NHS Greater Glasgow and Clyde has said it does not "consistently provide" patients, visitors and staff with healthy food and drink.
While all in-house run services must comply with an existing policy to provide low-fat and sugar options, external firms are not subject to the same rules.
However, vending machines, shops, trolley services and hospitality functions will be now be affected by a new, revised policy and companies will face sanctions for not complying.
All vending machines will be required to stock only sugar-free drinks, with water and milk positioned "prominently" and 50% of stock will be made up of healthier snacks with low levels of salt, sugar and fat.
All cafes and dining rooms will be also required to adopt a pricing structure that favours healthier options. Shops will also only be allowed to promote healthy options at till points.
A board statement said: "The relationship between a diet and health status is unequivocal.
"NHSGGC does not consistently provide sufficient healthy options to enable staff, visitors and patients to easily access a healthy diet whilst on NHSGGC premises. Adoption of policy will help mitigate this risk.
"The retail policy may require national companies to change product ranges to meet criteria and may impact on commercial lease values."
It said in-house services must comply with the healthy eating policy, and this will be extended to all providers.
External providers will also face sanctions from NHSGGC if they don't follow the new policy, the board said.