Like 10 million others around the world, I like to watch Judge Judy. In Australia it is preceded by another American programme in which a panel of doctors advise a live audience on medical matters. I think it’s mainly a vehicle for promoting health-related products, but I’ve only ever seen the last couple of minutes so I can’t be sure.

In those closing minutes the chairman always offers a tip. The last one I heard intrigued me: Drink 5 glasses of cold water daily and lose up to 5lbs annually. In principle it makes sense. Anything cold that we ingest absorbs heat energy from our bodies to bring it up to the core body temperature of 37°C. But 5lbs (2.3kg) per year?

I made my own calculation:

• 5 x 250ml = 1,250ml = 1,250cc
• Assume that ‘cold’ means 5°C
• By definition, heating 1,250cc of water through 32 degrees requires 1,250 x 32 = 40,000 calories (or 40 kilocalories) of energy.
• 40 x 365 = 14,600kcal per year.
• Fat stores energy at the rate of 9,000kcal/kg.
• Therefore 14,600kcal is equivalent to 1.6kg of fat.

So 2.3kg seems a bit high, but it’s the right order of magnitude. And even at the rate of 1.6kg per year, starting at age 20, most people would disappear altogether before they get to 65. So there would be a big saving in pensions.