Meena Shah, professor in kinesiology for the Harris College of Nursing & Health Sciences, recently worked with Austin Graybeal, a Ph.D. student who graduated in May, to study the effects of a ketogenic diet on appetite. Other investigators involved in the study were Drs. Jada Willis (co-mentor) and Robyn Braun-Trocchio (committee member) and graduate students Andy Kreutzer, Petra Rack, Kamiah Moss and Garrett Augsburger. Shah shares here the driving force behind the research, what’s next and more.
To get our bearings, can you describe what a ketogenic diet is?
A ketogenic diet is very low in carbohydrates and high in fat. It is used for weight loss or treatment of certain health conditions. A ketogenic diet suppresses appetite which helps with weight loss.
What was the driving force behind the research topic that you and your student recently concluded?
Many endurance athletes, like triathletes and cyclists, have been following a ketogenic diet to improve performance. Their assumption is that the ketogenic diet allows for greater utilization of fat as a source of energy during endurance activities even though studies have found inconsistent performance results with this diet. Moreover, this approach conflicts with recommendations made by a number of professional organizations which promote a high-carbohydrate diet to enhance performance in endurance-based events.
What were you setting out to find with your research?
Athletes need to consume enough energy for optimal health and performance. Most non-elite athletes do not keep a track of their energy intake. Instead they rely on their perceptions of hunger and fullness to regulate energy intake. This may lead to insufficient energy intake especially when following an appetite suppressing diet such as the ketogenic diet. Low energy intake over a chronic basis may impair bone health and immune function. There are no studies that had compared a ketogenic versus a high-carbohydrate diet on appetite in endurance athletes. The purpose of our study was to evaluate the fasting and postprandial (post-meal) effects of a ketogenic versus a high-carbohydrate and habitual diet on subjective and objective (blood) appetite measures in endurance athletes.
How did you conduct the research?
Trained competitive cyclists and triathletes were randomly assigned to a ketogenic or a high-carbohydrate diet, for 14 days each, following their habitual diet. After completing the first diet, they crossed over to the other diet. Fasting and postprandial measures of appetite were taken after their habitual diet and immediately following each experimental diet phase.
What were your findings?
We found that both the fasting and postprandial level of the hormone that causes hunger (ghrelin) was lower and the hormone that causes fullness (glucagon-like peptide-1) was higher following the ketogenic diet versus the high-carbohydrate or the habitual diet. However, the subjective perceptions of appetite did not match with the objective measures of appetite, requiring further investigation.
What’s next?
Our research led us to conclude that extreme diets like the ketogenic or the high-carbohydrate diet are very difficult to implement. They require intense counseling and substantial dietary changes. It may be easier implement using supplements rather than major dietary changes. In future studies, we suggest evaluating the effects of exogenous ketone and high-carbohydrate supplements given over a longer period of time on appetite in endurance athletes.