Author: Judīte Lukša
Human weight is influenced by many different factors such as diet, exercise, genetics, environment, hormones. But did you know that your weight is also affected by the microorganisms in your body?
There is a saying that you’re never dining alone. And it’s true, because every time you eat anything, you’re feeding a hundred trillion microbes (to make it easier to imagine – one trillion is all the world’s population multiplied by about 1400). 
During a lifetime, the digestive system is colonized by different types of microorganisms, including bacteria, viruses, fungi, collectively known as the gut microbiota.  The gut microbiota begins to affect your body the moment you are born. You are first exposed to microbes when you pass through your mother’s birth canal. However, new evidence suggests that babies may come in contact with some microbes while inside the womb .
Although many different types of microbes live inside you, bacteria are the most studied.  It is known that most of the human population’s microbiota is composed of 5 types of bacteria – Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria, and Verrucomicrobia, withBacteroidetesand Firmicutes being around 90% of the total bacterial species. 
In fact, there are more bacterial cells in your body than human cells (roughly 40 trillion bacterial cells in your body and only 30 trillion human cells). That means you are more bacteria than human. 
Why do we need these microorganisms?
Altogether, these microbes weigh about 1–2 kg, which is roughly the weight of your brain. Together they function as an extra organ in your body and play a huge role in your health. 
These microbes serve a number of important functions, including:
- producing additional energy otherwise inaccessible to the host by breaking down carbohydrates that are not digested in the intestine;
- producing B group vitamins and vitamin K;
- metabolizing chemical substances (such as the inactivation of substances formed in meat during cooking) and drugs;
- protecting us from the overgrowth of pathogenic (bad) bacteria;
- assisting in the development of the immune system. [2, 5]
Overall, current evidence supports the potential role of the human gut microbiota in obesity. There are data that suggest that the bacterial composition of gut microbiota differs between obese and skinny individuals and that a Western-style diet which is high in fat and refined carbohydrates may promote increased intestinal bacteria linked to obesity. This raises the question whether altering the microbiota can modulate obesity risk and whether knowledge about an individual’s microbiota can be used to develop personalized diets for obesity prevention. 
Most studies of overweight and obese people show a dysbiosis (changes in the types and numbers of bacteria) characterized by a lower diversity.  “The greater the diversity, the skinnier the person. If you’re carrying too much weight, your microbes aren’t as diverse as they should be,” says Prof. Spector, who found the same pattern in a study of 5,000 people. 
Lower bacterial diversity than in healthy people has also been observed in people with inflammatory bowel disease, psoriatic arthritis, type 1 diabetes, atopic eczema, coeliac disease, type 2 diabetes, and arterial stiffness.  An interesting finding was that obesity-resistant bacteria-free mice become obese and increase their energy harvest and caloric uptake after receiving a microbiota transplant. 
The composition of the intestinal microbiota is strongly affected by dietary patterns.  Having a healthy and varied diet, rich in different sources of fiber, has been shown to create a more diverse range of gut microbes.
Good sources of dietary fiber include:
- wholegrain breakfast cereals;
In addition to the composition of the diet, gut microorganisms are also affected by the energy content of the diet, age, fasting, and the use of antibiotics.[2,5]
Of course, gut bacteria affect our weight but that doesn’t mean that only microorganisms are to blame. I will hurt you and say that healthy eating and physical activities are still extremely important to maintain our body weight at normal range. I hope you stay fit and remember that fiber-containing food is a key nutrient for a healthy microbiota and it means also a healthy you.