Researchers fed mice different types of fat to see how their bodies responded. They discovered that mice eating lard (a type of animal fat) at higher levels developed more brown fat—a special type of fat that burns calories to create heat—compared to mice eating soybean oil. The lard-eating mice also had changes in their gut bacteria that appeared beneficial. While this is interesting mouse research, scientists need to study humans to know if the same effects would happen in people.

The Quick Take

  • What they studied: Whether eating lard versus soybean oil affects how much brown fat your body makes and changes your gut bacteria
  • Who participated: 60 young male mice that were fed controlled diets for 20 weeks with different amounts of lard or soybean oil
  • Key finding: Mice eating lard at the higher fat level (25% of calories) developed significantly more brown fat and had better fat-burning genes activated compared to mice eating soybean oil
  • What it means for you: This suggests animal fats like lard might help your body burn more calories through brown fat, but this is early mouse research—human studies are needed before changing your diet based on these findings

The Research Details

Scientists divided 60 young male mice into four groups. Two groups ate diets where lard provided either 15% or 25% of their daily calories, while the other two groups ate the same amounts of soybean oil instead. The mice ate these controlled diets for 20 weeks. At the end, researchers examined the mice’s tissues, measured specific genes related to fat burning, and analyzed the bacteria living in their digestive systems using genetic testing.

The researchers specifically looked for brown fat, which is different from regular white fat. Brown fat is special because it burns calories to create warmth in your body. They measured how much brown fat developed, checked which genes were turned on or off, and counted the different types of bacteria in the mice’s guts.

This type of study is called a controlled experiment because the scientists carefully controlled exactly what the mice ate and compared the results between groups. This helps them see if the type of fat (lard vs. soybean oil) made a real difference.

This research matters because understanding how different types of fat affect brown fat development could eventually help people manage their weight and metabolism. Brown fat is considered ‘good fat’ because it burns calories rather than storing them. If scientists can figure out which foods help activate brown fat in humans, it might offer a new way to help with weight management. The gut bacteria findings are also important because we’re learning that the bacteria in our digestive system affect our overall health.

This study was well-designed with a clear comparison between two groups and careful measurement of results. The researchers used established scientific methods to measure genes and bacteria. However, this is mouse research, which means the results may not directly apply to humans. Mice have different bodies and metabolisms than people. The study only looked at young male mice, so we don’t know if the results would be the same in females or older mice. The study was published in a peer-reviewed journal, meaning other scientists reviewed it before publication.

What the Results Show

The most important finding was that only when fat made up 25% of calories did lard show clear advantages over soybean oil. At this higher fat level, mice eating lard had significantly more brown fat tissue compared to the soybean oil group. The mice eating lard also showed higher levels of a special protein called UCP1, which is the key protein that makes brown fat burn calories to create heat.

When researchers looked at the genes in the fat tissue, they found that mice eating lard had much higher activity in genes related to fat burning and heat production. At the same time, genes related to storing fat were less active in the lard group. This suggests that lard may have encouraged the body to burn fat rather than store it.

The gut bacteria also changed in interesting ways. Mice eating lard had higher amounts of four types of bacteria: Akkermansia, Romboutsia, Lactobacillus, and Streptococcus. These bacteria are generally considered beneficial for health. The diversity and balance of bacteria in the gut is thought to be important for overall wellness.

Interestingly, at the lower fat level (15% of calories), there were no significant differences between the lard and soybean oil groups. This suggests that the amount of fat in the diet matters—the effect only showed up at the higher fat level. This finding is important because it tells us that not all fat amounts produce the same results. The researchers also noted that the changes in brown fat and gene expression were linked to the changes in gut bacteria, suggesting these systems may work together.

Previous research has shown that brown fat can be activated by cold exposure and exercise, but less is known about how diet affects brown fat development. Some earlier studies suggested that different types of fat might affect metabolism differently, but results have been mixed. This study adds to growing evidence that the type of fat we eat (animal fat versus plant oil) may matter for how our bodies handle energy and metabolism. The findings about gut bacteria align with recent research showing that diet shapes which bacteria live in our digestive system, and these bacteria influence metabolism.

This study has several important limitations. First, it was done in mice, not humans, so we cannot assume the same effects would happen in people. Mice have different digestive systems, metabolism, and genetics than humans. Second, the study only included young male mice, so we don’t know if the results would apply to females or older animals. Third, the study was relatively short (20 weeks), so we don’t know if these effects would continue long-term or if the body would adapt over time. Finally, the study used purified laboratory diets that don’t reflect real-world eating patterns, so the results might not apply to normal food consumption.

The Bottom Line

Based on this mouse research, we cannot yet recommend that people change their fat intake. While the findings are interesting, human studies are needed before making dietary changes. If you’re interested in activating brown fat, current evidence supports exercise and cold exposure as proven methods. Always consult with a healthcare provider before making significant dietary changes, especially if you have health conditions or take medications.

This research is most relevant to scientists studying metabolism, obesity, and nutrition. People interested in weight management and metabolism may find it interesting as background information. However, this is not yet ready to guide personal dietary decisions. People with specific health conditions should definitely talk to their doctor before changing their fat intake based on any research.

Since this is mouse research, we cannot predict how quickly effects would appear in humans, or if they would appear at all. Even if human studies confirm these findings, changes in brown fat and metabolism typically take weeks to months to become noticeable. Any real-world application would require much more research.

Want to Apply This Research?

  • Track daily fat intake by type (animal fats vs. plant oils) and monitor energy levels and body composition monthly to see if patterns emerge over time
  • If interested in brown fat activation, use the app to log regular exercise sessions and track cold exposure activities (like cool showers), which are proven brown fat activators
  • Create a long-term tracking system that records fat type consumed, exercise frequency, and monthly body measurements or energy assessments to identify personal patterns

This research was conducted in mice and does not directly apply to humans. Before making any changes to your diet, especially regarding fat intake, consult with a healthcare provider or registered dietitian. This information is for educational purposes only and should not replace professional medical advice. People with heart disease, high cholesterol, diabetes, or other health conditions should be particularly cautious about dietary changes and must discuss them with their doctor first.