What did they do?
They compared the Mediterranean diet to a typical American “Fast Food” diet. The Mediterranean diet is rich in fruits, vegetables, fish, fibre and “good” fats (mono- and poly- unsaturated). On the other hand, the Fast Food diet includes a lot of red meat (like burgers), fries and soda – full of the “bad” fats (saturated), processed simple sugars, high in cholesterol and low in fruits, vegetables and fibre.
Why did they do it?
The Mediterranean diet is associated with improved heart health and a reduced incidence of heart disease. On the contrary, the Fast Food diet is associated with an increased risk of heart disease, Type II diabetes and obesity.
Those with serious chronic conditions have a unique “microbial signature”, compared to their healthy counterparts. The research team wanted to see what effects the different diets would have on the gut microbiome.
How did they do it?
- Ten healthy people (18-25 years old) were selected
- The researchers looked at what bacteria were present at baseline (before the dietary interventions) for each individual. They then were able to compare this to the bacteria present during the different stages of the study
- The participants were given both the Mediterranean diet and the Fast Food diet in a random order for four days each, with a four day break (“wash-out”) in between. The diets differed considerably in their nutritional composition and components. The Mediterranean diet was provided to each participant and the Fast Food diet was bought from the same fast-food chain for all participants.
- They collected blood and poop samples from each of the participants and these were analysed for different markers
What did they find?
On average, most participants responded to the diets in a specific way. However, the level to which this happened varied on an individual level.
The researchers saw that the types of bacteria present in the gut changed quickly in response to the different diets. On the Mediterranean diet, there was a growth of fibre-loving bacteria. These included Lachnospira, Roseburia and Butyricicocus. However, on the Fast Food diet, there was an increase in some less beneficial bugs. These included, Bilophila, Collinsella and Alistipes. These are typically associated with low fibre and high fat intake.
It appeared in the study that an individual’s response to a diet depends on what bacteria are present in the gut initially. Certain individuals may be more prone to the growth of certain bacteria in response to diet. They also found that the activity of the bacteria was altered within a short time period.
A number of compounds changed between the two diets. For example, levels of betaine (an anti-inflammatory amino acid) and hippuric acid (negatively correlated with metabolic syndrome) were both increased on the Mediterranean diet.
On average, the levels of tryptophan increased on the Fast Food diet but decreased on the Mediterranean diet. Tryptophan is an essential amino acid, with a number of important roles in the body. However, an imbalance of this amino acid has been associated with a number of diseases, including inflammatory bowel disease (IBD) and cardiovascular disease. The researchers felt the differences were solely related to diet but one hypothesis was that the tryptophan from red meat (from the Fast Food diet) is more readily absorbed than tryptophan from foods on the Mediterranean diet.
So, what does this all mean?
Diet has a rapid and generally consistent effect on our gut microbes (for most of us). The bacteria we have in our guts will somewhat dictate how we respond to dietary changes. If a particular bug is absent, potentially you might not see a certain effect. In the study, after 4 days of eating a diet high in red meat, saturated fat and processed sugar, the participants’ microbiomes shifted towards a profile consistent with certain chronic diseases. Conversely, eating a diet high in fibre, fresh fruit and vegetables can help you create a more beneficial microbial mix, associated with many health benefits.
Our gut microbes play a major role in health and disease. Feeding them appropriately can have a positive impact on our long-term health. A reminder that “you are what you eat.”
