One third of respondents increased alcohol intake and 20 per cent drank more sugary drinks.
"With the restaurants, fast-food chains and takeaway outlets closed, we wondered if more home-cooked meals would result in healthier eating over the lockdown," Gerritsen said.
"But independent grocers, and fruit and vegetable stores were also closed which may have limited options for buying healthy food."
Supermarkets, dairies and petrol stations, which remained open during the lockdown, "are characterised by heavy marketing of ultra-processed foods which can have excessive energy and are high in added sugar and salt".
New Zealanders weren't the only ones who have struggled to eat healthily during the pandemic.
Research from around the world shows time at home, boredom, and heightened stress leads to more snacking, partly because food is constantly available at home.
Health messages from the government during lockdown focused on infection control, physical exercise, mental health, accessing health care, and family violence.
Another researcher in the Covid Kai Survey team, Dr Lisa Te Morenga, said: "Public health advice could include the importance of nutrition for immunity, how to prepare healthy home-cooked meals, and tips to avoid eating in response to stress."
During future lockdowns, the Government could allow independent grocers to stay open; restrict the marketing and promotion of unhealthy food, alcohol, and sugary drinks; and subsidise healthy foods like fruits and vegetables, especially for families on low-incomes, the authors say.
Gerritsen said the study - whose participants were recruited through social media posts and email newsletters of health and food-related organisations - came with some limitations.
"A survey that is representative of the population was not able to be conducted during the lockdown," she said.
"The online survey was biased toward those who are more likely to be on social media, with high literacy, and interested in food issues."
