucose levels. This can result in type II diabetes and the metabolic syndrome.


Obesity and Sex Hormones

The distribution of body fat contributes significantly to the development of obesity-related illnesses such as heart disease, stroke, and several kinds of arthritis. Fat deposited around our belly has a greater risk of disease than fat stored on our bottom, hips, and thighs. Estrogens and androgens appear to have a role in determining body fat distribution. Estrogens are sex hormones produced by premenopausal women's ovaries. They are in charge of triggering ovulation during each menstrual cycle.

Men and postmenopausal women generate less estrogen in their testicles or ovaries. Instead, the majority of their estrogen is created in their body fat, but in considerably smaller levels than in pre-menopausal ovaries. Androgens are generated in abundance in the testes of younger males. These levels steadily decline as a guy ages.

Variations in sex hormone levels in both men and women with age are linked to changes in body fat distribution. Women of reproductive age prefer to store fat in their lower body ('pear-shaped,' whereas older men and postmenopausal women tend to store fat around their belly ('apple-shaped,'). Postmenopausal women who use estrogen pills do not gain weight around their midsection. Excessive weight gain has also been linked to a shortage of estrogen in animal studies.


Obesity and growth hormone

The pituitary gland in our brain generates growth hormone, which impacts height and aids in the development of bone and muscle. Growth hormone has an impact on metabolism as well (the rate at which we burn kilojoules for energy). Obese persons have lower amounts of growth hormone than people of normal weight, according to researchers.


Inflammatory factors and obesity

Obesity is also linked to low-grade chronic inflammation in adipose tissue. Excessive fat storage causes stress responses inside fat cells, which results in the release of pro-inflammatory substances from fat cells and immune cells within the adipose (fat) tissue.


Obesity hormones as a risk factor for disease

Obesity is linked to an increased risk of a variety of disorders, including cardiovascular disease, stroke, and various forms of cancer, as well as shortened longevity (life span) and worse quality of life. For example, greater estrogen synthesis in the fat of obese older women is related with an increased risk of breast cancer, demonstrating that the source of oestrogen production is crucial.


Behavior and obesity hormones

Obese people have hormone levels that promote the growth of body fat. Overeating and a lack of regular exercise appear to'reset' the systems that govern hunger and body fat distribution, making a person biologically more inclined to acquire weight. Because the body is always attempting to maintain equilibrium, it is resistant to any short-term disturbances such as crash diets.

Several studies have found that following a low-calorie diet, a person's blood leptin level declines. Lower leptin levels can cause an increase in hunger and a slowing of metabolism. This may help to explain why crash dieters frequently gain back the weight they lost. Leptin treatment may one day help dieters maintain their weight reduction over time, but more study is needed before this becomes a reality.

Long-term behavior adjustments, such as healthy diet and frequent exercise, have been shown to re-train the body to lose extra body fat and keep it off. Weight reduction as a consequence of a good diet and exercise or bariatric surgery also leads to better insulin resistance, lower inflammation, and favorable regulation of obesity hormones, according to research. Weight loss is also linked to a lower chance of getting heart disease, stroke, type II diabetes, and some malignancies.


Effect of Obesity on Carbohydrate Metabolism

Effect of Obesity on Carbohydrate Metabolism

Insulin works to reduce blood glucose levels by suppressing hepatic glucose synthesis and increasing glucose absorption into muscle and adipose tissue via GLUT4. Muscle has long been thought to be the primary location of insulin-stimulated glucose absorption in vivo, with adipose tissue accounting for a small portion of total body glucose disposal. Various transgenic experiments, on the other hand, have suggested the potential of a higher role for glucose absorption into fat in systemic glucose homeostasis.

Overexpression of GLUT4 in fat tissue improves whole-body insulin sensitivity and glucose tolerance, but knocking down GLUT4 in fat tissue leads in insulin resistance comparable to that found with muscle-specific GLUT4 deletion. Downregulation of GLUT4 in all kinds of obesity is a primary factor leading to decreased insulin-stimulated glucose transport in adipocytes. However, GLUT4 expression is normal in the skeletal muscle of obese adults. It has also been proposed that poor glucose transport is caused by GLUT4-containing vesicles failing to translocate, dock, or fuse with the plasma membrane.

Obesity causes a decrease in glucose elimination in adipose tissue. Obesity has been linked to the development of hyperglycemia, hyperlipemia, hyperinsulinemia, and insulin resistance. FFA, leptin, and TNF-, all of which are produced by adipose tissue, are known to have an indirect effect on glucose homeostasis. There are undoubtedly more chemicals from adipose tissue that impact systemic metabolism that have yet to be found.


Effect of Obesity on Lipid Metabolism

Lipid Metabolism

Obesity is related with increased adipose tissue basal lipolysis and enhanced circulating FFAs. In humans, acute-phase serum amyloid A (SAA), a lipolytic adipokine, increases basal lipolysis. Lipolysis is thought to be an autocrine feedback process via which increased SAA production from larger adipocytes A into the circulation contributes to insulin resistance. The SAA directly induce lipolysis via the CLA-1 and extracellular signal-regulated kinase signaling pathways. Alternatively, enhanced lipolysis by SAA might be indirect, i.e. by activation of lipolytic cytokines such as IL-6 and TNF

Another metabolic indicator that is most influenced in obesity is plasma triglyceride (TG) levels. It has been proposed that tissue resistance to insulin-mediated glucose absorption enhances the rate of very low density lipoprotein (VLDL) TG synthesis and results in endogenous hypertriglyceridemia. Obesity reduces Lipoprotein lipase-mediated lipolysis of chylomicron-TG and inhibits hormone-sensitive lipase-mediated lipolysis in adipose tissue ineffectively.

