A major French study published on Monday found a link between processed food intake and a higher risk of death, but researchers cautioned that more work is needed to determine which mechanisms work.
The study, which monitored the diet of tens of thousands of French people between 2009 and 2017, found a modest association between increased consumption of processed foods – characterized as prepared or eaten versions – a risk of mortality during this period.
The results were published in the JAMA Internal Medicine published by the American Medical Association.
"We do not need to be alarmed, or to say eating a packed meal gives you a 15-fold chance of dying," warned Mathilde Tuvia, director of the Epidemiology Research Team at Paris 13, who ran the NutriNet-Sante to study with Inserm teams, Inra and CNAM.
"This is another step in understanding the relationship between processed food and health," she added.
The link between diet and disease is complex, and research results are often misinterpreted.
Last year, the same French team published a study on organic food and how it is linked to cancer risk.
A higher rate of cancer was found in people who ate less organic food – but the study did not come to the conclusion that there was a causal relationship – although this did not stop many media from emphasizing the impact of fighting organic food.
About 45,000 people over the age of 45, most of them women, participated in the latest study. Every six months they were asked to fill out three online surveys, randomly assigned for two weeks, for everything they ate or drank for 24 hours.
Seven years later, about 600 people died. The researchers then crunch the numbers and found that a 10 percent increase in the proportion of ultra processed foods in the diet corresponds to a 15 percent increase in mortality.
But Tuvia warned that instead of focusing on the figure, what is important is the existence of a statistically significant correlation – and research is one part of the growing body of work on the subject.
Specially processed foods comes under Group 4 of the NOVA Food Classification System recognized by health agencies including the Food and Agriculture Organization of the United Nations.
They have undergone several transformation processes including heating at high temperatures and the presence of additives, emulsifiers and texturizers. Many are willing to heat products rich in salt or sugar low in vitamins and fibers falling under this category.
Last year, French researchers published results from the same NutriNet-Sante study, looking at other cancers among the heavy consumers of these foods.
Since it is not possible for ethical reasons to conduct a controlled trial in which one group eats processed food, and the other is not, observational studies are the only option.
But they are necessarily flawed, depending on precise self-reporting, while there are also a myriad of other "invisible" factors in the game – although the results are adjusted to compensate for the socio-demographic criteria and the overall quality of the diet.
The burning question remains, what is it about these foods that causes negative effects on health?
One of the popular hypotheses is the presence of additives, which have been studied in laboratory conditions for cells and rats, mainly by the French National Institute for Agricultural Research (INRA)
The study is an "important contribution to literature" on the subject, said Casey Rebholz, Assistant Professor of Epidemiology at the Johns Hopkins School of Public Health told AFP, which noted that the methodology was robust despite the inherent limitations of such studies.
Another crucial message to take is that these foods are disproportionately consumed by low-income people, argued Professor Nita Forouhi of the University of Cambridge. Of the School of Clinical Medicine.
"Highly processed food consumption reflects social inequality – they are disproportionately consumed by people with lower incomes or levels of education, or those living alone," she said.
"These foods are attractive because they tend to be cheaper, they are very tasty because of the high sugar, salt and saturated fat content, widely available … there is more to be done to address these inequalities."