Still much to learn about personalised nutrition

DEAR DOCTORS: I've been hearing about something called "personalised nutrition". They're saying it can help with all sorts of stuff, like depression, losing weight and even migraines. Apparently it starts with a poop sample? What's this all about?

DEAR READER: There was a time when the term "personalised nutrition" referred to dietary advice based on factors such as someone's weight, fitness level, body fat percentage, eating habits, activity levels, blood-lipid values and general health. Some of these diets narrowed their focus and targeted the participant's specific body type, blood type or even DNA.

The personalised nutrition you're asking about, also referred to as precision nutrition, takes that kind of specificity a few steps further. The companies involved are offering their clients dietary advice that they say is based on the unique composition of each individual's gut microbiome. That's the reason for the stool samples that participants are asked to provide.

Although people are conditioned to regard faecal matter with distaste, it's actually a useful diagnostic tool. About three-fourths of stool is water. The remaining 25% includes undigested fibre, as well as a wide range of metabolic products and byproducts. Traditional stool analysis evaluates factors such as colour, consistency and pH, and looks for the presence of blood, fat, protein, white blood cells, meat fibres, mucus, bile or specific organisms. These can be helpful in the diagnosis of a range of gastrointestinal disorders, certain cancers, hidden bleeding, bacterial infection and parasitic infection. Stool also contains both the living and dead microbes that colonise the gut, and that's what the new personalised nutrition is based on.

Research into the gut microbiome has revealed just how much the trillions of microorganisms living inside of us influence our physical health and mental well-being. This includes digestion, metabolism, weight loss, immune function, autoimmune disease, blood-sugar control and cardiovascular function, as well as mood, anxiety, depression and other mental health issues. There is also growing evidence that the specific makeup of each person's gut flora affects how -- and how well -- they digest and metabolise different foods. That works the other way around, too, in that the foods you eat can directly affect the health of your gut microbiome.

The idea behind gut-based personalised nutrition is that, with a detailed understanding of your specific microbiome, you can learn how to choose the foods that are best for your microbiota, and, thus, for your overall health. As you point out, a lot of promises are being made about what this newest version of personalised nutrition can achieve. These include the ability to craft diets to aid in weight loss, lower someone's blood pressure, decrease inflammation and ease gastrointestinal problems. However, it's important to note that rigorous research into these claims remains scarce at this time. Considering the wide-reaching role that the intestinal flora in our guts play in the optimal functioning of our bodies, it won't be a surprise if this approach to nutrition proves to be useful. But at this point in time, there's still a lot left to learn. Universal Features Syndicate

Dr Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health.

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