“Just watch this” I say as I perform my favourite chemical demonstration, the “oscillating clock.”
After mixing a couple of colourless solutions, I tap the flask with a magic wand and the solution instantly changes to gold. Another tap with the wand and the gold becomes blue. Then I turn the wand around, tap again, and magically the colour vanishes.
To the amazement of the audience, this oscillation” can be repeated a number of times. It seems there is a clear association between the colour changes observed and tapping the flask with the wand. But of course, the wand has nothing to do with the colour change. The oscillation is the result of a complex series of chemical reactions that can be timed exactly.
Because I have done this so often, I can time the change very well and create the illusion that the wand has magical properties. I find this to be a great illustration of “association” not being the same as a “cause and effect” relationship, a very important distinction in science. For example, global warming correlates with a decrease in the number of pirates in the world and the more firemen at the scene of a fire, the more damage is done. Also, we note that students who are tutored tend to do more poorly on exams. These are all interesting associations but obviously, (I hope) there is no cause and effect relationship.
Nutritional research is plagued by the difficulty of finding cause and effect relationships because much of the data come from observational studies in which subjects are asked to fill out questionnaires about their diets and then their health status is observed. First, there is the unreliability of self-reporting, and second, such studies can only show an association, not a cause and effect relationship.
Take, for example, a study that found a positive link between consuming diet drinks and obesity. Is there something in diet drinks that leads to weight gain or are overweight people more likely to drink diet beverages? There is also an association between colon cancer and eating a lot of processed meat products. Do the processed meats cause the disease, or do people who eat processed meats consume fewer fruits and vegetables which are protective against colon cancer?
What about studies that have shown a link between consuming processed foods and weight gain? Are people who eat processed foods less active? Or are there additives or processing modalities that cause people to up their caloric intake? Such questions can only be answered by a randomized controlled trial (RCT) and such trials are notoriously difficult to carry out. But not impossible.
Researchers at the National Institutes of Health in the U.S., prompted by the increasing number of observational and epidemiological studies linking processed foods to poor health outcomes, managed to carry out such a trial. They enlisted 10 male and 10 female volunteers who agreed to spend a month in a metabolic ward where all their meals would be provided and their weight monitored. In a random order, for two weeks on each diet, they consumed either meals made with ultra-processed foods that contained an array of additives, or meals of minimally processed foods. The key was that both diets had virtually identical calorie, sugar, fat and total carbohydrate content. Subjects could eat as much or as little as they wanted.
A typical day on the “ultra-processed” diet started with a breakfast of Honey Nut Cheerios, whole milk with added fibre and a blueberry muffin with margarine. Lunch was beef ravioli, parmesan cheese, white bread, margarine, diet lemonade with fibre and oatmeal raisin cookies. For supper, steak, gravy, mashed potatoes, margarine, canned corn, diet lemonade and low-fat chocolate milk with fibre. Daily snacks provided were baked potato chips, dry roasted peanuts, cheese and peanut butter sandwich biscuits, Goldfish crackers and apple sauce.
A “minimally-processed” day would start with a breakfast of Greek yogurt parfait with strawberries, bananas, walnuts and olive oil along with apple slices dipped in freshly squeezed lemon juice. Lunch was chicken breast, apple slices, bulgur, sunflower seeds and grapes accompanied by a spinach salad with a vinaigrette of olive oil, fresh squeezed lemon juice, apple cider vinegar and ground mustard seed. Dinner consisted of roast beef and a side of rice pilaf made with basmati rice, garlic, onions, sweet peppers and olive oil. There was steamed broccoli as well as a salad of lettuce, tomatoes, cucumbers and orange slices with balsamic vinaigrette. Daily snacks were oranges, apples, raisins, almonds, and walnuts.
The results were stunning. On the ultra-processed diet, people ate about 500 calories more per day, resulting in a weight gain of two pounds over two weeks! For the first time, a study actually showed that processed foods were not only associated with but were the cause of weight gain! Next challenge is to find out why. In the meantime, this study gives me an extra line to add to my “oscillating clock” demo patter.
Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.
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