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Obesity and Microbiota

Trillions of bacterial communities live in multiple parts of the human body. The number of these bacteria is 10 times more than all the cells in our body. Although they are very very small, their total weight is around 2-3kg. Anatomically, they are found in increasing numbers from the small intestine to the large intestine and the least numbers are in the esophagus and stomach. They are most concentrated in the large intestine. This community of bacteria living with us in our body is called the microbiota. The genetic content of these bacteria is also called the microbiome. 

Intestinal microbiota has effects on nutrition, immunity, behavior and some chronic diseases. The microbiota functions as a metabolic, endocrine and immunological organ. Intestinal microbiota performs some functions that the human body cannot fulfill, causing a symbiotic relationship. It ensures the digestion of some indigestible foods, synthesizes some vitamins and micronutrients, neutralizes dietary toxins and carcinogenic substances, contributes to the excreting of cholesterol and bile acids, contributes to the health of intestinal cells, regulates intestinal blood supply and prevents the proliferation of harmful bacteria in the intestines. 

Our gut is where bacteria are most concentrated. The intestinal microbiota begins to develop while in the womb. During birth (normal birth) and breastfeeding, the baby continues to acquire bacteria. Over time, a unique microbiota develops for almost every individual. The content of this microbiota is shaped by the mode of delivery (normal birth/cesarean section), antibiotic treatment, nutrition (breast milk or formula), and environmental factors. At the age of 3, the intestinal microbiota is largely formed. It remains largely constant throughout adulthood. With age and changes in our diet, changes occur in the physiology of the digestive system. Intestinal microbiota is easily affected by nutrition, drugs and dietary factors. Even a single dose of antibiotics can cause changes in the microbiota. 

There are many causes of overweight and the process is not fully understood. In humans, the difference in microbiota between obese and thin individuals suggested that microbiota may have an effect on obesity. Today, it is known that the intestinal microbiota is associated with obesity.

 The relationship between the intestinal microbiota and obesity was first revealed by studies conducted with experimental animals that were microbe-free, that is, bacteria-free and raised in special environments. It was observed that germ-free rodents needed 30% more nutrients to maintain their body weight compared to normal individuals. Although germ-free mice consume more food; Normal mice had 40-45% more fat than germ-free mice. Transplanting intestinal microbiota from normal mice to germ-free mice showed an increase in fat of approximately 60% within two weeks in germ-free mice. This increase was accompanied by insulin resistance, fat cell hypertrophy, and an increase in leptin and glucose levels in the blood. When the germ-free mice were fed a diet rich in sugar and fat, they were not obese. The findings showed that the intestinal microbiota was associated with obesity. This is explained by the fact that the intestinal microbiota increases energy efficiency by contributing to the digestion of indigestible foods.

It is known that low-dose antibiotic treatment has an effect on weight gain in mammalian farm animals (sheep, cows, pigs). Especially in the early postpartum period, weight gain is observed in animals given low-dose antibiotics. Antibiotics have been used to promote weight gain in farm animals for many years. Antibiotics show this effect by changing the intestinal microbiota. This raises the question of whether it can have a similar effect in humans. The first published epidemiological studies showed that exposure to antibiotics during infancy was associated with an increased body mass index.

Many studies have shown that there are microbiota differences between obese and thin individuals. The microbiota observed in obese individuals may contribute to the development of obesity by causing changes in the hormonal processes related to fullness. The microbiota may also contribute to obesity by contributing to the development of intestinal cells, digestion and absorption of nutrients. Changes in the intestinal microbiota have been observed with weight loss after various bariatric surgeries and diet. All these findings indicate a relationship between microbiota and obesity.

Although the effects of intestinal microbiota on obesity are not fully known; more detailed studies can reveal cause-effect relationships more clearly. Changing the intestinal microbiota may help treat obesity in the future.

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