Add in an obesity epidemic, subtract daily exercise and multiply your findings by the increasing availability of junk food near, if not in, schools.
The answer? An average 14-year-old boy today weighs 61kgs, some 24kgs (or 3st 10lb in old money) more than his counterpart in 1948.
The modern boy is, it must be said, taller too (by about five inches) but nobody disagrees that we have a serious health issue on our hands.
Just last week, the Irish School Wear Association said children as young as seven were too obese to fit into their uniforms.
Lots of anti-obesity measures have been mooted: a ‘no fry zone’ within 1 km of schools, subsidies for fruit and veg, a tax on sugary drinks and a TV ad ban on high-fat products before 9pm.
All of those measures are a step in the right direction, but there’s one very simple way to keep children on track at school – give them a nutritious, healthy lunch.
Director of Glenville Nutrition Ireland and mother-of-three Heather Leeson says there are lots of ways to squeeze extra nutrition into your child’s lunchbox.
She says making out a lunchbox plan for the week is a good idea and it’s a great way of getting children involved in the decision-making process.
Always include at least one portion of vegetables —which are high in fibre, vitamins and mineral but low in sugar — and one portion of fruit. Squeeze some lemon juice on the fruit to stop it going brown.
“Parents often tell me their children won’t eat vegetables. However, if they don’t get them, they certainly can’t eat them! Start with just a small portion. Like us, children should be aiming for five portions of veg a day,” the nutritionist says.
It’s also essential to make sure lunchboxes include a complex carbohydrate, such as wholegrain bread, a wholegrain wrap, pitta or roll, or some wholegrain pasta or rice.
Studies show that four in five Irish people are not eating enough fibre, which is essential for gut health.
Be aware, Leeson warns, that white bread has less than 50% of the fibre of wholemeal. “Two slices of wholemeal bread contain 4g of fibre but adults need at least 25g per day,” she says.
Make sure to limit processed meat, too, she adds. It’s high in salt and nitrates and has been linked to chronic diseases, such as cancer.
Instead, try tinned tuna or salmon (or a mixture of both); egg; cheese; chicken or turkey (but not processed), peanut butter or any other nut butter.
Children need to be hydrated but Leeson advises giving them water, rather than juices and smoothies that can contain a whopping five spoons of sugar per serving.
And here’s another maths riddle. If you pack seemingly healthy snacks — say, a standard carton of apple juice, a flavoured yoghurt and a cereal bar — how many spoons of sugar are you putting in your child’s lunchbox?
Those three snacks contain a staggering 14.5 teaspoons of sugar, three times the World Health Organisation’s recommended daily intake for adults.
If you’re looking for healthy treats, consider packing nut ‘power balls’, carrot and courgette muffins or oaty banana pancakes. And here are some of Heather Leeson’s ideas for school lunchboxes — and there’s isn’t a ham sambo in sight.
tinned salmon and sweetcorn wrap, hunks of cheese, an apple and carrot sticks.
Wholegrain pitta with hummus and grated carrot, natural yoghurt (add some berries to sweeten), sugar snap peas and a plum
Wholegrain bread with grated cheddar, pumpkin seeds or nuts, strawberries and cucumber sticks.
Heather Leeson will be running a lunchbox demo at the Cookery School in Donnybrook, Dublin 4 on Thursday, August 26, from 7 to 9pm. Tickets €60. For more lunchbox tips, see www.glenvillenutrition.ie