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A Tale of Two Twins Meets a Tale of Two Cities

We better think twice about eating ultra-processed foods.

Let’s start with the twins. Aimee and Nancy are identical twins who agreed to take part in an experiment organized by Panorama, an excellent British television documentary that often deals with scientific issues. In this case, the focus was on the impact of ultra-processed foods on health. For two weeks, Aimee consumed only ultra-processed food, while Nancy followed a diet of fresh fruits, vegetables and home-cooked meals. The meals were matched for calories, fat, sugar and fiber so that the only difference was processing.   

There is no clear definition of ultra-processed foods, but in general they come in some sort of package and are constructed from a number of food components that are blended, usually using some sort of machinery, with sugar, fat, salt and a host of additives that can include preservatives, sweeteners, emulsifiers, humectants, artificial flavours and artificial colours. Breakfast cereals, frozen pizza, instant soups, sliced white supermarket bread, hot dogs, potato chips and alas, Montreal smoked meat, are typical examples. There is no hard and fast rule, but a food that comes in a package and has a long list of ingredients including some like hydrolyzed protein, modified starch, high-fructose corn syrup, interesterified oils and hydrogenated fats that would not be found in a home kitchen can be classified as ultra-processed.  

Before and after the Panorama experiment, Aimee and Nancy underwent a battery of tests monitored by Professor Tim Spector of King’s College. The results were surprising. Aimee gained a kilo, Nancy lost weight. Aimee’s cholesterol and blood glucose went up, Nancy’s went down. And that was after just two weeks! What is it about processed food that is responsible for this nefarious effect? Usually processed foods are castigated for their fat, sugar and salt content, but in this case, the two diets were matched in terms of these components.  

Could it be a difference in texture? Studies have shown, for example, that powdered oats lead to a greater spike in blood glucose that steel-cut oats, presumably because the processing breaks down cells and leads to enhanced absorption of carbohydrates. Can it be the packaging? Phthalates, perfluoro alkyl substances (PFAS) and bisphenol A, all of which can be found in plastic or paper packaging have been blamed for all sorts of health effects. Or is it that ultra-processed foods tend to be consumed faster so that hunger satisfaction signals do not kick in and more food is consumed? It seems “fast food” applies not only to the speed with which it is served, but also to the speed with which it is downed.  

Then there is the question of the additives. Emulsifiers are one class of additives that are being scrutinized because they are ubiquitous in processed foods. They stop oil and water from separating, they make ice cream smooth, prevent bread from crumbling, and slow the formation of “white bloom” on chocolates which is the result of fat separating out. But they may be doing something else as well. Emulsifiers may disrupt our microbiome, meaning that they alter the balance of bacteria in the gut. An unhealthy microbiome has been linked with all sorts of health problems ranging from diabetes and obesity to depression and inflammatory bowel disease. The incidence of the latter, particularly in the form of Crohn’s disease and colitis has been increasing in recent years, in step with the increase in processed food consumption. In studies with mice, two popular emulsifiers, carboxymethyl cellulose (CMC) and polysorbate 80 have been shown to cause dramatic changes in gut bacteria in favour of pro-inflammatory species. Furthermore, the mucus lining of the animals’ gut thinned, allowing bacteria to invade and inflame the gut wall. Human studies are needed, but these present challenges. There are over 60 different emulsifiers in the food supply and they have different properties. Some may be injurious to the gut, some totally safe. And a randomized study would require one group of subjects consuming a totally emulsifier-free diet, which is almost impossible since thousands of foods contain emulsifiers. However, what is possible, is to have people fill out dietary questionnaires from which emulsifier intake can be estimated. They can then be followed for years to see what disease patterns emerge.  

And that takes us to the tale of two cities. In Paris, a study of over 100,000 adults coordinated by the Sorbonne’s Dr. Mathilde Touvier did just that and found that exposure to emulsifiers was associated with an increased risk of cancer. Of course, there is no nail in the coffin here, since it is possible that emulsifiers are just a marker for processed food consumption in general. Indeed, Dr. Touvier also found an association between ultra-processed foods and cancer. Now over to London. The U.K Biobank study, coordinated by researchers at Imperial College London followed close to 200,000 people for 13 years and also found an association between eating ultra-processed foods and cancer. Both studies controlled for physical activity, body mass index, calorie intake, alcohol consumption and smoking. How strong was the association? The hazard ratios are around 1.1, meaning that over the period of the study, people who ate the most processed foods compared with those who ate the least had a 10% greater risk of being diagnosed with cancer. 

The usual admonition that correlation is not the same as causation applies here. But with the potential detrimental effects of ultra-processed foods on health, there is just too much smoke for there to be no fire. So, tonight, no Montreal smoked meat for me. Although it has no emulsifiers, it does have salt, sugar, nitrites, sodium phosphate, irradiated dehydrated garlic, soy flavour and sodium erythorbate. That means it qualifies as an ultra-processed food. But I won’t swear off it forever. Tastes too good. 


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