Gut response: Cooked food alters guts’ microbial ecosystems, study reveals

03 Oct 2019 --- Cooking food fundamentally changes the microbiomes of both mice and humans, according to an unprecedented study from the University of California San Francisco (UCSF) and Harvard University, US. While several microbiome studies have compared diets with divergent ingredients, the everyday practice of cooking has previously remained understudied. Published in Nature Microbiology, this study reveals the role that environments and eating behaviors can play in optimizing microbial health.

The researchers admitted they were surprised to discover that no one had studied how cooking itself alters the composition of the microbial ecosystems in human guts. They examined the influence of cooking on the microbiomes of mice by feeding diets of raw meat, cooked meat, raw sweet potatoes or cooked sweet potatoes to groups of animals. These were selected as prior data demonstrated that cooking alters the nutrients and other bioactive compounds in both meat and tubers. The findings also show that gut health is not only dependent on which food we eat, but also on the way we eat it. 

Indeed, the way we eat food also includes the foods that we pair up in meals. Recent research has shed light on the importance of understanding the nutritional content of our foods for optimal nutrient absorption. Strategically pairing foods can boost nutrient absorption – such as lycopene in tomatoes and olive oil – but less is known about which pairings inhibit optimal absorption, or even hinder it. For example, some of the anti-cancer benefits of tomatoes, specifically those from a compound called lycopene, could disappear when eaten with iron-rich foods, recent US research found.

The research in question may help scientists understand how cooking may have altered the evolution of our microbiomes during human prehistory. Study senior author Dr. Peter Turnbaugh, an Associate Professor of Microbiology and Immunology at UCSF, affirms that this study also raises intriguing questions about how human-associated microbes have evolved over the millennia to adapt to culinary culture and whether this could have important side effects for modern health.

The study presents the findings of a seven-year collaboration between Turnbaugh and Harvard Evolutionary Biologist Dr. Rachel Carmody. The research team analyzed the chemical changes that cooked vegetables had when fed to their mice. This revealed a list of compounds that might explain how these diets impacted the animals’ microbiomes, a question they are currently analyzing further.

The results of mice
The mice were split up into four diet groups: raw and cooked meat versus raw and cooked sweet potatoes. To the researchers’ surprise, compared to cooked meat, raw meat had no discernible effect on animal gut microbes. In contrast, raw and cooked sweet potatoes significantly altered the composition of the animals’ microbiomes, as well as microbes’ patterns of gene activity and the biologically crucial metabolic products they produced. The same experiment conducted with white potato, corn, peas, carrots and beets revealed the same results. The raw foods contained antimicrobial compounds that continued to damage or kill the mice’s intestinal bacteria.

The researchers attributed these microbial changes to two key factors. Cooked food allows the host to soak up more calories in the small intestine, leaving less for hungry microbes further down the gut. Meanwhile, many raw foods contain potent antimicrobial compounds that appear to damage certain microbes, destroying intestinal bacteria directly.

The results of humans
With this knowledge, the next research phase involved conducting the same experiments on humans. The team partnered with a Harvard-graduate professional chef to prepare comparable raw and cooked menus for a small group of research participants. The participants tried each diet for three days in randomized orders and provided stool samples. 

Those who ate a raw diet in contrast to a cooked diet were distinctly different. For Turnbaugh, this highlights the importance of considering the other components of our diet and how they influence gut bacteria.

“It was exciting to see that the impact of cooking we see in rodents is also relevant to humans. Interestingly, the specifics of how the microbiome was affected differed between the two species. We’re very interested in doing larger and longer intervention and observational studies in humans to understand the impact of longer-term dietary changes,” he concludes. 

Put that on your plate!
In line with what Turnbaugh and Carmody’s research revealed, a study from last week indicates that a plant-based diet could lead to weight loss via microbiome. With that said, awareness of digestive health is moving into the mainstream, with a visible increase of fiber, prebiotics and probiotics in NPD, according to Innova Market Insights. Moreover, digestive health is moving into the personalization space, as the personal nature of the microbiome presents game-changing potential. Just this month, for example, plant-based, functional beverages brand Rebbl has launched a new line of drinks that boast six grams of prebiotic fiber for digestive health. 

Edited by Anni Schleicher