We know that foods are pleasurable. Obviously the more delicious a food is, despite whether it is "healthy" or not, the more pleasure we derive from it. This is because pleasure centres in our brains - the same areas that are targeted with things like: drugs, sex/love, personal enjoyment, become addicting for most. Chasing that feel-good "high" from certain things can be a slippery slope to travel down.
Well, a recent study really magnifies this effect has on us.
Brain imaging demonstrates a reduced neural impact of eating in obesity
This study investigated functional brain response differences to food in women with BMI either <25 kg/m2 (lean) or >35 kg/m2 (severe obesity).
Design and Methods
Thirty women, 18-65 years old, from academic medical centers participated. Baseline brain perfusion was measured with arterial spin labeling. Brain activity was measured via blood-oxygen-level-dependent functional magnetic resonance imaging in response to food cues, and appeal to cues was rated. Subjective hunger/fullness was reported pre- and post-imaging. After a standard meal, measures were repeated.
When fasting, brain perfusion did not differ significantly between groups; and both groups showed significantly increased activity in the neo- and limbic cortices and midbrain compared with baseline (P < 0.05, family-wise-error whole-brain corrected). Once fed, the lean group showed significantly decreased activation in these areas, especially the limbic cortex, whereas the group with severe obesity showed no such decreases (P < 0.05, family-wise-error whole-brain corrected). After eating, appeal ratings of food decreased only in lean women. Within groups, hunger decreased (P < 0.001) and fullness increased (P < 0.001) fasted to fed.
While fasting, brain response to food cues in women did not differ significantly despite BMI. After eating, brain activity quickly diminished in lean women but remained elevated in women with severe obesity. These brain activation findings confirm previous studies.
So what this study found was that despite just eating, obese women still viewed attractive/delicious foods as pleasurable. The non-obese women, on the other hand, didn't "activate" the pleasure centres in their brains the same way the obese women did once they were fed.
Why is this important and how can this be applied to those more prone to weight gain?
One of the most obvious tactics that could be brought from this news is don't keep junk foods in your house. Some people may have the self control to only eat ice cream or dessert every once in a while, but if you know you have a history of eating less than healthy foods, then make sure it isn't in your house. For instance, based on this research, an individual could be good with their diet all day, eating healthy and feeling satiated, yet still reach for treats at the mere sight of them.
It would be interesting to examine any possible connections between food-derived pleasure (dopamine) and the production of hunger hormones. I have written about the 2 primary hunger hormones in the past (leptin and ghrelin), but for the purpose of this blog, I will recap quick:
Leptin and Ghrelin are hunger controlling hormones, acting on the same receptors in the brain. Leptin is the "satiety" hormone, whereas ghrelin is the "hunger" hormone. When the stomach is empty, ghrelin is produced to remind our brains that we need to eat. With many, many years of evolution under our belts, human bodies have become incredibly competent at making sure we eat.
So, when we are hungry, our bodies produce ghrelin. When we have eaten our bodies produce leptin. Both hormones, as previously stated, work on the same receptors in the brain, so you are usually either one or the other - hunger or satisfied. One of the real problems that is now being discovered, however, is our body developing resistance to leptin. In fact, paradoxically, overweight and obese individuals actually have increased levels of leptin. So if an overweight person is producing more leptin than normal, yet they still continue to eat and gain weight, one could postulate that two factors could be contributing to this continual consumption of calories.
First, as previously mentioned, the leptin/ghrelin receptors become resistant to leptin, only binding to ghrelin. Similar to what we see with diabetes, with chronically increased insulin, the mechanism for glucose storage gets worn out over time.
Secondly, and linking us back to the aforementioned study, despite feeling full, our brains are still tricking us into thinking that food is needed to hit those reward and pleasure parts of the brain.
What's encouraging to know, is that although weight loss can slow down and plateau over time due to the "set point theory," if an individual is consistent enough and can fight these psychological urges to reach for junk food, then it is not impossible to attain and maintain a healthy weight.
Consistency is key...
Tyler Robbins B.Sc. CSCS
Director of Fitness
Head of CrossFit