I am something of a yogurt connoisseur. I didn’t start out that way. When I first started eating yogurt several decades ago, I consumed the fat-free, aspartame-laced cartons of pink something with relish. Then a friend introduced me to regular, full-fat Greek yogurt. The texture was richer, creamier. Now, I can’t go back to the mass market, low-calorie yogurts I see in most grocery stores.
I’m not alone in my distaste for low-fat food alternatives. Many people say they can taste the difference. Food manufacturers are very interested to know exactly what causes us to sense the fat content in our foods, especially as they are under pressure from government and consumers alike to lower the calories in the foods they produce. Scientists are finding that texture plays an important role in helping us guess how much fat is in a food. By tricking our taste buds into thinking we’ve eaten more fat than we actually have, these foods might help people actually eat less.
The study participants said that the crunchier foods, which took much more effort to chew, were lower in calories than the softer foods.
Finger foods aside, most of the physical contact we have with our food is while we are chewing. This tells us whether something is crunchy or soft, how creamy it is, and more. Scientists have only recently begun to investigate the sensory information our mouths give us about the food we eat, explains Dipayan Biswas, a professor of marketing at the University of South Florida. The field is known as oral haptics, and Biswas has been studying how the mouthfeel of food affects how many calories we think it has.
“Most food is eaten with cutlery, so we only touch a food with our mouth,” Biswas says. “While we’re eating, sometimes we make calorie estimations, both subconsciously and not, and the oral haptics of a food affects this.”
With his colleagues at USF, Biswas designed a series of studies asking participants to sample foods with different textures and estimate their caloric content. The foods were identical in size and number of calories, but some were harder or crunchier than others. Almost uniformly, the study participants said that the crunchier foods, which took much more effort to chew, were lower in calories than the softer foods. This was exactly what Biswas was expecting.
Think of many of the foods we find hard and crunchy, Biswas says. Apples, carrots, and many other raw vegetables require a significant amount of chewing and are relatively low in calories. Higher fat foods, like butter, ice cream, and even avocados, are much creamier. The brain has naturally made associations between these factors, which helps drive our estimations of a food’s energy density. Of course, most of us don’t eat while sitting in a lab and consciously thinking about precisely how many calories are in our foods. So Biswas designed another study to create a more realistic setting.
This time, he asked another group of study participants to watch a series of commercials. He also gave them one of two types of brownies: One was cake-like and soft, whereas the other was crunchier. Half of each group was not told anything about the brownies, while the other half was asked about the calorie content of the brownies. After they were done, the researchers measured how much was left to determine how much each person had eaten. The results, published in the Journal of Consumer Research, show that people ate more of the soft brownies when they were not asked to think about calories, but that they ate more of the crunchy brownies when they were.
“When you talk about the hardness of a food, we associate it with healthier things,” Biswas says.
Fat is a primary contributor to a food’s creaminess. Lose too much fat, and a formerly creamy product can turn watery (skim milk, anyone?).
Other studies have found links between a food’s texture and not only the amount consumed but also how full people said they felt afterwards. Scientists at the University of Sussex in the U.K. started with a fruity yogurt smoothie, to which they added a neutral tasting thickening agent known as tara gum. After making sure that the tara gum increased perception of the drink’s thickness and creaminess in a test group, they then had a different group of people evaluate one of eight versions of the smoothie. The participants were then asked to plate up a portion of pasta that would fill them up as much as the smoothie they had just eaten. The group that drank the thick smoothie plated out the most pasta, even though the thick smoothie contained the same number of calories as the other versions. Writing in the journal Flavour, the researchers concluded that even subtle changes to a food’s texture can alter how filling we think it is.
One of the reasons that experiments like this succeed at tricking us is that fat is a primary contributor to a food’s creaminess. Lose too much fat, and a formerly creamy product can turn watery (skim milk, anyone?).
“It’s really hard to remove fat from food because fat does so many things,” says food scientist D. Julian McClements at the University of Massachusetts-Amherst. His team has discovered what it is about fat that provides a creamy taste and appearance: tiny droplets that scatter light to make a sauce look creamy. They presented their work this spring at the 247th National Meeting of the American Chemical Society in Dallas. By replacing fat with tiny beads of dietary fiber, the researchers were able to reduce the fat content in the sauce from 10 grams to two grams per serving, while simultaneously creating a sauce that had the same color and texture as the original.
Just because we rate a food as more filling or having more fat doesn’t necessarily mean we eat less of it. Increasing the satiety of low-fat foods does get around one of the major barriers of these foods, which is that people tend to rate them as less filling. But if someone is not using satiety as a cue to stop eating—and research has shown that many of us Americans aren’t—then this taste-bud tinkering may not be as effective as researchers hope.
There’s also the issue of exactly how our mouths sense dietary fats. In recent years, researchers have discovered taste receptors in the mouth that can bind to fatty acids. Although three fatty acids bound together into a triglyceride provides the fatty taste that many of us know and love, individual fatty acids do not taste pleasant. Far from helping us seek out energy-dense foods that our ancestors needed to survive, nutrition scientist Richard Mattes at Purdue University believes that our ability to detect foul-tasting fatty acids is a way to detect rancid meat. So if these receptors don’t detect triglycerides, how do we taste fat?
“I don’t think we really know yet,” Mattes says.
Perhaps other research will give us answers. Even if it does, I can’t be sure I would purchase them, nor would food manufacturers necessarily be eager to make them.
“It’s kind of a conflict of interest, trying to persuade food manufacturers to create a product that will encourage people to eat less of it,” McClements says.
The track record of low-fat foods isn’t all that impressive.
“Reduced fat foods may have created more problems than they solved,” McClements says, since people who aren’t satiated can end up consuming even more calories. Plus, the sugar that many manufacturers use to replace the fat may have actually made us less healthy.
I don’t know if I want to trick my tastebuds, and I also don’t know if they will stay tricked for long. I’ve tried all sorts of crazy things in the name of science, and I’d certainly be up for some taste tests of new products. Whether I buy them remains to be seen. In the meantime, I will be over here, enjoying every last bite of my full-fat yogurt, thank you very much.
