A review of Covid-19 studies found that individuals infected with coronavirus with a BMI over 30 had greater risk for hospitalisation, more likely to be admitted to the intensive care unit, and had a higher risk of death from Covid-19.

The study led by the University of North Carolina at Chapel Hill and published in Obesity Reviews also raises concerns about the impact of obesity on the effectiveness of a future Covid-19 vaccine.

The authors said that the healthy food policies can play a supportive role in the mitigation of Covid-19 mortality and morbidity.

Researchers reviewed immunological and biomedical data to provide a detailed layout of the mechanisms and pathways that link obesity with increased risk of Covid-19 as well as an increased likelihood of developing more severe complications from the virus.

Obesity can make it harder to fight some infections

Metabolic changes caused by obesity - such as insulin resistance and inflammation - make it difficult for individuals with obesity to fight some infections, a trend that can be seen in other infectious diseases, such as influenza and hepatitis. During times of infection, uncontrolled serum glucose, which is common in individuals with hyperglycaemia, can impair immune cell function.

Co-author Melinda Beck, professor of nutrition at Gillings School of Global Public Health, said: "All of these factors can influence immune cell metabolism, which determines how bodies respond to pathogens, like the SARS-CoV-2 coronavirus. Individuals with obesity are also more likely to experience physical ailments that make fighting this disease harder, such as sleep apnea, which increases pulmonary hypertension, or a body mass index that increases difficulties in a hospital setting with intubation."

Previous work by Beck and others has demonstrated that the influenza vaccine is less effective in adults with obesity. The same may be true for a future SARS-CoV-2 vaccine, says Beck.

"However, we are not saying that the vaccine will be ineffective in populations with obesity, but rather that obesity should be considered as a modifying factor to be considered for vaccine testing," she says. "Even a less protective vaccine will still offer some level of immunity."

Working from home, limiting social visits and a reduction in everyday activities - all in an effort to stop the spread of the virus - means we're moving less than ever, says Popkin, a professor in the UNC-Chapel Hill Department of Nutrition and member of the Carolina Population Center.

The ability to access healthy foods has also taken a hit. Economic hardships put those who are already food insecure at further risk, making them more vulnerable to conditions that can arise from consuming unhealthy foods.

"We're not only at home more and experience more stress due to the pandemic, but we're also not visiting the grocery store as often, which means the demand for highly processed junk foods and sugary beverages that are less expensive and more shelf-stable has increased," he said. "These cheap, highly processed foods are high in sugar, sodium and saturated fat and laden with highly refined carbohydrates, which all increase the risk of not only excess weight gain but also key noncommunicable diseases."

Popkin, who is part of the Global Food Research Program at UNC-Chapel Hill, says the findings highlight why governments must address the underlying dietary contributors to obesity and implement strong public health policies proven to reduce obesity at a population level.

"Given the significant threat COVID-19 represents to individuals with obesity, healthy food policies can play a supportive - and especially important - role in the mitigation of COVID-19 mortality and morbidity," he said