Health Select Committee chair Sarah Wollaston favours a sugar tax but said the Government must also tackle promotional and marketing strategies.
Ms Wollaston said 40% of what households spend on food and drink to have at home comes from price promotions, while 37% of confectionery is bought on impulse.
The promotions are focused on sugary and unhealthy products and therefore have the effect of encouraging people to consume more rather than save money, the Tory MP said.
So in order to tackle the nation's obesity problem, which Ms Wollaston said costs the NHS around £5.1 billion a year, a tax on sugary drinks needs to be accompanied by action on promotional tools.
During a backbench debate on childhood obesity, she said: "It is a staggering fact that around 40% of what we spend on consumption of food and drink at home comes from price promotions, but unfortunately these aren't saving us as much money as we would assume, they are just encouraging us to consume more.
"Within British supermarkets a huge amount of those promotions is actually going on sugary and other unhealthy products so I would call on the Government as part of their strategy to tackle that and that we need to have a clear and level playing field that looks at rebalancing price promotions.
"But that has to be done in a way that doesn't just drive us to promoting other products such as alcohol, so a very careful evidence-based look."