People who eat around double the amount of fruit and vegetables, grains, pulses, olive oil and who enjoy potatoes, end up slimmer than those who prefer a diet heavy in meat, eggs, dairy and animal fats.
The study, presented at the European Congress on Obesity in Porto, Portugal, examined data for 16,181 people who were not obese at the start of the research, and who were scored according to their dietary habits.
A plant-based diet including vegetables, fruits, grains, nuts, olive oil, legumes and potatoes received positive scores, while animal foods such as meat, animal fats, dairy, eggs, fish and seafood received negative scores.
Over the course of 10 years, 584 people became obese.
Analysis showed that people in the top fifth for adhering to the plant-based diet were 43% less likely to become obese than those in the bottom fifth, who ate much more meat, dairy and fewer vegetables and fruit.
Those in the top fifth ate an average of 731g per day of vegetables (just over nine portions), compared to 348g among those in the bottom fifth.
They also enjoyed 531g per day of fruit (almost seven portions), compared to 191g in the lowest fifth, and 26g per day (almost two tablespoons) of olive oil compared to 12g in the lowest fifth.
Those on the plant-based diet ate 142g of meat per day (around the weight of a chicken breast), compared to 196g in the lowest fifth and also ate more potatoes, less dairy and fewer eggs.
Fish intake was similar between the groups.
Professor Maira Bes-Rastrollo, from the University of Navarra in Spain, who presented the study, said plant-based foods contained more fibre and helped people feel fuller for longer.