Weight loss is a hotly debated topic with a plethora of opinions, diets, and strategies on how to effectively shed pounds. But to truly understand how to lose weight, it’s important to dive into the science behind it. In short, weight loss is all about energy balance – the amount of calories you consume versus the amount of calories you burn. When you consume fewer calories than you burn, you lose weight.

But the physiology behind weight loss is much more complex than just calories in versus calories out. There are numerous factors that affect your body’s ability to lose weight, such as genetics, hormones, metabolism, and even the bacteria in your gut. Let’s take a closer look at the science behind each of these factors to better understand how weight loss works.


Your genes play a large role in determining your body weight and shape. Studies have shown that genetics can account for up to 80% of your body weight. This means that some people are genetically predisposed to be overweight and have a harder time losing weight. However, this doesn’t mean that weight loss is impossible for those with a genetic predisposition to obesity. It just means that achieving a healthy weight may require a bit more effort and potentially different strategies.


Hormones are chemical messengers that regulate various bodily functions, including hunger, metabolism, and fat storage. Two hormones that play a significant role in weight loss are ghrelin and leptin. Ghrelin is a hormone that stimulates hunger and increases food intake, while leptin is a hormone that signals fullness and promotes weight loss. Studies have shown that individuals who are overweight or obese tend to have higher levels of ghrelin and lower levels of leptin, making it harder for them to maintain a healthy weight.


Metabolism refers to the chemical processes that occur in your body to maintain life, such as breathing, digestion, and circulation. Your metabolism also plays a role in weight loss. When you eat, your body breaks down the food and converts it into energy. Your basal metabolic rate (BMR) is the number of calories your body burns just to keep you alive. The more muscle mass you have, the higher your BMR, meaning you burn more calories at rest. Individuals with a higher muscle-to-fat ratio have an easier time losing weight and maintaining a healthy weight.

Gut Bacteria

The estimated 100 trillion bacteria that live in your gut, also known as your gut microbiome, play a significant role in your health and weight. Research has shown that individuals who are overweight or obese tend to have different gut bacteria than those who are lean. Therefore, altering the composition of your gut microbiome may help with weight loss. This can be done by consuming probiotics and prebiotics, which are found in fermented foods and certain types of fiber.

In conclusion, weight loss is more than just calories in versus calories out. Genetics, hormones, metabolism, and gut bacteria all play a role in your ability to shed pounds. However, by understanding the science behind weight loss and implementing targeted strategies, such as building muscle mass and consuming probiotics, you can achieve a healthy weight and improve your overall health.