Calories: Comprehensive list of wearables that measure your calories

How do wearable devices track your calories?

Firstly, smartwatches calculate your basal metabolic rate (BMR, often used interchangeably with resting metabolic rate) - the number of calories required for breathing and thinking i.e. doing sedentary things. To get your BMR, fitness trackers take in your height, weight, age, and gender on the assumption that taller people require more energy to go about their day to day business and men burn more calories daily. BMR tends to account for about half of the calories that you burn in a day.

Secondly, smartwatches also capture your ‘active calories; which is the amount of calories that you burn throughout the day only while doing physical, non sedentary activities such as walking or working out. These calories are calculated based on the activity level, personal indicators (including height, age, weight) and your heart rate.

Garmin devices actually use a series of different methods to calculate how many calories users have burned and the accuracy varies based on which method is used. Methods include the New Leaf VO2 test profile, Firstbeat algorithm, and the FR60 Heart Rate algorithm. One of the most important variables in these calculations is VO2 or oxygen consumption as it was identified by the American College of Sports Medicine as key to measuring activity intensity. Calculations of VO2 rely on a combination of heart rate, respiration rate derived from HRV, and other variables depending on the analytic engine used.

What are calories?

A calorie is a unit of energy. Historically, scientists have defined it as a unit of energy that could come from a variety of sources including coal and gas. However, when we refer to it in the nutritional sense, all types of food - fats, proteins, carbs, or sugar - are important sources of calories, which we need to survive and function.

There are two types of calorie:

1. A small calorie (cal) is the amount of energy required to raise the temperature of 1 gram (g) of water by 1º Celsius (º C).
2. A large calorie (kcal) is the amount of energy required to raise 1 kilogram (kg) of water by 1º C. It is also known as a kilocalorie.

1kcal is equal to 1,000 cal.

Different macronutrients have different amounts of calories. One gram of protein has 4 kcal, one gram of carbohydrates has 4kcal whilst a gram of fat has 9 kcal.

The amount of calories a person needs in a day depends on the individual's activity level and resting metabolic rate. According to the National Institute of Health a middle-aged moderately active female should consume 2,000 calories per day whilst a middle-aged moderately active male should consume 2,400 to 2,600 calories per day.

However other important factors that determine recommended calorie intake include overall health, physical activity demands, sex, weight, height, body shape.

Why is it important to track our calories?

There are a range of different benefits we can enjoy by tracking calories. Two key benefits are:

1. You can learn how much you actually consume and burn. By realising how much we are consuming and burning, we can figure out how much different activities burn and also what eating habits we should keep, or drop
2. Make better choices. By keeping track of our calories in / out we can remain accountable to ourselves and track our progress better. By learning how much we are burning, we can adjust our consumption to meet our goals

However, simply counting calories in and out will not give information about the nutrients that we are consuming. It's important also to balance the breakdown of carbs, fats and proteins according to our goals.

For example, an olympic weightlifter will likely have a more protein-rich diet in order to fuel muscle growth and recovery whilst an endurance athlete might opt for more carbs.

Through the Terra API, we provide connections to a range of different devices so that your users can track their steps.

Below is a list of the wearables that track calories today:

• Garmin Fenix series, Venu series, Lily, Approach, Vivoactive, Forerunner series, Instinct series, Enduro, Descent series, Mk2 series, Epix, Tactix series, D2 series, Vivomove series, Approach series, Vivofit, Marq series, Quatix series
• Fitbit Versa series, Charge series, Inspire 2, Sense, Luxe, Ace 3,
• Apple Watch all series
• Polar Grit X Pro, Grit X, Ignite series, M430, Unite, Vantage series,
• Withings ScanWatch series, Steel HR, Move ECG
• Oura ring Gen 3, Gen 2
• Samsung Galaxy Watch all series, Galaxy Fit2
• Suunto 9 range, 7 range, 5 range, 5 peak, 3 range, Ambit3, Core range, Traverse
• Wahoo Elemnt Rival Multisport GPS watch
• Xiaomi Mi Watch