3-LB: A Free-Living Walking-Based Exercise Programme Improves HbA1c in Individuals with Obesity, with Additional Benefits of Nutritional Status on Metabolic Health

Background: Regular exercise improves insulin resistance and glycaemic control, but ‘real world’ programmes are not universally effective. Laboratory studies show that post-breakfast exercise improves postprandial glucose excursions with subsequent meals while pre-breakfast exercise augments whole-body fat oxidation. Whether these acute effects translate to greater changes in metabolic health with exercise training is not clear.

Aim: To investigate if exercise before/after breakfast leads to differential improvements in metabolic health and/or postprandial glycaemic response.

Methods: Thirty-four people with obesity (43±12 y, BMI 35.1±5.1 kg/m²) undertook a 12-week walking-based programme, with two continuous and two interval sessions each week (for 30-60 min, at 50% HR_maxvs. alternating 3 min at 85% HR_max and 3 min 50% HR_max respectively) . Participants exercised before (FAST) or after (FED) breakfast (n=17 per group) . Body composition, HbA1c, blood lipids and liver transaminases (ALT/AST) were assessed pre- and post-intervention. Postprandial glucose responses were assessed in week 1 and 12 using flash glucose monitoring.

Results: Adherence (FAST: 93%, FED: 95%) and compliance (FAST: 85%, FED: 88%) was high in both groups. Body mass, BMI, waist-to-hip ratio and HbA1c decreased similarly between groups (all P >0.001, HbA1c P=0.01) . However, ALT decreased after FAST (-16%; P=0.001) , but not FED training (-2%; P=0.720) . In week 1, continuous exercise lowered postprandial responses to lunch (FAST; P=0.064) and dinner (FED; P=0.047) versus interval exercise. In week 12, the postprandial glucose responses to lunch and dinner after interval exercise were lower compared to week 1 (P=0.008) .

Conclusions: Free living exercise, pre- or post-breakfast improved body composition, glycaemic control and enhanced the postprandial-lowering effect of interval exercise but pre-breakfast exercise had a greater impact on liver biochemistry. Exercise, pre-breakfast, may be advantageous for people with obesity and fatty liver.