A 20% tax on sugary drinks would reduce the number of obese adults in the UK by 180,000, say researchers writing in the British Medical Journal.
The impact would be greatest in the under-30s, the Oxford and Reading university study suggests.
But some groups say a tax is misguided and simplistic, and would not have an impact on older age groups who might benefit most from losing weight.
Earlier this year doctors called for a soft drinks tax to reduce sugar intake.
Sugar-sweetened drinks, when taken regularly, have been shown to increase the risk of obesity, diabetes and tooth decay.
A typical sugary drink can contain six to 15 teaspoons of sugar. One teaspoon of sugar is equivalent to 4g of sugar or 16 calories.
A 20% tax would add about 12p to the price of a 330ml can of fizzy drink bought in a supermarket or about 40p to the cost of two-litre bottle.
The researchers in this study estimated that such a tax could cut drinks purchases by 15% and lead to a reduced energy intake of 28 calories per person per week.
Overall, they estimated that such a tax would reduce the number of obese UK adults by 1.3% and the number of overweight adults by 0.9%.