Essentially, these researchers wanted to observe if [a rapid rise in glucose and subsequent dip] actually leads to increased hunger. Further, this research provides us with more insight into just how the body works to regulate appetite and hunger, which of course could answer many of our obesity questions and issues.
The purpose of this study was to determine the effect that acute hypoglycemia has on feelings of appetite and hunger. Essentially, the researchers injected subjects with glucose. Afterwards, they measured their glucose levels to confirm they were hypoglycemic and then did a series of tests to understand each of the subject's feelings of hunger and appetite.
Why Study This
It's important to study this because many consider hypoglycemia to be a major driver of hunger and food seeking behaviors.
When you eat carbohydrate (and even protein to some extent), this carbohydrate is broken down to a simple form of sugar known as glucose, which happens to be a primary energy source for both of us. As glucose rises, so too does insulin, which drives that glucose out of the blood and into various tissues, such as organs, muscle and yes, even sometimes body fat.
It's thought that a drastic increase and, thus decrease of blood glucose (because of a large insulin spike) drives us into hypoglycemia, or low blood sugar status, which then sends signals to the brain to seek food, increasing hunger and appetite.
Essentially, these researchers wanted to observe if this actually occurs (the hunger part). Further, this research provides us with more insight into just how the body works to regulate appetite and hunger, which of course could answer many of our obesity questions and issues.
Fifteen, middle-aged men were recruited for this study and separated into either a control group or experimental group. Control group was provided with a saline solution, administered intravenously while the experimental group was given a 10% glucose intravenous injection. Additionally, 1 hour before the trial, each subject was provided with a light breakfast (cereal bar).
This study was single blind and crossover, meaning that the researchers knew which group participants were in but participants did not. Further, both groups completed each of the procedures (experimental and control), separated by a 2 week washout period.
During each procedure, blood was drawn from individuals 5 times. Once prior to the infusion, 3 times during the infusion, separated by 1 hour each and then once, 1 hour after completion of the infusion. During this time, immediately before each blood draw, subjects completed an assessment that covered many different "subjective measurements," to distract subjects from primary questions about hunger and appetite, since the subjects were unaware of the primary objective of the study.
It's important to notice that the subjects were unaware of the primary focus of the study. This is really important since many of the measurements in this study are based on subjective feelings, or how the subject actually feels. If the subjects know that the point of the study is to observe feelings of hunger and appetite, that fact alone could influence their responses. For example, many subjects want to "please" researchers and may say they are less hungry than they actually are, if they know what the researchers are actually looking for.
As we can see, in comparison to the saline solution infusion (clear circles), there was a drastic increase in both blood glucose and of course insulin, when observing the experimental group. But really, that's to be expected. However, right at the 11:00 hour mark, once insulin and blood glucose reach low points, this is around the time we should expect subjects to be getting hungry if this whole process does in fact increase hunger.
After completion of the infusions, each subject was given a test that is sort of a subject feelings test. It covers a bunch of different topics, including questions about hunger, appetite, satiety and fullness. These questions are mixed into a bunch of different questions to ensure that the subjects don't know which variables are actually being tested.
Surprisingly however, in terms of hunger and appetite, there were no differences between groups. In fact, on the hunger scale, ratings were exactly the same between groups (graph A).
Again, we see no real differences between groups. Around 9:00 we see a slight increase in feelings of satiety, however, none of these measures reach statistical significance and groups were not different from one another. A somewhat surprising finding, to say the least.
This Was a Glucose Infusion
It's extremely important to remember that this was a study using glucose infusion, not actual food. Reactions that the body has towards nutrients may be drastically different when comparing actually eating food and intravenous injections. It's very possible that had these subjects eaten actual food, their hunger responses may be different.
The primary reason they used injection is because the kinetics of digestion will be different for everyone, meaning that the speed and extent of glucose entering the blood and the subsequent insulin response will be different from person to person. By injecting, the researchers can ensure that blood glucose will rise in an expected manner.
Additionally, by injecting glucose, they can observe if feelings of hunger after the meal are specifically attributed to a rise and fall of glucose and insulin. In this case, this natural response to blood glucose did not result in hunger, differing from common belief.
Hunger May Be Attributed Elsewhere
Keep in mind that many people to in fact experience immense hunger, shortly after having meals, especially those that are high in sugar. So, somehow there is a relationship here.
My hypothesis is that when it's an actual meal being ingested, the way that nutrients are broken down and eventually enter the bloodstream may initiate other unknown hunger signals, which respond to hypoglycemia (the state after insulin removes sugar from the blood, in response to a high glucose meal.
Additionally, and this is theoretical, it's possible this has something to do with the hunger hormone, Ghrelin. Ghrelin is a hormone, secreted by cells in the gut, specifically the stomach. While these cells do secrete the hormone on a circadian rhythm, or a specific daily schedule, these cells are also sensitive to stretch.
Before a meal, you get hungry. One of the reasons is that these cells are not stretched, indicating an empty stomach. As a result, ghrelin is secreted, eventually making you hungry.
My theory is that a quick and drastic emptying of the stomach may cause issues with ghrelin secretion, due to a rapid stretch and relaxation of these cells (when these cells are stretched due to food being in the stomach, ghrelin secretion stops).
Potentially, under real circumstance when food is being consumed, a rapid excretion of food may initiate hunger signals. I mean, really it wouldn't be surprising. Fiber, for example has a hallmark attribute of slowing food removal from the stomach, which results in feelings of satiety, so if other foods act the opposite of that, it's not surprising to me that quick removal from the stomach may result in hunger.
Again, purely theoretical.
Based on the findings of this study, it's possible that a rise and fall of glucose and insulin is not the sole reason many people get hungry shortly after eating. Further, it may or may not have any influence on hunger and appetite at all.
I suggest experimenting on yourself, since you're the one that will get hungry or not. Try having one, high glycemic meal, after being fasted and then assess hunger afterwards. Then, on a separate day, do the same, with a low glycemic meal, comprised of protein, fat and carbs and then assess hunger.
Based on your findings, you can adjust your food intake to fit your individual needs.
Why This Should Matter To You
It should matter because it provides more information about how different nutrients affect feelings of hunger and appetite, which is really a million dollar question. Finding ways to control hunger is easily the most important factor in a calorie restricted diet, so understanding how to manipulate hunger may be the key to success. Further, this information provides more information with regards to glucose and insulin playing a role in hunger, as it relates to food. At least with this study, it casts doubt on the idea that insulin and blood glucose drops are the sole reason for post meal hunger.
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