It’s not uncommon for partners or groups of dieters to eat the same food, follow the same routines, and still see very different results—especially when it comes to weight loss. Often, this gets chalked up to vague explanations like “you have a faster metabolism,” “my body just holds on to weight,” or “everyone’s different.”
A new study suggests that part of that difference may come from much deeper inside the body—specifically, from the microbes living in your gut.
Researchers found that some people’s gut microbiomes are better at extracting extra calories from high-fiber foods than others.
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An Oddball in Your Gut
Your microbiome—the bustling ecosystem of trillions of microbes living in your gut—is highly personal, much like a fingerprint. It’s shaped by your genes, long-term diet, lifestyle, medications, and even your environment. One lesser-known way microbiomes differ is in how much methane they produce.
A study published in The ISME Journal found that people whose microbiomes produce more methane tend to extract more energy from high-fiber foods than those whose guts produce little or none. In other words, the same meal may deliver different calorie amounts depending on who’s digesting it.
“It shows people on the same diet can respond differently,” said Blake Dirks, a graduate researcher at Arizona State University’s Biodesign Center for Health Through Microbiomes and lead author of the study. “Part of that is due to the composition of their gut microbiome.”
How Fiber Turns Into Energy—And Where Methane Comes In
Humans can’t digest most dietary fiber on their own. Instead, fiber passes through the stomach and small intestine largely intact into the colon, where gut microbes take over.
There, beneficial bacteria, such as Bifidobacterium, ferment fiber into short-chain fatty acids (SCFAs), like acetate, propionate, and butyrate. These compounds are absorbed by the body and used as energy. During fermentation, microbes also release gases such as carbon dioxide and hydrogen.
Hydrogen, however, can’t accumulate indefinitely. When too much builds up, it makes the gut environment less favorable for fermentation, slowing or even stalling the process—essentially acting like a built-in braking system.
In a healthy gut ecosystem, other microbes help clear this excess hydrogen. Methanogens, for example, consume hydrogen and convert it into methane. Other microbes convert hydrogen into hydrogen sulfide. By removing hydrogen, these microbes relieve the fermentation “brake,” allowing fiber breakdown to continue efficiently.
Because the human body doesn’t produce methane on its own, the researchers suggest methane may serve as a useful biomarker—a signal of a microbial ecosystem that’s especially efficient at fermenting fiber and extracting energy from it.
Some Are Methane Producers, Some Are Not
Researchers from Arizona State University analyzed data from a previously conducted, tightly controlled feeding study involving 17 healthy adults. Each participant served as their own control and followed two diets:
A Western diet, low in fiber, highly processed, and easily absorbed in the small intestine.
A microbiome-enhancer diet, rich in fiber, resistant starch, and whole foods, designed to deliver more fuel to gut microbes in the colon.
During each diet phase, participants lived for six days in a whole-room calorimeter, a specialized chamber that allowed researchers to precisely measure energy intake, energy expenditure, energy lost in feces, and continuous methane production from both breath and gas.
Researchers also collected blood and stool samples and performed detailed microbiome sequencing.
The results showed a clear divide: some participants produced large amounts of methane, while others produced almost none. Those who produced more methane tended to have methanogen-rich microbiomes, higher blood levels of certain SCFAs, and—on the high-fiber diet—significantly higher metabolizable energy, meaning they absorbed more calories overall.
Why This Matters
Many people choose high-fiber, whole-food eating patterns—such as the Mediterranean diet—because they’re linked to better heart health, gut health, and metabolic outcomes, and because fiber-rich foods are generally lower in calories than ultra-processed options. This study doesn’t challenge those benefits. In fact, participants still absorbed more total calories from the Western diet regardless of methane production.
What the findings do highlight is the emerging role of precision nutrition—the idea that optimal diets may differ based on individual biology, including the gut microbiome. Precision nutrition doesn’t stop at microbes; it also considers factors like age, sex, physical activity, metabolic health, medical conditions, and genetics.
For some people, high-fiber foods may feel especially filling and calorie-light. For others with methane-producing microbiomes, those same foods may quietly deliver more energy than expected—not because fiber is “bad,” but because their microbes are particularly efficient at extracting it.
Your Biology Matters More
High-fiber diets aren’t the problem—they remain one of the healthiest ways to eat. But this study shows that even subtle differences in gut microbes can influence how much energy we actually absorb from the same foods.
As nutrition science moves toward personalization, understanding how individual microbiomes interact with diet may help explain why “one-size-fits-all” advice doesn’t always fit—and why listening to both your plate and your biology may matter more than we once thought.
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