Why Do Some People Gain Weight Faster Than Others? Science Lands On A Theory

We all have that one friend who seems to be able to eat whatever they want without gaining weight. And if you've ever wondered why you seem to gain or lose weight more effortlessly than the people around you, science1 suggests something called hyper-efficient bacteria may be to blame.

Is your gut an overachiever?

Scientists at the University of Copenhagen recently discovered that some microbes extract more energy from food than others. People who have these super-biomes then might have more food leftover to be stored as fat.

In other words, if you gain weight easily, your gut microbiome might just be really, really good at its job.

Researchers measured the leftover energy in study participants' excreted matter (ahem, their poop) to estimate how well their gut bacteria extracted energy from their meals, all while closely studying the types of microbes in each of their guts.

The scientists found that approximately 40% of the participants had gut microbial makeups that extracted energy more efficiently. That group of people also tended to weigh about 20 pounds more.

"We may have found a key to understanding why some people gain more weight than others, even when they don't eat more or any differently," Henrik Roager, Ph.D., a study author, said in a statement.

One size rarely fits all

This finding suggests that the old "calories in, calories out" strategy for weight management may just be a crock of, erm...excreted matter. Your gut microbiome makes a difference too.

The study results also contribute to a growing body of evidence pointing toward bio-individuality, or the concept that our bodies are all uniquely complex, and what creates change for one person may have the opposite effect for another—or have no effect at all. (Just consider one 2016 study in Nutrition & Metabolism that found that mice that received a gut bacteria transplant2 from leaner mice lost weight.)

However, it's too early to tell whether this study proves direct causation. "It is very interesting that the group of people who have less energy left in their stool also weigh more on average. However, this study doesn't provide proof that the two factors are directly related. We hope to explore this more in the future," says Roager.

Efficient or not, the health of your gut is important

If you feel like you might fit into this category of people who store more fat than others on average, it may be frustrating if you've tried to manage or lose weight.

There's a lot more to learn, but some beneficial bacteria may help directly counter the effects of hyper-efficient gut bacteria and other weight-gain-promoting factors.

The takeaway

A human study found that people whose microbiomes were, on average, more efficient at extracting energy from food, tended to weigh more by a significant margin. The researchers theorize that these hyper-efficient microbiomes can lead to an excess of stored fat and a greater risk of obesity.

This may explain why some people gain weight more quickly than others, and it definitely reiterates how essential our gut microbiome is for pretty much every aspect of our health.