Blog for all health-conscious: Fooducate Blog - Food and the Brain: Hunger Satisfaction

Wednesday, 18 April 2012

Fooducate Blog - Food and the Brain: Hunger Satisfaction

Posted: 18 Apr 2012 05:07 AM PDT

Food and the Brain - Hunger Satisfaction

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This is a guest blog post by Jennifer Lee, Ph.D.

The regulation of how much we eat and drink is a constant battle for many of us. Our brains and bodies use a combination of signals to indicate "fullness": sensory signals (taste, smell), gastric signals (full bellies), and nutrient signals (our bodies tell our brains whether we are lacking in certain vitamins and minerals, etc.). But when something is delicious, how do we stop eating it? How do we make sure not to consume too much for our own good?

Sensory-specific satiety is defined as the decrease in the perceived pleasantness of an eaten food relative to that of an uneaten food. In other words, we are satisfied once we have had enough of something (e.g., chocolate), such that it doesn't seem as appealing as something else (e.g., salty snacks). Sensory-specific satiety affects neuron activity in areas of the brain such as the hypothalamus and orbitofrontal cortex in humans and other primates. Also, when people rate a food or drink as tasting pleasant, there is increased activation in the orbitofrontal cortex. So sensory-specific satiety is a good thing: it sends signals to the brain that help us keep from overeating. But what kinds of factors influence sensory-specific satiety?

For one, the more oral-sensory stimulation, the more satiety. The degree of oral-sensory stimulation depends on physical food properties like taste concentration and viscosity, but also depends on bite or sip size. So yes, it's true: foods with stronger flavors and scents tend to be more satisfying. And taking smaller bites can also help. Research has found that increasing oral-sensory stimulation decreases overall intake in subjects who have free-access to food and drink. For example, in one study, rats consumed 18% more orangeade when they took large sips than when they took small sips. The researchers hypothesized that this was due to the suppression of the rewarding effect of the caloric drink by sensory satiety, which is greater for consumption with small sips (lots of oral-sensory exposure) than large sips (less oral-sensory exposure).

Another factor is the issue of liquids versus solids. You might have noticed that beverages don't get a very high rating on Fooducate, and it is not necessarily because their ingredients are suspect (e.g., Naked Juice). Pure juices and smoothies, although containing good stuff, are highly caloric. Research reports that liquid foods provide a lower degree of oral-sensory stimulation than solid foods, even when the energy content is the same. Not only that, animals demonstrate less compensating responses (exercise, reduced feeding) after getting their calories from drinks compared to solid foods. Getting your calories from solid foods is always better if you're trying not to consume too much: liquids, try as they might, have a low satiating power.

Also interesting is the fact that the volume of food eaten and the degree of sensory stimulation are more relevant regarding overall intake than energy density. In other words, animal studies have shown that eating a large amount of a low-caloric food that happens to be strong in flavor (like radicchio with vinaigrette) can be just as satisfying as eating a small amount of something highly caloric (like green bean casserole). Thus, energy content does not seem to be very important for determining meal size.

Finally, diet-drinkers beware: if you're craving a sweet beverage, diet soda might not be the answer. (This is coming from a big diet soda fan, so you can trust my unbiased reporting.) Neuroimaging studies (PET, fMRI, etc.) have shown different brain responses to solutions of sugars and non-caloric sweeteners in drinkable form. It seems that tasting a caloric (sucrose) solution activates taste and reward areas in the brain more than similar-tasting non-caloric (sucralose) solutions. So perhaps Diet Coke has a lower satiating power than regular Coke.

So keep your satiety high and your energy intake down by taking smaller bites (keep the flavors in your mouth as long as possible). Smoothies are tasty, but eating whole fruits is probably best. And eat things with strong flavors- they're more likely to activate your satiety signals, and you might even eat a little less.

Information in part from "Consumption of caloric and non-caloric versions of a soft drink differentially affects brain activation during tasting," NeuroImage, 54 (2011) 1367-1374.

Jennifer Lee is a behavioral scientist who received her Ph.D. in psychobiology and learning. She is a psychology instructor, researcher, and writer in studies of human and animal behavior.