Skim milk is essentially white water, yet so many of us reach for it thinking that we’re making a healthier choice.

Obviously it has less fat than regular milk, we know that much. We can taste the difference.

But there’s a worrying niggle that it contains more sugar. Which is sort-of true. But the reality is, reduced-fat milk only has a smidge more sugar than the fattier kind.

The added sugar in dairy myth comes from the same principal behind low fat food, that the sugar replaces the fat so that it’s still got some flavour.

So let’s break it down.

There are two kinds of reduced-fat milks; light milk has had most of its fat removed and skim milk, which has practically no fat.

Per 100ml, light milk has 4.8g sugar, skim milk has 5g sugar and full fat milk has 4.7g sugar.

So there is a tiny bit more sugar in reduced-fat milks, but the difference is negligible.

The reason that their sugar content is slightly higher isn’t because they’ve added extra in for flavour, it’s because when the fat is skimmed off, the proportion of natural sugar in milk goes up a tad.

“When they take the fat out of the milk, what you’re left with is a more concentrated source of everything else,” advanced accredited practising dietitian Melanie McGrice tells Coach .

“So that means that you’ve got more protein, more water, more nutrients such as calcium and you also have more lactose, which is the natural milk sugar.”

Based on that principal, it also explains why reduced-fat natural yoghurts have a higher sugar content than their full fat counterparts.

Think of the natural sugars found in milk as the ones found in fruit, they’re nothing to worry about. What you want to limit is added sugar, which manufacturers add to processed foods to make them taste better.

McGrice realises that it can be hard for people to differentiate between natural sugar and added sugar, but it’s easy to spot when it comes to milk.

“If you look on the ingredients list of a container of milk, most of the time you will see that there are no other ingredients — it will say ‘Ingredients: Milk’,” she says.

“Sometimes they might add some vitamin D, but usually it’s just milk.”

And while we’re at it, keep in mind that full-fat milk isn’t too far off the reduced-fat kinds.

“Even whole milk is only four per cent fat. When we compare that to something like a doughnut, which is 30 per cent fat, it’s really not high in fat at all,” McGrice says.

“The definition of ‘low fat’ is anything under three per cent fat, so [whole milk] just misses the cut-off.”