1. Due to obesity, the average life expectancy of people decreases by 7-8 years. Obesity shortens the average life expectancy by 10 years.
2. In the 21st century, the number of children and elderly people in the rich countries of the modern world has increased alarmingly. In America, 17% of people aged 2-19 and 36.5% of people aged 40-59 are obese.
3. Obesity causes more than 60 chronic diseases in humans. Diseases like heart disease, diabetes type-2, cancer, gout, high blood pressure, stroke, insomnia, liver, cardiovascular, gallbladder problems etc. are caused by obesity.
4. 64% of men and 77% of women with diabetes are obese.
5. Obese people work fewer days. Their work speed is slow.
6. Obesity is responsible for morbidity, disability and early death.
7. Obesity has been identified as one of the leading causes of death worldwide. Between 1.5-3.6 million people in the United States and 1 million in Europe die each year from obesity.

1. Unhealthy eating habits
(i) People become obese if they consume excess fat and calorie rich food.
(ii) Consuming more than normal amount of food leads to obesity.
(iii) Excessive consumption of fast food is responsible for obesity.
(iv) Excessive fluid intake leads to obesity.
(v) Obesity is caused by eating sweet foods (carbohydrates), sugary desserts, drinking alcohol, fast food etc.
2. Life style
(i) Living in luxury and spending idle time.
(ii) Consuming excess outside food.
(iii) Minimizing physical exertion. Not exercising regularly.
(iv) Long hours of watching TV, working on computer and browsing internet.
(v) To engage in non-manual employment. Going by car instead of walking.
3. Genetic factors: obesity tends to run in the same family members. This is also observed in twin siblings. The number of fat cells in the body is high due to obesity. Because genes control the similarity between them. Gene Polymorphism Regulates Human Appetite and Metabolism Increases Obesity. People who carry the FMO (Fat Mass and Obesity Associated) gene are overweight. Again, genetic defects also cause obesity. Mutations in melanoctin and leptin genes cause obesity.
4. Social preferences: In many societies around the world, fatness is considered a matter of nobility and pride. They consider obesity a symbol of good health and happiness. So they want to gain weight by consuming more food. However, modern society does not support this misconception.
5. Effect of smoking: The effect of smoking on obesity is negligible. But those who quit smoking gained an average of 4.40 kg (9.7 lb) for men and 5 kg (11 lb) for women over a 10-year period.
6. Pregnancy: Most women gain 5-6 pounds with each pregnancy. Conceiving at an older age is more likely to gain weight. Many women do not lose that weight after childbirth. As a result obesity increases.
7. Emotions: Depression, hopelessness, anger, boredom, irritability, inferiority complex etc. lead to obesity.
8. Temperature: If the temperature variation of the environment decreases, people can become fat.
9. Gender: Men have more muscles than women. Muscle tissue uses more calories. Therefore, women accumulate more fat and gain weight than men even if they eat the same amount. 64% of men and 77% of women suffer from diabetes due to obesity.
10. Diseases: Polycystic Ovary Syndrome, Cushing’s Syndrome, Hypothyroidism, Prader Willi Syndrome etc.
11. Insomnia: Sleeping less than seven hours a night causes hormonal changes. Hunger increases. Body weight increases due to excess food intake.
12. Medications: Certain medications can cause weight gain or changes in body composition. These include insulin, steroids, sulfonylureas, thiazolidinediones, birth control pills.
13. Lack of education: Many are unaware of the harmful effects of obesity. This is happening due to lack of knowledge about balanced diet and good health, lack of understanding about the causes and problems of obesity, overfeeding of children etc.

The formula for measuring human obesity is Body Mass Index-BMI. A person with a BMI of 30 kg/m2 is considered obese. There are three types of obesity.
1. Severe obesity: BMI ≥ 35 or 40 is called severe obesity.
2. Morbid obesity: BMI ≥ 40 or 44.9 is called morbid obesity.
3. Obesity: BMI ≥ 45 or 50 is called super or overweight.

