Nutrition advice is often fickle. In the 1990s, nutritionists blamed fats for rising obesity rates. Then, carbohydrates became the culprit in the early 2000s. Now, the refrain is to eat whole foods and avoid ultra-processed ones. Why canât we get a straight answer on what we should be eating?
The trouble is that simply opting for foods with fewer and less-processed ingredients doesnât guarantee a healthier diet. In fact, as a recent meeting of the American Society for Nutrition in Chicago demonstrates, studies on ultra-processed food (UPF) are mixed, with researchers there often disagreeing about exactly how UPF affects our health.
For instance, at the National Cancer Institute in Maryland and her colleagues presented work at the meeting showing that people who consume more UPF had a greater risk of dying during the period of their study than those who ate fewer of these products.
Advertisement
They came to this conclusion after analysing data from more than 500,000 people in the US. Participants enrolled in the study between 1995 and 1996 and completed a questionnaire asking how frequently they ate certain foods in the past year. Following up two decades later, the researchers found that participants who ate the most UPF had a roughly 10 per cent greater chance of dying in this period, even after accounting for diet quality and body mass index.
While this suggests that UPF increases the risk of dying early, it isnât that straightforward. Other factors could explain the association. For instance, people who take the time to cook meals from scratch may also take the time to exercise or prioritise their sleep. If thatâs the case, then exercise or sleep might be the underlying factor here, not UPF. Because most studies of UPF are observational, untangling these effects is extremely difficult.
The other issue is that dietary preferences have changed in the past 30 years. For instance, the consumes significantly less beef and potatoes and significantly more chicken and cheese than they did in the 1990s. So, we canât assume that participantsâ UPF intake remained stable during the study period. Furthermore, research being carried out today canât tell us what will happen to people in 30 yearsâ time because, well, it hasnât happened yet.
But as other work presented at the meeting found, even avoiding UPF is no guarantee of health. While there isnât a universal definition of what makes a food ultra-processed, most studies refer to the , developed by Carlos Monteiro at the University of SĂŁo Paulo in Brazil. According to this system, ultra-processed foods are those made entirely from ingredients extracted from foods or synthesised in laboratories.
This definition includes foods like store-bought cookies, soft drinks and candy. But it also includes foods that can be part of a healthy diet, like wholewheat breakfast cereals, which are a good source of fibre, iron and other micronutrients, says at the University of Minnesota. âYou canât automatically dismiss ultra-processed foods as bad or unhealthy and automatically assume that non-processed foods are healthy.â
Levine and his colleagues presented research proving this point, by constructing two seven-day menus made up of similar meals. The key difference was that UPF constituted 67 per cent of the calories in one menu, but only 20 per cent in the other. Despite this, both menus provided low-quality diets, according to a commonly used metric of diet quality in the US called the Healthy Eating Index. The one with more UPF scored 44 out of 100, while the one with fewer of these products had a score of 43.
This brings up a crucial point, which is whether UPF has been linked to poorer health outcomes because it is processed or because it is simply higher in fats, sugars and salt. âIf you match [UPF] to a non-processed [food] using the same set of macronutrients â protein, fat, carbohydrate â why would one be different than the other?â says Levine. âSome people think, âOh, itâs the food additivesâ, but I donât see a lot of evidence for that.â
Until that question is answered, we canât say for sure that UPF is bad for our health. Otherwise, we risk vilifying foods that many people rely on for quick, easy and low-cost meals. For example, Levine and his colleagues found that the menu formed of mostly UPF cost about $20 less per day than the one with fewer of these products, all while providing comparable nutrients.
It is also possible to eat a healthy diet made up of mostly UPF, as a similar . at the US Department of Agriculture and her colleagues constructed a seven-day menu with a diet quality score of 86 despite 91 per cent of the calories coming from UPF.
All of this means that the question of what we should be eating to stay healthy will remain difficult to answer. âFood is a complicated structure,â says Levine. âEverybody thinks itâs simple. Itâs not.â
