by Lisa Keilhofer

What’s on the menu today? How cooking impacts our microbiome

Do cooked foods change the microbiome?
Do cooked foods change the microbiome? (Picture: © lassedesignen -

What shall we eat? This question has not been answered for the last decades. Historically speaking, the answer has always been “whatever we can get”, while today’s affluent society is in the luxurious position to choose from different options. But is it really pure luxury? At least, what we consume has a great influence on our wellbeing.

Among the countless diet guides of the modern world, there are also some – self-proclaimed or whatever qualified – experts who plead for the paleo diet (that is focusing on raw fruit and vegetables). The idea behind is that our genes alter a lot slower than our consumption habits do and that the human organism is not prepared yet for the “new” achievement of cooking.

At the same time, the history of human development teaches us that the invention of fire and cooking made food more easily digestible and set free energy for other improvements – enhanced brain capacities, among others. More about: >>> The intelligent stomach - our second brain.

Why do we cook at all?

To decide whether or not cooking food “makes sense” or if we are maybe going to far as we do in so many cases of modern amenities, let us have a closer look, at why humans heat their food, at all. The most trivial answer of all is, of course, that a warm meal warms you up from the inside – a fact that especially inhabitants of northern countries highly appreciate in the cold season. Hygienically speaking, heating things destroys germs and other unpleasant dwellers in and on our food. Especially for infants, children, old and pregnant people, cooking is indeed a good measure to prevent illness. And at last, cooking changes the structure and chemical composition of substances and makes consumed food digestible more easily or at all.

Does it make a difference if food is cooked or not?

There is little to no scientific research on if or how cooked vs. raw food influences our system. A research team with senior author PhD Peter Turnbaugh of the University of California at San Francisco and PhD Rachel Carmody of the Harvard University, tried to find out if cooking alters our microbiome. The simple answer is: yes, it does. Cooking influences our microbiome in regards to composition and diversity. Unfortunately, this is about the only distinct conclusion that can be drawn, so far. In fact, the impact that cooking has on our microbiome seems to be a pretty complex process.

Let’s have a closer look at the results of the study, published in September 2019 in >>> Nature Microbiology. The study was carried out on mice and men, as >>> preceding studies suggested a high comparability of the impacts.

Mice on raw potatoes diet: decreasing diversity of the microbiome

If we put mice on a diet of raw sweet potatoes, the diversity of their microbiomes decreases. Also, the total number of bacteria in their gut showed a slight decrease. In addition, there appeared to be a small increase in Bacteroidetes bacteria. Those are needed for the degradation of glycan, a polysaccharide found in raw sweet potatoes, for example. To find out what factor is actually responsible for the change in the microbiomes, the scientists made lists containing information on level of starch and degradability. In a next step, the mice were fed raw and cooked white potatoes, beets, carrots, corn, and beans. The ingredients of the food were exactly catalogued to find out possible correlations of intake and change in the microbiome. The result: the gavage of raw vs. cooked white potatoes showed a similar result as the sweet potato diet, but apart from that a generalization could not been drawn on all the other foods. This is also true for meat: the gavage of cooked vs. raw meat did not significantly alter the microbiome.

The conclusion Turnbaugh draws, is that the reason for cooked diet being partially so different from raw diet, is to be found in the starch that it not so easy to digest. This result is interesting for mice, but on the other hand, white and sweet potatoes are traditionally exclusively found in the cooked version in human kitchen, as the raw version is not digestible.

During the tests, mice fed on raw foods appeared to lose weight and the theory was that the loss in weight had some correlation with the altered microbiome. As a cross test, the mice fed with cooked diet were implanted the “raw food microbiome”. But the astonishing outcome was that these mice even gained in weight. The team is still searching for an answer to this seemingly contradictory outcome.

How did the humans react?

Subsequently to the mice tests, a group of five healthy women and three healthy men aged 24 through 40 years, was put on a diet of raw vs. cooked meals of the same content and their stool was analyzed. First, there appears to be a clear difference between a “raw food microbiome” and a “cooked food microbiome”, similar to the differences found in mice, but the chance of microbiota was distinct in the rodents. The study again showed that men and mice are only very limited comparable.

The results leave room for many open questions. The main result of the study is that cooking indeed does make a difference and that these differences vary greatly from food to food. Also, it turned out that rodents are only very limited comparable to humans and not ideally suitably for future studies. Last, the test group of only eight persons is far too little to draw reliable conclusions.

The team around Turnbaugh and Carmody hopes to be able to use future insights in the matter in nutrition therapy. But from today’s perspective, there is still a lot of research to be done.

Lisa Keilhofer
Lisa Keilhofer

Lisa Keilhofer studied at the University of Regensburg. She works in internationalization and as a freelance editor.

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