Researchers found that a high-fat diet is linked to major structural and functional changes in the nasal system.
Experiments carried out on mice found those on a high-fat diet were less able to recognise a particular odour after losing 50 per cent of the brain cells that recognise the signals.
The findings, published in the Journal of Neuroscience, show diet may impact a range of human traits apart from weight.
Dr Nicolas Thiebaud, of Florida State University, said: ‘This opens up a lot of possibilities for obesity research.’
It is the first time researchers have been able to demonstrate a firm link between a bad diet and a loss of smell.
In the six-month study mice were given a high-fat daily diet, while also being taught to associate between an odour and a reward of a drink of water.
Mice given the food were slower to learn the association than a control group given their usual meals.
And when researchers introduced a new fragrance to monitor their adjustment, the mice with the high-fat diets could not rapidly adapt, demonstrating reduced ability to smell.
Fellow researcher Professor Debra Ann Fadool said: ‘Moreover, when high-fat reared mice were placed on a diet of control chow – during which they returned to normal body weight and blood chemistry – they still had reduced olfactory [smell] capacities.
‘Mice that were exposed to high-fat diets just had 50 per cent of the neurons that could operate to encode odour signals.’
The team will now begin looking at whether exercise could slow down a high-fat diet’s impact on smell.
They will also investigate if a high-sugar diet would also have the same negative effect.
Funded by the National Institutes of Health (NIH), the study comes at an important time with obesity rates at all time highs throughout the world.
According to the NIH, more than two in three adults in the US and about a third of six to 19-year-olds are considered to be overweight or obese, similar numbers to those on the UK.