People could lose up to half a stone if they did not drive to work and used public transport or actively commuted instead, research suggests.
Experts have found that people who get the bus or train and those who walk or cycle into the office weigh less than those who get to work in private vehicles.
The new study, published on thebmj.com, examined more than 15,000 commuters' body mass index (BMI) scores.
The average BMI for men was 28 and the average BMI score for women was 27. According to NHS guidance, those with a BMI of 25 to 29.9 are considered to be overweight.
The researchers from University College London and the London School of Hygiene and Tropical Medicine, found that compared with using private transport, people who travelled by public or active transport had significantly lower BMI scores.
Men who commuted using public modes of transport or those who walked or cycled had BMI scores around one point lower than those who used private transport - equating to a difference in weight of 3kg, or almost half a stone, for the average man.
Women who used public transport or actively made their way into the office had BMI scores around 0.7 points lower than those who drive themselves in to work - equating to a difference in weight of 2.5kg, or 5.5lb, for the average woman.
The authors wrote: "Those who used active and public transport modes had a lower BMI and percentage body fat compared with those who used private transport."
"A key finding from this study is that the effects observed for public transport were very similar in size and significance to those for walking or cycling to work. This finding may have important implications for transport and health policy, as over the past decade the proportion of commuters who walk or cycle to work has remained stubbornly low outside major cities in the UK.
"Greater emphasis on encouraging a shift from private to public transport modes may plausibly have significant population health benefit and may be more acceptable to commuters."