New research from the University of Copenhagen suggests that the microbes in our guts may extract the energy from our food differently in each individual, which may explain why some people may gain more weight than others do, despite eating similar diets.

You might eat a cookie and it goes straight to your hips, while your BFF looks like she's never put an iota of sugar in her body, even though she ate the same cookie with you. Researchers from the University of Copenhagen's Department of Nutrition, Exercise and Sports looked at the gut microbes of 85 Danes to see how effective and efficient they were in extracting energy from food that's eaten. They found that a portion of the sample population had gut microbes that extracted more energy than the others, which could be a step in the quest to understand why some people gain more weight than others, despite similar dieting habits.

To do this, they looked at the 'residual energy' in the poop of 85 Danes while also mapping the composition of gut microbes for each of the 85. They found that about 40% of the participants were in a group that on average, extracted more energy from food than the other 60% did.

They also noted that those who extracted the most energy from the food weighed about 10% more on average than average. Energy and calories are closely tied, as calories are the amount of energy released when your food is broken down and absorbed (digested).

Professor Henrik Roager is with the University of Copenhagen and said that they may have a key to understanding why some people simply gain more weight than others, though further investigation needs to happen. The results also suggest that being overweight may not be directly tied to how healthfully you eat or even the amount of exercise you get as it could also be the composition of your gut microbes.

The participants were divided into three groups that were determined by the composition of their gut microbes. One group was the 'B-type' composition and was dominated by Bacteroides bacteria. This group was found to be more effective at extracting nutrients from food and found in 40% of the participants.

The researchers believe that a portion of the population may have gut bacteria that are too effective at extracting energy, and this may give them more calories from the same amount of food another with less effective extraction would have.

Professor Roager also said that it's a good thing that our gut bacteria extract energy from food. The bacteria's metabolism of food gives extra energy in beneficial forms like short-chain fatty acids, and our bodies can use those as energy-supplying fuel.

But as with any other calorie, if we have more than we can burn, it could increase obesity risk over time.

The researchers also looked at the travel time in the participants' guts and found that from mouth to the rectum (moving through the esophagus, stomach, duodenum, and small and large intestines) it takes about 12-36 hours. This is when the body is extracting all the nutrients from the food.

They hypothesized that those who had long digestive times would get the most nutrition from their food because the body had longer to extract it. Surprisingly, they found just the opposite! The participants with the B-type gut bacteria (and who extracted the most energy) also had food pass through their gastrointestinal system the most quickly.

The team was quick to note that while it was interesting that the group of people who had less energy in their poop (so more extracted in the digestive process) were also the ones who weighed more on average--there isn't a direct relationship and they want to explore more in the future.

Still, it stands to reason that if your body is super efficient at extracting energy and nutrients that you don't end up burning off, they could add weight eventually.

Humans are typically divided into three bacteria groups based on presence and abundance: B-type (Bacteroides), R-type (Ruminococcaceae) and P-type (Prevotella). Interestingly, the B-type is more often found to be predominant in individuals with a high intake of protein and animal fat (thought more like a Western diet), whereas the P-type is more predominant in individuals that consume diets rich in carbohydrates and fiber.

So not a bad idea to consider your carb and fiber intake and keep those P-type microbes happy!