Waistline is a calorie counter and customizable macro tracking app (open-data, open source, crowd sourced)
When the integration is enabled, a new button appears on the upper right corner, and allows 2 ways sync between Waistline and Intervals.icu:
- Calories spent during physical activities are pulled from ICU and displayed in the diary
- Calories consumed are pushed to ICU and will show in the wellness data section of the corresponding day
More details here