Scotland has been warned it is hurtling towards an "epidemic of larger waistlines and increased cancer risk" fuelled by people's love of sweet treats and fast food.
A new study by Cancer Research UK found that more than a third of Scots ate confectionary at least once a day.
It warned that being overweight was the single biggest cause of preventable cancer after smoking.
The Scottish government said it was committed to tackling obesity.
Thirteen types of cancer, including bowel, breast and pancreatic, are linked to a person's weight, according to Cancer Research UK.
The charity said its research revealed that 39% of Scots consumed confectionery at least once a day and almost a fifth (18%) of Scots have a soft drink which contained sugar at least once a day.
About two-thirds (65%) of adults in Scotland and more than one quarter (28%) of children were found to be overweight or obese.
The findings, for Cancer Research UK's Scale Down Cancer campaign, were based on a YouGov survey of 3,293 UK adults, 513 in Scotland, carried out between 24 February and 8 March 2016.
Cancer Research UK is calling on the Scottish government to act to make it easier to shop healthily and improve the diets of Scots.
The charity's cancer prevention expert Professor Linda Bauld, who is based at the University of Stirling, said: "Scotland's sweet tooth is a huge worry for the health of the nation.
"Sugar should form no more than 5% of our diet but, on average, both adults and children in Scotland consume much more than this.
"Too much sugar in our diet can lead to weight gain - which is not just linked to cancer, but also the risk of heart disease, type 2 diabetes, stroke and tooth decay.
"If left unchecked, obesity will lead to a rising tide in ill health, including cancers, and become a crippling burden on the NHS."
The charity said foods on promotion accounted for about 40% of all expenditure on food and drink consumed at home.
It wants restrictions on supermarket multi-buy discounts on foods that are high in sugar, fat and salt to form part of measures in the expected Scottish government strategy to improve diets.
The charity said half (52%) of adults in Scotland had a ready meal once a week or more and 16% eat fast food or a takeaway at least once a week.
Prof Bauld added: "The Scottish government can, and must, do more to make it easier to shop healthily and serve up a better future for our young people. We need urgent action now to prevent thousands of cancers in the future."
Food Standards Scotland said it supported the charity's call for action but it cautioned that there was no "single silver bullet" to Scotland's obesity problem.
Its head of nutrition science and policy, Heather Peace, said: "We all need to recognise there is a problem and everyone, including consumers, the food and drink industry, retailers, media and government has a part to play in finding a solution."
Public Health Minister Aileen Campbell said: "We are committed to tackling Scotland's obesity problems and will consult on our new diet and obesity strategy this year, building on our wide range of activity to make it easier for people to be more active, eat less and eat better.
"We're investing £12m over five years to 2017 on a range of programmes to specifically tackle the nation's poor diet, including engaging with the food and drink industry on action to offer healthier choices, rebalance promotions, and reformulate products with a focus on reducing calories, salt, fats and added sugar."