How to fetch Resting energy value from HealthKit which has same value as Health App's value? - ios

Question

I'm using apple's HealthKit sample however resting energy value shown in Health app in iPhone doesn't match with the value fetched in sample app.
As per apple docs, HKQuantityTypeIdentifierBasalEnergyBurned is representing resting energy so I fetched this value from the HealthKit but the value I received doesn't match with the resting energy shown in Health App.
So I came across the apple's HealthKit sample where they are calculating resting energy based on formula:
// Calculates the user's total basal (resting) energy burn based off of their height, weight, age,
// and biological sex. If there is not enough information, return an error.
private func fetchTotalBasalBurn(completion: #escaping (HKQuantity?, Error?) -> Void)
{
let todayPredicate: NSPredicate = self.predicateForSamplesToday()
let weightType = HKQuantityType.quantityType(forIdentifier: HKQuantityTypeIdentifier.bodyMass)!
let heightType = HKQuantityType.quantityType(forIdentifier: HKQuantityTypeIdentifier.height)!
let queryWeigth: HKCompletionHandle = {
(weight, error) -> Void in
guard let weight = weight else {
completion(nil, error)
return
}
let queryHeigth: HKCompletionHandle = {
(height, error) -> Void in
if height == nil {
completion(nil, error)
return;
}
var dateOfBirth: Date!
do {
dateOfBirth = try self.healthStore!.dateOfBirth()
} catch {
completion(nil, error)
return
}
var biologicalSexObjet: HKBiologicalSexObject!
do {
biologicalSexObjet = try self.healthStore!.biologicalSex()
} catch {
completion(nil, error)
return
}
// Once we have pulled all of the information without errors, calculate the user's total basal energy burn
let basalEnergyButn: HKQuantity? = self.calculateBasalBurnTodayFromWeight(weight, height: height, dateOfBirth: dateOfBirth!, biologicalSex: biologicalSexObjet)
completion(basalEnergyButn, nil)
}
if let healthStore = self.healthStore {
healthStore.mostRecentQuantitySample(ofType: heightType, predicate: todayPredicate, completion: queryHeigth)
}
}
if let healthStore = self.healthStore {
healthStore.mostRecentQuantitySample(ofType: weightType, predicate: nil, completion: queryWeigth)
}
}
private func calculateBasalBurnTodayFromWeight(_ weight: HKQuantity?, height: HKQuantity?, dateOfBirth: Date, biologicalSex: HKBiologicalSexObject) -> HKQuantity?
{
// Only calculate Basal Metabolic Rate (BMR) if we have enough information about the user
guard let weight = weight, let height = height else {
return nil
}
// Note the difference between calling +unitFromString: vs creating a unit from a string with
// a given prefix. Both of these are equally valid, however one may be more convenient for a given
// use case.
let heightInCentimeters: Double = height.doubleValue(for: HKUnit(from:"cm"))
let weightInKilograms: Double = weight.doubleValue(for: HKUnit.gramUnit(with: HKMetricPrefix.kilo))
let nowDate = Date()
let ageComponents: DateComponents = Calendar.current.dateComponents([Calendar.Component.year], from: dateOfBirth, to: nowDate)
let ageInYears: Int = ageComponents.year!
// BMR is calculated in kilocalories per day.
let BMR: Double = self.calculateBMRFromWeight(weightInKilograms: weightInKilograms, height: heightInCentimeters, age: ageInYears, biologicalSex: biologicalSex.biologicalSex)
// Figure out how much of today has completed so we know how many kilocalories the user has burned.
let (startOfToday, endOfToday): (Date, Date) = self.datesFromToday()
let secondsInDay: TimeInterval = endOfToday.timeIntervalSince(startOfToday)
let percentOfDayComplete: Double = nowDate.timeIntervalSince(startOfToday) / secondsInDay
let kilocaloriesBurned: Double = BMR * percentOfDayComplete
let basalBurn = HKQuantity(unit: HKUnit.kilocalorie(), doubleValue: kilocaloriesBurned)
return basalBurn
}
/// Returns BMR value in kilocalories per day. Note that there are different ways of calculating the
/// BMR. In this example we chose an arbitrary function to calculate BMR based on weight, height, age,
/// and biological sex.
private func calculateBMRFromWeight(weightInKilograms: Double, height heightInCentimeters: Double, age ageInYears: Int, biologicalSex: HKBiologicalSex) -> Double
{
var BMR: Double = 0
if biologicalSex == .male {
BMR = 66.0 + (13.8 * weightInKilograms) + (5.0 * heightInCentimeters) - (6.8 * Double(ageInYears))
return BMR
}
BMR = 655 + (9.6 * weightInKilograms) + (1.8 * heightInCentimeters) - (4.7 * Double(ageInYears))
return BMR
}
I'm tried the sample app to fetch resting energy however still resting energy value shown in health app and sample app doesn't have same value.
Could any body tell me how to fetch resting energy or what is the calculation used by Health App to find resting energy?
It would be great if someone can give me some pointers on it, I'm pretty new to HealthKit.
Thanks.

Answer 1

It seems that Apple's sample is outdated. As of iOS 8 and watchOS 2 there's a call to retrieve this information in the same way that active calories are retrieved; simply change the identifier. Apple Documentation
HKObjectType.quantityType(forIdentifier: HKQuantityTypeIdentifier.basalEnergyBurned)
Don't forget to include the additional permission to read this data as well.