On Nutrition
In last week’s column, I discussed how ultraprocessed foods are defined, and the fact that the definition doesn’t take nutrition into account. Given the prevailing sense of certainty that ultraprocessed foods are a prime culprit in chronic disease, it may surprise you that there is little research-based evidence to back this up — and what evidence there is isn’t exactly robust.
That’s because almost all the evidence comes from observational studies, which can only find associations between two things — they can’t establish cause and effect. Even worse, many of those studies don’t control for variables, such as poverty, that could offer an alternate explanation for any observed associations between ultraprocessed foods and poor health. Also, these observed associations might be statistically significant, but they are rarely strong enough to be clinically significant.
One 2024 review of studies looking at associations between ultraprocessed foods and cardiometabolic risk concluded the quality of the evidence was “not satisfying,” noting that the degree of risk changed by as much as 50% depending on how ultraprocessed food intake was measured. Similarly, a 2024 review involving almost 10 million people found associations between ultraprocessed food intake and 32 health parameters — but the only association with convincing, moderate-quality evidence was between ultraprocessed food and Type 2 diabetes risk. The rest of the evidence was low or very low quality.
Recent analyses of data from the Nurses’ Health Study and Health Professional Follow-Up Study found that higher ultraprocessed food intake was associated with increased risk of cardiovascular disease and Type 2 diabetes risk in U.S. adults. However, intake of certain ultraprocessed foods — including bread, breakfast cereals, sweetened yogurt, dairy desserts and savory snacks — was associated with a lower risk of cardiovascular disease and diabetes. What about randomized controlled trials, which can show cause and effect? Well, there’s been a grand total of two. Both were very small, very short and only looked at weight gain.
So, if ultraprocessed foods do harm health, how does that happen? Unfortunately, there are many theories, but no meaningful research. Are these foods hyperpalatable, or even addictive? Are they more calorie-dense and easy to eat quickly? Do they harm the gut microbiome? Is it the high heat treatment during processing? Are contaminants or food additives to blame?
A 2021 study looked at mechanisms that might explain associations between ultraprocessed food intake and cardiovascular disease risk, but the authors primarily cited animal studies and human studies on Western-style diets — which are high in meat, sugar, saturated fats and low in fruits, vegetables and whole grains — not ultraprocessed foods per se. A 2023 review of proposed mechanisms that might explain associations between ultraprocessed foods and weight gain found no evidence of direct links.
One interesting proposed mechanism is that ultraproccessing degrades the food matrix — the components of a food plus how those components interact synergistically — of unprocessed ingredients. The authors of a 2024 review argue that the food industry should develop less-processed industrialized foods with better ingredient quality and more preserved food matrices.
For now, there are no tidy answers to the question of whether ultraprocessed foods, as they’re currently defined, harm health. I think you know that there’s a nutritional difference between a bag of cheese puffs and, say, a frozen meal that includes protein and vegetables. Cooking from scratch is great for those who have the desire, time and resources to do it. But if you don’t, nutritious “convenience foods” can bridge the gap between eating and not eating. And you do need to eat.
Carrie Dennett: CarrieOnNutrition@gmail.com. CarrieOnNutrition@gmail.com; on Instagram: @CarrieDennett. Carrie Dennett, MPH, RDN is a registered dietitian nutritionist at Nutrition By Carrie, and author of "Healthy For Your Life: A non-diet approach to optimal well-being." Visit her at nutritionbycarrie.com.