Microbiome and excess weight: why counting calories doesn't work and what does the science really say?

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We all know people who can eat cake all night and not gain weight, while others can gain weight just by looking at dessert. For decades, we’ve been told that the secret to weight loss is simple math: eat fewer calories than you burn. But modern science is proving that this formula is a dead end. The real mastermind behind our weight, our metabolism, and our eating habits lies deep inside. It’s our gut microbiome.

The metabolic machine in your stomach

To understand how bacteria affect weight, imagine that there is a large invisible animal living in your stomach that needs to be fed. When we eat, we are not only feeding our own cells, but also trillions of microorganisms.

Scientists explain this mechanism very simply: if your microflora is depleted and poor (for example, due to frequent diets or taking antibiotics), it "steals" less food from you. As a result, you absorb almost all the calories from your dinner and rapidly gain weight. In contrast, people with a rich, diverse and energy-intensive microflora spend the lion's share of what they eat on feeding it. Their bacteria literally burn excess calories for them.

Experiments on mice showed striking results: rodents that had most of their intestinal bacteria removed began to gain weight rapidly, as microbes stopped taking part of their food.

The paradox of one apple

Why classic diets don't work? Because they focus on product labels, not people.

If you give a regular apple to different people, their bodies will react completely differently. Each person will digest this apple in their own way, take different nutrients from it and, most importantly, get a different amount of energy. It depends on which strains of bacteria dominate in the intestines. For example, the presence of a large number of the bacterium Bifidobacterium adolescentis can be a marker of excess weight, because it has the ability to convert certain substances (glucocorticoids) in a way that leads to metabolic pathologies.

Alteration of the gut microbiome leads to metabolic diseases and obesity through several mechanisms: increased permeability of the intestinal walls (toxins enter the bloodstream), insulin resistance occurs, the balance of short-chain fatty acids (SCFAs) is disrupted, and systemic inflammation occurs.

Genetics or Lifestyle? Twin Studies

Many people blame their excess weight on “bad genes” or a “slow metabolism.” However, science has a different opinion.

A study of identical twins (with exactly the same genetics) who were placed in different families, lived in different countries, and led different lifestyles after birth showed that their microbiomes differed dramatically as adults, with one twin being severely obese and the other not.

This proves that differences in the microbiome are formed throughout life, influenced by our environment, stress levels, and diet. As scientists aptly put it: “You get the microbiome you deserve.”

4 scientific steps to a healthy weight

If you want to lose weight and keep it off, you need to stop fighting your body and start negotiating with your microbes.

1. Stop taking probiotics blindly

Buying a drug with 36 strains of bacteria at the pharmacy without testing is dangerous. You can destroy the beneficial bacteria that you still have. Obesity is a complex disease, so treatment should begin with a personalized genetic study of the intestinal microbiome (its metabolomic analysis) to determine exactly which microbes are causing weight gain in you.

2. Feed the “right” animals

Scientists emphasize: we need to eat more than 50 grams of dietary fiber (fiber) per day. Legumes, beans, various vegetables and fruits contribute to the growth of beneficial bifidobacteria. The more different plants in your diet, the richer your microbiome and the easier it is for you to control your weight.

3. Fermented foods instead of artificial sweeteners

Add yogurt, sauerkraut, and kefir to your diet—they contain natural lactobacilli that reduce the number of pathogens. Instead, avoid artificial sweeteners (like aspartame). They raise blood sugar levels and stimulate the growth of enterobacteria that contribute to obesity.

4. Personalized nutrition

Your food preferences are often dictated by your bacteria. To change your weight, you need a personalized nutrition plan based on your microbiome analysis. Such a plan uses food as medicine, suppressing pathogens and multiplying beneficial flora, allowing you to restore a healthy metabolism.

Being overweight isn't a lack of willpower. It's a signal from your super organ that the ecosystem inside you needs help. Restore the balance of your microbiome, and your body will thank you with health and slimness.