TRE, HIIT and HbA1c

Introduction

A couple of readers spotted the paper for review in this week’s note – thank you. The paper was called “Time-restricted eating and exercise training improve HbA1c and body composition in women with overweight/obesity: A randomized controlled trial” (Ref 1).

The three abbreviations in the title of this note are time-restricted eating (TRE), high intensity interval training (HIIT) and hemoglobin A1c (HbA1c), although the latter is usually known by its abbreviation – HbA1c. HbA1c is a measure of glucose in the blood stream over the previous three months.

Time restricted eating (TRE) is, as the name suggests, a dietary intervention whereby eating takes place in a window of time. There are different options for TRE, related to how long the window of eating is and when it takes place during the day. E.g., TRE may involve not eating before noon each day or not eating after a certain time. It may involve eating within an 8-hour window etc. In this paper, time restricted eating was defined as eating within a window of fewer than or equal to 10 hours and with the last meal consumed no later than 20.00 hours.

High intensity interval training (HIIT) is performed as short, repeated bouts of high-intensity aerobic exercise separated by low-intensity breaks. It can involve many different exercises e.g., cycling, swimming, jogging, star jumps etc and the intense period, break period and number of repetitions can vary. In this paper, HIIT was defined as three supervised treadmill sessions per week. Specifically, two of the weekly sessions consisted of 4 x 4-minute work bouts at 90–95% maximal heart rate (HRmax), separated by 3 minutes of moderate-intensity recovery. The third session comprised 10 x 1-min work bouts at greater than or equal to 90% of HRmax separated by 1 minute low-intensity recovery. All sessions included a 10-minute warm up at 60–70% HRmax, and a 3-minute cool-down, for a total scheduled exercise time of 108 minutes per week.

The background to the paper was given as – it is known that time-restricted eating (TRE) and high intensity interval training (HIIT) can improve cardiometabolic health, but it is not known if combing these interventions can induce further improvements.