"Based on the results of the 2008/2009 survey, 34 per cent of Canadians aged 65 or older were at nutritional risk," the agency said in its report Wednesday.
"Gaining or losing more than 10 pounds (4.5 kilograms) in the past six months and skipping meals 'almost every day' were the main drivers of nutritional risk."
Many factors affect the type of food older Canadians eat, including how often they shop, how difficult it is to cook, oral health, and how much money they have to spend.
Depression and loneliness can also be factors, especially for women aged 75 and older, the agency said.
Women were more likely than men to be at nutritional risk at 38 per cent versus 29 per cent.
Previous Canadian research suggests nutritional risk could be more common when counting vulnerable populations such as those living in nursing homes or receiving support from community agencies.
The report was based on the 2008-2009 Canadian Community Health Survey on health aging, which covered those aged 45 or older living in the 10 provinces.
Those living on reserves, full-time members of the Canadian Forces, residents of collective dwellings and those who were institutionalized were excluded.