Only an estimated 36.1% inhabitants are of an ideal weight or underweight, taken as a body-mass index of lower than 25 and a ratio of height to waist of 0.5.
Dr Rosa Ortega of the university’s nutrition department says this ratio is a more effective method of calculation than BMI, although if body-mass index alone was taken into account, the number of people overweight or obese would fall from 63.1% to 53.1%.
Men are more likely to be overweight than women, with only 28.9% of males compared with 42.7% of females being of an ideal size for their height, or lower.
Age is also a factor – only 20% of Spanish residents in their 40s or older is of an ideal weight, or underweight.
Excess weight has gradually been creeping up on people in Spain since the mid-1980s, says the Spanish Nutrition Foundation.
And even in the last decade and a half, the number of Spanish residents carrying too much body weight has risen sharply.
The most recent figures available, based purely upon body-mass index – but which would be higher if height-waist ratio were taken into account – date back to 2013, when 26% of people in Spain were found to be clinically obese.
This has risen from 15% in 2002, according to the study which was recently published in BioMed Research International magazine.
Some of the problem is thought to be related to the Mediterranean diet losing the battle against fast food and processed food, and the fact that the latest generation of adults has little experience in home cooking, unlike their mothers – given that until fairly recently, the job of feeding the family fell to the woman of the house – and are more likely to eat out, purchase takeaways or live off ready meals and frozen food.
Spanish family culture means children are not brought up to be expected to do their fair share of the housework, meaning that by the time they leave home – especially nowadays with young adults moving further afield to find work rather than living close to their families – they are often ill-prepared for day-to-day housekeeping.