Obesity is associated with postprandial lipemia and higher plasma FA levels. It is believed that excess fatty acid availability early in the postprandial phase (when it is generally reduced by insulin) influences glucose absorption by up to 50%. SAA also has an immediate impact on cholesterol metabolism. It is the apoprotein of high-density lipoprotein and is an apolipoprotein by nature (HDL). 

SAA-HDL interaction may degrade HDL's function as an anti-atherogenic molecule and facilitate its breakdown. Obesity-related increases in adipose tissue-derived SAA may represent a relationship between obesity, low HDL, and an increased risk of coronary artery disease.


Effect of Obesity on Protein Metabolism

Protein Metabolism

Human obesity is well known to be associated with problems in both glucose and lipid metabolism. However, whether protein metabolism is similarly disrupted in overweight people is debatable. Some researchers have reported that moderate obesity and differences in body fat distribution are associated with abnormalities in protein metabolism, hypothesizing that moderate obesity is associated with increased proteolysis, an increased rate of basal leucine turnover, and the impairment of insulin's antiproteolytic action, whereas others have found comparable rates of basal leucine turnover in nonobese and obese subjects.


Role of Obesity in Inflammation

Obesity in Inflammation

Adipokines are proteins generated from adipose tissue that have been linked to the pathophysiology of chronic inflammation in obesity. The discovery of resident macrophages in adipose tissue has a significant influence on the research of adipose tissue on inflammation. The chemokines released by adipocytes, which attract resident macrophages, might be one of the processes causing macrophage infiltration into adipose tissue. In reaction to adipocyte necrosis, macrophages enter adipose tissue as part of a scavenger role.

Obese people have an increased amount of macrophages in their adipose tissue, and when activated, these macrophages release a variety of cytokines, including TNF-, IL-6, and IL-1. The majority of the tissue TNF- and IL-6 are produced by adipose tissue-resident macrophages.


How is Obesity Diagnosed?

Obesity Diagnosed

Body mass index

Your doctor will measure your height and weight to calculate your BMI, and to assess whether you are obese or overweight.

For most adults:

  • a BMI between 18.5 and 24.9 is considered healthy
  • a BMI between 25 and 29.9 is considered overweight
  • a BMI of 30 and above is considered obese

A BMI assessment may be less accurate in certain groups of people due to inherent differences in muscle and fat mass proportions. Athletes with a lot of muscular mass, for example, may be classified as obese based on their BMI when they are actually a healthy weight.


Waist circumference

In order to determine your weight, your doctor may additionally measure your waist circumference. Obesity-related health issues, such as type 2 diabetes, heart disease, and some malignancies, are more likely if you have a waist circumference of 94cm or more (for males) or 80cm or more (for non-pregnant women).


Other tests

To estimate your risk of additional obesity-related diseases, your doctor may also examine your blood pressure, blood glucose (sugar), and lipid (cholesterol) levels.


How is Obesity managed?


Unfortunately, there is no such thing as a "quick fix" cure for obesity. A calorie-controlled diet combined with regular exercise can usually help you lose weight and feel better. It's also critical to have a cheerful attitude.


Reducing your kilojoule intake

Changing your diet to generate an energy deficit is one strategy to lose weight. You may achieve this by replacing high-energy foods like fast food, processed foods, sugary beverages, and alcohol with healthier options like vegetables and fruit. Be wary of diets that encourage harmful behaviors or altogether exclude particular meals. When considering a diet change, it may be beneficial to consult with a dietician about a customized dietary plan.


Increasing physical activity

To lose weight, combine dietary modifications with at least 30 minutes of moderate-intensity physical exercise each day – anything that involves more effort than normal, such as brisk walking, swimming, or playing tennis.

Many physical activities, such as using the stairs instead of the elevator, physically playing with your children, utilizing public transportation, or cycling, may be included into your daily routine. Joining an exercise club or sports team for inspiration and support may be beneficial.

Research shows that:

  • Doing any physical activity is better than doing none;
  • Incorporating daily physical activity is more effective than only once or twice a week
  • Strength or resistance training exercise (exercising with weights) at least twice a week is particularly helpful for your metabolism (how fast you burn energy) and bone health.


Supporting your weight loss

If you've previously struggled to lose weight, seeing a therapist or psychologist who can assist you with long-term improvements may be beneficial. Cognitive-behavioral therapy, for example, might make it easier to lose weight by training you to recognize when and why you eat, as well as how to modify harmful attitudes or thinking habits. Your doctor can recommend you to a therapist or counselor.


Weight-loss medicines

In Australia, prescription weight loss medications are accessible. However, it is critical to combine these with calorie restriction and increased physical exercise. Some medications work by decreasing the amount of fat absorbed from food, while others help you feel less hungry. Weight loss medications have adverse effects and are not appropriate for everyone. Before beginning a weight-loss medication, consult with your doctor or pharmacist to ensure that it is appropriate for you.


Weight-loss surgery

By altering the way the body digests and absorbs food, bariatric surgery can help some people lose weight. When contemplating weight reduction surgery, your doctor will examine factors such as your BMI, whether you've tried other weight loss treatments, and how much obesity interferes with your everyday activities.


Complementary therapies and supplements

There are several alternative therapies and weight loss medicines that are touted to perform miracles. However, they should not be used in place of tried and true procedures.



Obesity is thought to be induced by an increase in calorie intake without an increase in energy utilization. Obesity leads to a worse quality of life, mostly owing to the inability to move freely as a result of being overweight.