Why drinking coconut water during exercise is coco-nuts.
To say that coconut water’s popularity has increased in the last decade is somewhat of an understatement. For a drink that didn’t really exist in bottled form at the turn of the century, the growth in consumption since then has been meteoric. In the 9 years between 2004 and 2013, sales climbed from virtually zero to $400m in the US alone, and it’s suggested that the global industry could be worth up to $1bn now.
When you boil it down, coconut water’s popularity seems to be down to a number of things. Firstly, it’s viewed as ‘natural’ (even though some popular products are made from concentrates plus additives). It’s also lower in sugar than most sodas. Perhaps most importantly, numerous endorsements from Hollywood A-listers have made it ‘cool’. It also contains a significant amount of electrolytes, and this has led to some heralding it as a ‘natural sports drink’.
A quick straw poll in our office revealed that most of us don’t mind a drop of coconut water, it’s got an interesting blend of sour and sweetness to the flavour and works well in smoothies, as well as some more creative cocktails. However, coconut water-based products are definitely not a replacement for your typical sports drink. The simple reason is that it just doesn’t put back in what you’re losing in your sweat. Sweat contains predominantly water and sodium, with only small amounts of potassium, calcium, and magnesium. Perspiration is drawn into your sweat glands from the extracellular fluid (ECF) in your body, which is heavy in sodium, and much lighter on the other ions. Simple really.
Replacing some of that lost sodium helps to maintain (or at least reduce the effect of the drop in) ECF and blood volume during heavy sweating. This is the main function of a sports drink. It’s no surprise that it’s sodium that’s the main component in many sports drinks - we've even dedicated an entire post about why it's so important for athletes! Coconut water, by contrast, is extremely high in potassium but very low in sodium (see the table below). It’s actually more like the composition of intracellular fluid (ICF) in the body, rather than ECF.
So, if you’re just swigging coconut water as a pleasant day-to-day drink, rather than when you’re working out, that’s fine. Potassium can actually lower blood pressure in some people and assist with intra-cellular rehydration, so a sensible amount can be useful when recovering from the sort of mild dehydration not associated with training. However, if you’re using it to try to maintain hydration levels when sweating heavily, the lack of sodium means that coconut water simply comes up way short.
On top of the lack of sodium, there’s a genuine concern that drinking lots of coconut water could be unhealthy, or even dangerous. And by ‘lots’, I mean the kind of volumes many athletes are consuming in hot/humid conditions.
Renowned heart surgeon Dr. Raj Jutley (one of Precision Hydration's co-founders) flagged up a potential issue with coconut water quite a few years ago when the trend was starting to get some traction. He knows all about what excess potassium can do to the heart because surgeons routinely use an infusion of potassium into the heart to stop it beating when they need to operate on it. His fear was that, if consumed in excessive amounts, the potassium in coconut water could potentially cause a condition called hyperkalemia (elevated blood potassium levels), leading to arrhythmias where the heart does not beat properly.
A case study published in 2014 reported an incident involving a healthy male tennis player who was hospitalised for 10 days with hyperkalemia drank 8 small 11oz (310ml) bottles of coconut water during a match. He took in about 5.5 grams of potassium, with the daily recommended intake being around 4.7 grams. His condition could have been fatal if left untreated. Luckily, in the end, he made a good recovery. But it’s scary when you consider that he ‘only’ drank about 2.5 litres of coconut water over the course of a tennis match. Of course, this example is an extreme case, but it’s certainly not an isolated incident.
Now, to be clear, I’m not saying that you should give up coconut water. Unless you’re drinking it in very large quantities, it’s unlikely to make you unwell or kill you. In fact, if the popular urban myth is to believed, you’re probably a lot more likely to be bumped off by a falling coconut than by drinking the contents of a few! What I’m saying is that the lack of sodium and abundance of potassium in coconut water means it’s just not an alternative to your sports drink when you’re sweating a lot.