We've all tried it, and that little piece of paper that comes out of it can make or ruin your day... I'm talking about the body composition machine at the local gym or pharmacy... is it accurate? are some better than others? are there better ways?

The shorter answer is: no they're not accurate, yes some are better than others, and of course there are better ways, but it's not that simple.

The "gold standards" are the Dexa Scan (using x-rays) and Plethysmography (using whole body scanner). Both are very accurate, very rare, and very expensive! Next comes Hydrostatic Weighing (full body immersion in water); it's also highly accurate, quite rare and expensive (although less than the first two).

Then come the 2 most commonly used methods: Skinfold Calipers and Bio Impedance (the wretched machine). In the hands of a trained professional, the Calipers are reasonably accurate, but do get significantly affected by water retention, skin temperature and most importantly, localized fat deposits; as such, they tend to be more accurate with people who gain/lose weight in a uniform manner (in itself a rarity).

As for the Bio Impedance machines: they are slightly less accurate than the Calipers, but tend to also be much more impacted by machine quality, hydration status, temp, and the location of fat deposits. They are notoriously bad at estimating total bodyfat in people with low fat deposits in the legs (such as men or amateur athletes).

So what to do? Here are my suggestions:

- Forget accuracy: you should just be able to monitor the "trend" in your body composition

- Always measure at the same time of day, same hydration status, temperature and conditions

- Ideally, use the Calipers if you're trained in them or have regular access to someone who is

- If using a machine, chose a high quality one (I'm a fan of Tanita) and most importantly, ALWAYS USE THE SAME MACHINE!

Using the methods above, you will still not get an accurate reading, but it doesn't matter because what you're after is "improvements in the trend" regardless of what the "actual" fat % is...