The Effects of Treadmill Training on Solid Meal Gastric Emptying

My name is Theresa Blickenstaff (’20), and this summer I have been privileged to work one-on-one with Dr. Emily Besecker in the Health Sciences department here at Gettysburg College. Our research is essentially looking at whether a long-term, moderate-intensity exercise program causes food to move from the stomach and into the small intestine at a different rate as compared to a control group that is not exercised. That is, when you exercise chronically at a moderate-intensity, is your body able to more efficiently move ingested materials through the digestive system? Current scientific literature is divided on this subject, and there is not a definitive answer to this question because of the variables present with exercise (for example, type, duration, and intensity of exercise) and the foodstuffs (for example, solid as opposed to liquid meals, and the nutritional composition of the food). With the results of our study, we hope to reach a more conclusive and satisfying answer to this question.

Now, you may be asking yourselves how we are going to collect our data. Have we bribed some poor souls into coming with us each day to the Jaeger fitness center and jogging on the treadmills while we stand by with our pens and clipboards, encouraging the runners with the promise of a nice meal afterwards? Well, no. What we are doing is much more complicated.

 

Our experimental model is actually the rat—the male Wistar rat, to be more precise. These rats are albino and are widely used for scientific and biological research. On account of the generous funding provided by Gettysburg College, we were able to obtain sixteen rats for use in this study, meaning that we have a large enough sample size to reach statistical significance in our results, should there be differences between the exercise and the control groups. Based on their compliance to the exercise, the rats were divided into the exercise and control groups at the beginning of the study, with eight rats in each group. Now, how exactly are we getting these cute, energetic little guys to exercise, you might ask? Well, we are using a treadmill set up in one of our labs. Just like the treadmills you are used to, this treadmill has a belt that moves at a speed that you can program. Unlike the treadmills you are probably used to, however, this treadmill has multiple lanes allowing 3-4 rats to run simultaneously (even rats enjoy a little friendly competition!).

The reason we are using a treadmill and not, say, bicycles, is that treadmills cause the rats to run or jog. This type of movement is somewhat jarring to the body, and it can cause the internal organs—including the stomach—to jostle around a bit more than any other type of exercise. As we want to see how exercise can influence the functional properties of the stomach, this type of exercise is ideal for our research.

One of my primary jobs over the course of this summer has been to exercise the rats. This is easier said than done, as I learned very quickly. See, male rats are tricky. When they are not on the treadmill, they are energetic and feisty and a general joy to be around. When they are placed on the unmoving treadmill even, they are still happy and curious. Once the treadmill belt starts moving, however, many of the rats take on whole new personalities, some of them even aging before my eyes into elderly men who just cannot—that is, will not—move forward. At times like these it is necessary for me to encourage the rats, as our study will essentially be pointless if our exercise group rats do not exercise. The tools that I have used to encourage the rats include soft brushes, flimsy cardboard, pressurized air, and delicious pancake treats. Sometimes what works for one rat will not work for another, so some creativity is definitely involved. In addition, the rats do tend to become used to certain kinds of stimulation if exposed to them for long periods of time, so I do rotate the encouragement-tools that I use. Sometimes it even just depends on the day—what works on one day may not work the next day. Generally, however, I have been able to train the rats to the point where many of them will exercise with minimal encouragement.

Each day of the week the rats are exercised for one hour at a moderate pace akin to a jog/light run. They are allowed to take short breaks on the non-moving grid at the back of the treadmill as needed. On Saturday and Sunday, the rats rest. This rest is optimal for muscle recovery but sub-optimal for compliance when working with male rats. Nevertheless, the exercise training is an eight-week period consistent with non-acute exercise programs described in the scientific literature.

 

 

Enough about running, let’s discuss breathalyzers…To collect the data on the rate at which food is passed from the stomach into the small intestine, a process known as gastric emptying, we are using the ¹³carbon-octanoic acid breath test. This test is used three times over the course of the eight weeks of treadmill training: once at the beginning to obtain a baseline reading for each rat, once in the middle of the eight weeks, and once at the end of the eight weeks. For this experiment, the rats ingest a small portion of pancake labeled with ¹³C-octanoic acid. The pancake is used because we are trying to simulate a standard solid meal; that is, one that is not too fatty and does not introduce unnecessary difficulties to the stomach’s natural process of digestion.

Once ingested, the carbon-13-octanoic acid is broken down in the stomach and passed into the small intestine. It is absorbed into the bloodstream and then travels to the liver. Here, it is oxidized and metabolized to carbon-13 CO₂, which then is taken to the lungs by the bloodstream and exhaled from the lungs. The rats are placed into individual chambers for approximately 7 hours as the infrared isotope analyzer measures the ratio of ¹³CO₂:¹²CO₂ of the rat’s exhaled breath; therefore, the breathalyzer test is a measure of gastric emptying rate. The faster the ¹³CO₂ is detected, the faster the stomach is digesting and emptying its contents.

In addition to these gastric emptying data points, I have also been measuring the body weights and food intake weights of all sixteen rats each day. These data are being used to calculate the mean energy intake (MEI) for each of the rats. This data collection will provide insights into how the body weights of the rats are changing over time, how the amount of food they are eating is changing, and how the average number of calories they are taking in relative to their body mass is changing over time. This information is of interest specifically in regards to the differences between the exercise and control groups and in ensuring that nutritional demands are being met properly.

Now that you know the basics of our summer research project, one question that is likely still on your mind is how this research is relevant. Why does the speed at which food moves through the stomach matter? It actually matters a great deal. The speed of movement influences the rate at which nutrients can be absorbed into the body and used as an energy source. For individuals living with gastric dysmotility and other disorders that cause their stomach or gastrointestinal tract to not function efficiently, the rate at which their body can access the nutrients they ingest is slowed, causing a whole host of problems of its own. The results of this study are likely to provide insight into creating treatments for senior citizens and other individuals living with gastrointestinal disorders. Rather than having to take medicine for their condition, individuals with delayed gastric emptying could potentially partake in a moderate-intensity exercise program to help treat their condition. In a world where exercise is continuing to be shown as immensely important and beneficial to the body, such a positive result to our study would be yet another jewel in exercise’s crown as the natural medicine of the body.