Ever wondered why some people can eat to their heart’s content while others agonise over every calorie and still struggle to shed those stubborn kilos?
A study published in the journal Nature Food might offer some consolation for the battlers.
It adds to mounting evidence that people have uniquely individual responses to diets, showing some bodies are better at expelling calories than others, regardless of what they’ve eaten.
Healthy volunteers were given four different diets in random order over three days – under supervision so they couldn’t cheat – and daily urinary chemical metabolites were measured using molecular profiling.
The diets had varying levels of adherence to the World Health Organisation’s dietary recommendations for eating lots of fruit, vegetables and fibre, ranging from high to low compliance (low being equivalent to a fast food diet).
Each diet triggered different metabolic responses within and between individuals, and these were related to blood glucose levels, says co-author Jeremy Nicholson from from the Australian National Phenome Centre at Murdoch University.
Perhaps not surprisingly, they found that our microscopic friends played a role.
“Several of the chemicals that changed in the urine were generated by the gut bacteria,” says Nicholson, “which is consistent with the fact that people have different gut bacteria and that these bacteria can use different foods as fuel.”
Interestingly, volunteers’ metabolic profiles following the healthiest diet corresponded to those seen in lean people, while the junk food diet profiles aligned more closely with that of obese people.
So, on balance, eating healthier food is clearly better; but it’s not so black and white.
Developing a dietary metabolic score from their results, the team found that 12 out of 19 participants increased their score positively in response to the healthy diet while 13 individuals’ scores went down after the fast food diet.
The difference between the least and most calories excreted in people’s urine was four percent, equating to four calories a day. That might not sound like much, but it adds up to 1500 calories a year, or 215 grams of fat difference.
As many people would attest, such small changes can creep up over time. The researchers explain that adults gain an average of 500 grams per year, which is about 3500 calories – an excess of less than 10 calories per day.
The study adds to the growing field of precision medicine, which could help health professionals tailor people’s diets to individual metabolic profiles, helping to boost weight loss and mitigate risk of chronic diseases.
“This is a real paradigm shift in personalised nutrition research,” says co-author Gary Frost from Imperial College, UK.
“[F]or the first time we have tools that can rapidly evaluate the diet-microbiome interactions that affect individual responses to complex diet patterns in the real world.”
It might also help inspire people to change dietary habits, a notoriously difficult feat. As Nicholson suggests, knowing something is specifically good for you is more motivating, making it more likely that you’ll do something about it.
Obesity researchers would argue this still doesn’t let the fast food industry off the hook for its pervasive influence on diet, disease and health inequalities.
Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
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