Ultra-processed foods such as ready-to-eat meats are associated with a slightly higher risk of dying prematurely from any cause, a 30-year study has determined.
The study, conducted by researchers at the Harvard T.H. Chan School of Public Health, found products such as fizzy drinks, dairy-based desserts and processed meat, poultry and seafood have the strongest links to a slightly increased mortality risk.
Ultra-processed foods include packaged baked goods and snacks, fizzy drinks, sugary cereals and ready-to-eat-or-heat products. They often contain colours, emulsifiers, flavours and other additives and are typically high in energy, added sugar, saturated fat and salt - but lack vitamins and fibre.
Published in The BMJ on Thursday (NZ time), the research noted while not all ultra-processed foods should be universally restricted, the findings do support "limiting consumption of certain types of ultra-processed food for long term health".
For their research, the team tracked the long-term health and diets of more than 100,000 US healthcare workers over an average of 34 years; 74,563 female registered nurses from 11 states in the Nurses' Health Study (1984-2018), and 39,501 male health professionals from all 50 states in the Health Professionals Follow-up Study (1986-2018). Each of the participants had no history of cancer, cardiovascular diseases or diabetes at enrolment.
Every two years participants provided information on their health and lifestyle habits, and every four years they completed a detailed food questionnaire. Overall dietary quality was also assessed using the Alternative Healthy Eating Index score.
During the study period, 48,193 deaths were recorded; 13,557 due to cancer, 11,416 due to cardiovascular diseases, 3926 due to respiratory diseases, and 6343 due to neurodegenerative diseases.
Compared with participants in the lowest quarter of ultra-processed food intake (an average of three servings per day), those in the highest quarter (an average of seven servings per day) had a 4 percent higher risk of total deaths and a 9 percent higher risk of other deaths, including an 8 percent higher risk of neurodegenerative deaths, the researchers found.
The study found no association between a higher consumption of ultra-processed food and deaths related to cancer, cardiovascular or respiratory diseases.
The association between death and intake of ultra-processed food varied across specific food groups; processed meat products showed the strongest and most consistent associations, followed by sugar-sweetened and artificially sweetened beverages, dairy-based desserts and ultra-processed breakfast food.
However, the increased risk of death may be partially explained by overall diet quality, with the researchers noting the quality of an individual's diet overall has a stronger influence on long-term health than just their consumption of ultra-processed food.
Because the study is observational, no firm conclusions can be drawn about cause and effect. Additionally, the participants were health professionals and predominantly white, which limits the generalisability of the findings, the researchers said.
However, further analyses yielded similar results, with the authors pointing to their detailed, repeated measurements, large pool of participants and long follow-up - providing greater confidence in the conclusions.
"The findings provide support for limiting consumption of certain types of ultra-processed food for long term health," the researchers said.
"Future studies are warranted to improve the classification of ultra-processed foods and confirm our findings in other populations."
In a linked editorial, New Zealand researchers from the University of Auckland pointed out that recommendations to avoid ultra-processed food may lead people to believe that other foods, such as red meat, can be frequently consumed instead.
They argued that debate about ultra-processed foods should not delay food policies that could improve health outcomes, such as warning labels on nutritionally poor foods and taxes on fizzy drinks.
