Because it's not just about the nutrition label, but also your own individual microbiome.
bowl of yogurt with berries

Photo: Getty Images / Gabriela Tulian

You'd think if you ate a salad with grilled chicken and broccoli, it'd give you the same energy and nutrition as someone else who was eating the same meal, right? Or, if you're looking for some natural sweetness, and you choose to eat raspberries, while someone else eats blackberries, you'd also assume you'd get a very similar digestive response, as both fruits are high in fiber and have comparable levels of sugar and calories.

Yet, we're discovering that it's a bit more complicated than that, because our gut microbiomes are pretty individualized. Foods that seem to offer the same set of nutrients might not affect everyone in the same manner.

A recent study published in the journal Cell Host & Microbe, looked at 34 participants' diets and stool samples over 17 days to observe how different foods affected the gut microbiome, even when the foods they were eating were nutritionally similar. They sought to discover whether the food eaten over a period of time and how the gut responded was simple or not. The result? It was less straightforward than they thought. Foods with similar nutritional profiles did not necessarily impact the microbiome in the same way across different people.

To figure out how to measure effects of foods on the microbiome, the researchers lumped like foods together into groups. They assumed these related foods would similarly impact gut bacteria. However, they were surprised by some of the findings.

"We expected that by doing this dense sampling-where you could see what people were eating every single day and what's happening to their microbiome-we would be able to correlate dietary nutrients with specific strains of microbes, as well as account for the differences in microbiomes between people," said senior author Dan Knights of the Department of Computer Science and Engineering and the BioTechnology Institute at the University of Minnesota in a news release. "But what we found were not the strong associations we expected. We had to scratch our heads and come up with a new approach for measuring and comparing the different foods."

Foods that were in the same food group, such as kale and spinach, did produce similar results on the gut microbiomes of the participants. However, foods that were not closely related, but had similar nutritional profiles (think carrots and kale), did not match up on microbiome effects.

"Nutrition labels are human-centric," said Knight. "They don't provide much information about how the microbiome is going to change from day to day or person to person." One interesting finding. Two people who consumed Soylent, a nutritionally complete beverage, had microbiome variation throughout the study. Although two people is an extremely small sample size, it is interesting that there was more affecting their gut bacteria than just diet.

More research is needed to study the microbiome and how it is personalized to the individual, as food and nutritional ratios alone cannot predict a common response. And studying the gut is important, as it is connected to so many health factors.

"The microbiome has been linked to a broad range of human conditions, including metabolic disorders, autoimmune diseases, and infections, so there is strong motivation to manipulate the microbiome with diet as a way to influence health," Knights explained. "This study suggests that it's more complicated than just looking at dietary components like fiber and sugar. Much more research is needed before we can understand how the full range of nutrients in food affects how the microbiome responds to what we eat."

Gut health is an emerging but promising science and we can't wait to learn more about how the billions of bacteria inside us can help us get healthy.