Abnormal accumulation of excess fat in the body is called obesity. A person with 20% or more body fat is considered obese. Consuming more food energy than the body needs leads to obesity. For every 9.30 calories of food consumed, 1.0 grams of fat is stored. The branch of medicine that deals with the causes, symptoms, treatment and prevention of obesity is called Bariatrics.

Body Mass Index is abbreviated as BMI. The value obtained by dividing a person’s weight (kg) by the square of his height (metres) is called BMI. The formula for measuring BMI is:

The process by which absorbed simple food participates in the formation of the body or protoplasm in the organism is called assimilation.
1. Carbohydrate assimilation: Carbohydrates are digested into glucose, fructose and galactose. Glucose, fructose and galactose are absorbed by body cells. Absorbed glucose is burned in the body’s cells to produce energy. Excess glucose is stored as glycogen. Small amounts of monosaccharides are converted to proteins and lipids.
2. Protein assimilation: Protein is digested and converted into amino acids. Amino acids are absorbed by body cells. Absorbed amino acids form protoplasm, cytoplasm, enzymes, hormones etc. Some amino acids are oxidized to produce energy. Small amounts of amino acids are converted to sugars.
3. Lipid assimilation: Lipids are digested and converted into fatty acids and glycerol. Fatty acids and glycerol are absorbed by body cells. Absorbed fatty acids and glycerol form phospholipids, lipoproteins, cholesterol etc. in body cells. Some are stored as fat under the skin as food. A small amount is synthesized as carbohydrates and proteins.

The process in which the semi-solid or soft digested waste of food is expelled from the digestive tract as faeces is called defecation or egestion. Stool-like material is moved from the colon to the rectum by the contraction waves of the colon muscles or the process of peristalsis. A slippery mucous substance secreted from the colon wall acts as a lubricant to facilitate stool passage. When the bladder is full to a certain degree, pressure is created on its walls. It causes defecation reflex and urges to pass stool. Stool enters the anus under the pressure of the rectal wall and pelvic muscles. Stool is expelled through the anus by the peristalsis action of the anus. Two sphincter muscles located in the anus control the passage of stool. Pain, fear, temperature, physical or neurological complications affect the process of defecation.

The thick, cylindrical and grooved part of the small intestine extending from the ileum to the anus is called the large intestine. The function of the human colon is described.
1. Absorption and Reabsorption: Water, mineral salts, sodium, chloride etc. are absorbed by the colon. 70-80% of the water present in the digestive waste is reabsorbed by the colon.
2. Reservoir of microorganisms: The appendix of the colon is said to be a protected reservoir of beneficial microorganisms. 500 species of bacteria live in the human colon. Bacteria in the appendix reestablish the intestinal bacterial flora when beneficial gut bacteria are destroyed. These bacteria break down non-nutritive food ingredients to produce short-chain fatty acids.
3. Fermentation and Digestion: There are 500 species of mitotic bacteria in the large intestine. These bacteria break down raw food ingredients in a fermentation process to produce short-chain fatty acids and release carbon dioxide, hydrogen and methane gases. Small fatty acids (acetic acid, propionic acid and butyric acid) provide energy to the cells of the colon wall.
4. Faecal production: Liquid chyme or mucus from the small intestine enters the large intestine and is absorbed into moist and soft stools. Usually 135 grams of feces are produced from 350 grams of feces.

