Hunger and Obesity
PKGhatak, MD
One cannot escape from the fact that the present generation is getting heavier and fatter, despite cable channels broadcasting continuously healthy cooking, diet, and exercise, the print media are not far behind.
Why then is the opposite happening!
Maybe we are asking the wrong questions. We should be asking what makes us feel hungry.
Hunger is a sensation registered in the brain as a strong desire for food. As we fill up our stomachs with food and drinks, the hunger goes away and again returns after an interval.
The nerve center for hunger, the Appetite Center, is located in the Hypothalamus. The stomach and small intestine are connected to the appetite center. The hypothalamus, in turn, is connected with other parts of the brain, and the input reaches the conscious level in the cerebral cortex.
A full stomach sends signals to the brain through the vagus nerve. The appetite shuts down. Alcohol speeds up stomach emptying, and fat delays emptying.
In starved conditions, the fat cells provide needed energy. Eating extra food makes adipocytes bulge with fat. Leptin, a hormone, decreases appetite and increases energy expenditure (EEx). Adipocytes also produce blood pressure regulating Angiotensinogen, a vascular protective protein called Adiponectin, a blood clotting inhibitor known as Plasminogen activator inhibitor 1, a complement called Adiposin or factor D, and cytokines - Interleukin IL6 and Tumor necrosis factor alpha. The net effect of these chemicals on the body is to help regulate BP, blood sugar, blood lipids, blood vessels’ health, healthy body weight, and a competent immune system.
The appetite center is under the influence of several hormones and chemicals. Cortisol depresses appetite. Glucagon secreted from the pancreas has a similar effect. Growth hormones and Gonadal hormones also regulate appetite. A gut peptide, Ghrelin, is produced by the stomach, which speeds up stomach emptying. Peptide YY and cholecystokinin are produced and have a similar effect to ghrelin.
High blood sugar and Ketones depress the appetite.
It may sound strange, but it is true that as the person gains weight, the mean energy expenditure (EEx) increases. As EEx increases, the person feels hungry because of stimulation of the appetite center. The reverse is also true: with weight loss, the EEx falls and the appetite center is depressed.
Non-Exercise-Activity-Thermogenesis (NEAT) regulates energy expenditure of activities of daily living. The basal metabolic rate (BMR) accounts for 70% of EEx, only 5 to 10% of EEx is required for voluntary activities, including work, exercise, etc. A person can burn at most 400 kcal/ hour by intense exercise, and marathon runners can burn 1200 kcal/hr.
To lose 1lb of flesh, one has to burn 2,500 kcal. It is not difficult to understand why losing the extra fat by exercising is difficult.
Hypothalamus produces and releases many peptides known collectively as hypothalamic peptides; by the actions of these, it maintains a balance between appetite, fat storage, and energy expenditure. Important peptides in this group are neuropeptide Y, Agouti-related peptide, alpha melanocyte-stimulating hormone, and melanocyte-concentrating hormone. An interaction between hypothalamic peptides and neural pathways via Serotonin, Catecholamine, and endocannabinoid receptors in various target tissues is ultimately responsible for maintaining steady body weight.
Appetite supressing drugs are coming to the market in increasing numbers, but none are safe for long-term use. These drugs act directly on the appetite center by increasing the production and release of a chemical group called monoamine. The pharmacological actions of norepinephrine, serotonin, and dopamine are enhanced by monoamine. These drugs may increase the risk of heart disease and high BP, as well as insomnia and nervousness.
The newer anti diabetic II oral drug, SGTP-2, and a weekly injection of Glucagon-Like Peptide-1 Inhibitors ( GLP-1) work in different sectors of metabolism and have a different safety profile.
Body mass index (BMI), height-weight nomograms, the thickness of skin fold of arms, and waist-hip ratio are helpful to identify obese individuals, but not all agree on a particular standard. An underwater determination of weight-volume ratio is an accurate measurement of obesity, but it is not a practical method.
A normal BMI is 20 to 25 kg/m2. A person is considered overweight if the number is between 26 and 29, and over 30 is considered obese. An increase in the waist-hip ratio of over 0.9 in women and 1.0 in men is taken as obesity.
The cause of obesity is unknown. Several factors have been implicated: heredity, environment, cultural habits, a viral infection of the GI tract, and sleep deprivation.
Several endocrine disorders like Cushing's syndrome, Hypothyroidism, Insulinoma, Hypogonadism and mental retardation also produce obesity.
Obesity increases the risk of heart disease, diabetes, high cholesterol, high BP, arthritis, and disturbances in sex-hormone-related diseases.
The body’s own regulating system of appetite, energy storage, and energy expenditure must be derailed before weight gain starts. If the process is allowed to progress unchecked for years, the person will be overweight or even obese.
edited May 2025
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