The popularity of paleo-style diets that encourage people to load up on meat, nuts and "good fats", along with "clean eating" trends are calling into question whether calorie tracking is really the be-all-and-end-all of our weight loss or weight gain journeys.
It's causing some to question whether the calorie has had its day, and we should be using our wearables to track other metrics to gauge our health, wellbeing and even weight instead.
Essential reading: Best calorie tracking tech and apps
Nick Mitchell, founder of Ultimate Performance Fitness cleared up some common sense myths about the humble calorie:
"Not all calories are created equal, and some are infinitely better for your body than others (think Paleo as a general guideline here). But anyone who tells you calories don't count fails to understand basic mathematics."
Here at Wareable we're interested in how regular consumers can use wearable activity trackers (and their accompanying apps) to paint an accurate picture of calorie intake versus calorie burn.
The calorie tracking tech minefield
You don't have to read up on this area for long to realise there are a lot of different factors at play and countless data points to consider.
When I first started writing about medical and health tech a few years back, the general consensus seemed to be that accurate calorie tracking relied on a lot of equipment and calibration in a controlled setting. This involved using an indirect calorimetry device that analyses the oxygen and carbon dioxide levels in your breath.
So have the new era of wearable trackers that promise to help us lose weight and track calorie intake and burn really come on in leaps and bounds?
Well, the answer is complicated and despite many brands using similar terminology when they describe their calorie tracking smarts, there are some subtle and not-so-subtle differences.
Depending on who you speak to, there are different ideas about how to accurately track calorific burn. Many believe that armed with specific metrics you can get a good idea about the amount of energy you're expending, these include your HR rest (heart rate when you're resting), HR max (maximum heart rate when you're working out hard), VO2 max (the maximum rate at which your heart, lungs, and muscles use oxygen during exercise), weight, age and gender.
Relying on algorithms
That's all well and good for the new biometric sensor laden wearables out there, but most affordable, mass-market trackers on the market estimate resting caloric burn using info about your weight, height and gender. They then rely on added sensors to estimate how many calories you're burning when you're active.
Let's take a look at Fitbit's calorie tracking (or should we say guessing) system:
"Your basal metabolic rate (BMR) is the rate at which you burn calories at rest just to maintain vital body functions like breathing, heartbeat, and brain activity. Your BMR usually accounts for at least half of the calories you burn in a day and is estimated based on the physical data you entered when you set up your account: gender, age, height, and weight.
The calorie burn estimate that Fitbit provides takes into account your BMR, the activity recorded by your tracker, and any activities you log manually. If your tracker measures heart rate, the calorie burn estimate also takes heart rate into account."
The only differences are that some trackers are packing more sensors than others, which gives you a slightly more accurate picture. For instance, the Basis Peak can track heart rate and takes these metrics into account along with stats about skin temperature and perspiration rate that it claims makes it one of the more advanced options on the market.
So which are the most useful? Well, in their early study of Polar wearables, Crouter, Albright and Bassett point to the importance of heart rate monitoring tech: "The advantage of using HR is that it is a physiological parameter that can detect changes in exercise intensity even when the movement patterns differ greatly," they wrote.
And it's this focus on finding out more about not just how long you're running or working out for, but the intensity and the type of activity, all factors which subtly affect energy expenditure. The problem is that even armed with this extra data Crouter, Albright and Bassett found that the margin for error could still be between 2 and 33 percent depending on the individual. That's a massive discrepancy.
Human error, environment and screwing up
And that opens up another discussion: the personal and environmental factors at play.
Although wearables built to measure heart rate are generally considered to give much more accurate indications of energy expenditure they can be massively effected by countless personal and ambient factors. Emotional stress, hydration levels and current training status can massively throw off heart rate stats. A study in the European Journal of Clinical Nutrition even found that caffeine intake can skew heart rate results.
Another issue is if you're using information about energy expenditure to inform your diet, you'll soon realise there's a huge margin of error.
There have been countless studies over recent years that point to the fact most people are prone to massively underestimating the calories in their food. Granted, food databases like MyFitnessPal aim to remove some of these headaches, but there's still no way you're going to guarantee that your intake and expenditure are 100 percent accurate. Which is always a problem when a system relies on any kind of self-reported metrics.
Given that most wearables on the market can only keep an eye on a handful of metrics, and many of these could be skewed by all kinds of circumstances, suggests that what consumer-facing wearables can provide us with isn't really calorie tracking. But calorie estimating.
Sometimes it might be a pretty accurate estimate, but it's important to remember that although it may be effective, it's not gospel.
So the big question is, does this matter? Well, for general improvement or to provide you with a ballpark figure, no.
But inaccurate information about calories could actually derail many peoples' progress. Especially if they're using it as an excuse to eat more. Or on the other end of the spectrum, an excuse to skip lunch. Both of which aren't likely to leave anyone feeling healthier, fitter and happier in the long run.
Wearable tech brands should realise that it may be good and well to shout about tracking calorie intake and burn, but if combining the tech and algorithms aren't getting people the results they want then they're bound to look elsewhere or ditch wearable tracking tech altogether. And customers should be aware of the margin of error too. And while wearables do a great job of raising awareness of our intake, it's important not to get to precriptive.
Of course there have been plenty of success stories. But given how new much of this tech is, and how few people have used them consistently over a long period of time, it's too early to tell whether the margin of error right now doesn't matter or whether it's just a waste of time.