The process by which digested food enters the blood and lymph from the alimentary canal is called absorption or absorption of food. The small intestine is the main site of absorption. Small intestine absorbs about 90% of food. 10% is absorbed by the stomach and colon. The lining of the small intestine folds to form a finger-like projection. It is called Vilai. Vilai increases the absorption capacity of the intestine by 40 times. There are about 500,000 villi in the human small intestine. The fine projections in villi cells are called microvilli. Microvilli join together to form a brush border. Controls the brush border absorption process. Microvilli increase the absorption capacity of the intestine by 60 times. Food is absorbed by endocytosis along with vitamins, minerals and water.
1. Protein Absorption: Proteins are digested to produce amino acids. Protein is absorbed in the small intestine as amino acids. However, semi-complex proteins like peptones, proteoses, peptides etc. are also absorbed in very small amounts. Egg whites, shrimp, crab etc. are absorbed unchanged. Amino acids are absorbed by the villi of the duodenum and jejunum through the process of active absorption, diffusion and phagocytosis. Normally, L-amino acids are absorbed by the active pathway and D-amino acids by absorption. The cytoplasmic tubule of Vilai functions in the absorption of proteins. Thyroxine hormone regulates protein absorption.
2. Absorption of sugars: Sugars are digested into monosaccharides like glucose, fructose, galactose, lactose, sucrose, xylose, mannose etc. The small intestine absorbs sugars as monosaccharides. However, some sugars are also absorbed as disaccharides. Of the monosaccharides, 80% are absorbed as glucose and 20% as fructose and galactose. With the help of Na+ and ATP, the tubules of the villi of the jejunum absorb glucose. Fructose is absorbed in the digestive process. Sucrose and lactose are absorbed in the duodenum and small intestine.
3. Lipid Absorption: Lipids are digested into fatty acids, glycerol, monoglycerides and cholesterol. Fatty acid absorption is a complex process. Fatty acids, monoglycerides and bile salts bind together to form micelles. Micelle particles are absorbed by the duodenum and mid-small intestine. Under the influence of thiokinase enzyme, fatty acids are converted into active fatty acids. Active fatty acids, glycerol and proteins join together to form triglycerides. These are called chylomicron particles. Chylomicron particles enter the lymphatic vessels of the small intestine. If the branches of the lymphatic duct are white, it is called lactial. Chylomicrons enter the blood plasma through lymphatic vessels. Enzymes located in the plasma break down chylomicrons or lipoproteins to form fatty acids and glycerol.
4. Water Absorption: Water is absorbed by the epithelial cells of the villi of the small intestine. Normally 200-400 ml of water is absorbed per hour.
5. Mineral Salt Absorption: Mineral salts are absorbed by the epithelial cells of the villi of the colon.
6. Absorption of Vitamins: Vitamins are absorbed when dissolved in water or fat by the epithelial cells of the villi of the small intestine.
Absorption of nutrients is a very important process for the body. Digestion produces amino acids from proteins, glucose and fructose from sugars and fatty acids and glycerol from lipids. The small intestine absorbs all the digested food. Then it reaches different parts of the body through the blood. Body cells take all these nutrients and stay healthy, strong and fresh.

If the food digestion process is controlled by the nervous system, it is called nervous control. The neural network in the wall of the human colon plays a major role in food intake and digestion. There is a hunger center in the hypothalamus of this brain. It regulates human appetite and food intake. Two nerves control digestion in humans.
1. Intrinsic plexuses: The nervous system that controls digestion by receiving stimuli from inside the alimentary canal is called intrinsic plexus. It is called enteric or enteric nervous system. The enteric nervous system is called the second brain of humans. It extends like a web in the walls of esophagus, stomach, small intestine and colon and receives stimulation from there. Two types of intrinsic neural networks control short reflexes.
(i) Myenteric plexus: It controls the contraction or peristalsis action of the smooth muscles of the digestive tract.
(ii) Submucosal plexus: It controls the secretion of chemicals in the digestive system.
2. Extrinsic plexuses: The nervous system that controls digestion by receiving stimuli from outside the alimentary canal is called extrinsic plexus. It consists of sympathetic and parasympathetic. It regulates the long reflex action of the digestive system. They release acetylcholine and adrenaline. Acetylcholine powers the flow of food and drink through the alimentary canal. Besides, it helps to secrete more digestive juices from the stomach and pancreas. Adrenaline relaxes stomach and intestinal muscles and reduces blood flow.