Exercise before or after breakfast helps keep blood sugar in check

In obese adults, free-living exercise conducted either before or after breakfast leads to notable improvements in body composition and glycaemic control, according to a study presented at the recent 82nd Scientific Sessions by the American Diabetes Association (ADA 2022).

Both fasted and fed exercise likewise enhances the postprandial-lowering effects of interval exercise, though prebreakfast physical activity may be better in terms liver biochemistry.

“Exercise, prebreakfast, may be advantageous for people with obesity and fatty liver,” the researchers said.

After 12 weeks of a walking-based exercise program, all participants saw a significant drop in indices of body composition such as body mass, body mass index (BMI), and waist-to-hip ratio (p>0.001 for all). Similarly, levels of glycated haemoglobin decreased significantly postintervention (p=0.01). [ADA 2022, abstract 3-LB]

Of note, the degrees to which these parameters were reduced were comparable between groups. Adherence rates to pre- and postbreakfast exercise was high at 93 percent and 95 percent, respectively. The same was true for compliance (85 percent and 88 percent, respectively).

Meanwhile, only those who exercised while fasted saw a significant decline in alanine aminotransferase (ALT) levels, which dropped by 16 percent in this group (p=0.001). Walking after breakfast only induced a nonsignificant 2-percent decrease in ALT (p=0.720).

Moreover, the exercise program bore near-immediate benefits for the participants. Even after just 1 week, continuous vs interval postbreakfast walking led to a significantly lower postprandial response after dinner (p=0.047). Continuous prebreakfast exercise had a similar effect on postprandial response after lunch (p=0.064).

Such benefits were robust until the 12-week follow-up, when interval exercise correlated with significantly lower postprandial glucose responses to both lunch and dinner, as compared with baseline (p=0.008).

“Regular exercise improves insulin resistance and glycaemic control, but ‘real world’ programs are not universally effective,” the researchers said, pointing out that while laboratory-based analyses have shown pre- and postbreakfast exercise to be beneficial, “[w]hether these acute effects translate to greater changes in metabolic health with exercise training is not clear.”

The present study enrolled 34 adults with obesity (mean age 43 years, mean BMI 35.1 kg/m²) who completed 12 weeks of a walking-based exercise program, which included two continuous and two interval sessions per week. Seventeen participants were asked to perform the exercise regimen before breakfast, while the other 17 did so after.

Continuous exercise was performed at 50 percent of the participants’ max heart rate (HR), while interval training involved alternating 3-minute bursts of exercise at 85 percent and 50 percent of max HR. Each session lasted from 30–60 minutes.