AIM: To explore how average weekly running distance, combined with changes in diet habits and reason to take up running, influence fat mass.
METHODS: Fat mass was assessed by bioelectrical impedance at baseline and after 12 months among 538 novice runners included in a 1--year observational prospective follow--up study. During follow--up, running distance for each participant was quantified continuously by GPS while reason to take up running and change in diet was assessed trough web--based questionnaires. Loss of fat mass was compared between runners exceeding an average of 5 kilometers per week and those running less.
RESULTS: Among those taking up running to lose weight, running >5 kilometers per week in average over 1--year combined with a positive change in diet reduced the fat mass of --5.58 kilogram [--8.69;--2.46], p <0.001. Compared with those also running >5 kilometers per week but without changes in their diet the mean difference in fat mass between groups was --3.81 kg [--5.96; --1.66], p < 0.001. A difference of --3.55 kg [--5.69; --1.41], p < 0.001 was found when comparing with those running ˂5 kilometers per week and changed diet positively.
CONCLUSION: An average running distance more than 5 kilometers per week in runners who took up running to loose weight combined with a positive change in diet, may be more effective to reduce fat mass over a 1--year period among novice runners than running without diet changes. Importantly, randomized controlled trials are needed to finally document the effect of self--structured diet changes.