What prompted you to research the effect of coffee on appetite?
Matt (M): Well, my supervisor, Associate Professor Ben Desbrow, has always been involved in caffeine-related work. As part of my Master’s work in the States examining caffeine on exercise performance, I read a lot of Ben and his colleague Michael Leveritt’s (University of Queensland) work. That prompted me to come here to Australia to work with them for my PhD.
We wanted to do something a bit different than the “typical” work on caffeine and exercise, and I have considerable interest in appetite regulation, so we built up from there.
What are the aims of your research?
M: The primary aims are to examine different ways we can manipulate energy balance. The components of energy balance are energy intake (via food and beverages) and energy expenditure (through exercise, resting metabolism, and so on).
When energy balance favours energy expenditure, you create an energy deficit which can (theoretically) lead to weight loss. We are examining some daily behaviours that most people indulge in (coffee/caffeine and exercise) to see how they influence the components of energy balance.
How do you test coffee’s effect on appetite?
M: “Appetite” is a term used to describe several processes. Hunger is perhaps the most well-known term associated with appetite, and is the desire or need for something. Other “appetite” measures commonly assessed include fullness, satisfaction, and prospective food consumption.
Research participants are asked “How hungry are you” or similar and asked to mark their response on a line from 0-100 or 0-150 mm, 0 anchoring “not hungry at all” and the other end anchored by “hungrier than I have ever been”.
The primary variable we are using to assess coffee’s influence on appetite is energy intake at a test meal. To examine this, after 4.5 hours (breakfast – lunch), participants are given access to a portion of lasagne and told to eat until they feel full. This allows us to examine directly how prior coffee consumption (2.5 and 4.5 h before) influences energy intake at a meal.
In between breakfast and lunch, we are measuring gastric emptying, which is the rate that food moves from the stomach into the gut. There is some evidence that some of the components in coffee may alter gastric emptying. If gastric emptying is accelerated, individuals get hungry quicker; if it is prolonged, feelings of fullness tend to persist.
We are also examining nutrient preference and “liking” and “wanting” of particular foods in collaboration with Professor Neil King (Queensland University of Technology). This allows us to see if coffee is causing people to find high-fat, sweet, low-fat, or savoury foods more appealing. If coffee causes an increase in desire for high-fat and sweet foods, this could potentially offset any other effect coffee may have on appetite.
Finally, we are obtaining blood samples at regular intervals to examine hormones related to appetite. For example, acylated ghrelin is a hunger hormone produced by the stomach that causes increased food intake with high levels. Conversely, peptide YY and GLP-1 act in opposition as “fullness” hormones. Changes in these hormones could be linked to changes in appetite and energy intake.
How is your research going and what have been your findings so far?
M: It is early days yet. Thus far, 5 women have enrolled and completed the study. We are still actively seeking individuals. This small number of participants precludes any definitive conclusions or statistical analysis, but I can say we are seeing a decrease in energy intake of about 350 kJ (84 kcals) in the caffeinated coffee condition compared to decaffeinated coffee and the placebo trial.
Furthermore, fullness levels seem to be greater and prospective food consumption lower in the caffeine and caffeinated coffee conditions compared to decaf and placebo.
How do you think these findings can be explained?
M: I can’t say for sure yet, as we haven’t analysed any of the data aside from food intake and appetite perceptions. It is possible that we are seeing some alterations in gastric emptying, but we haven’t analysed the samples as yet. Same with the hormonal measures, although blood glucose levels have been relatively stable.
It is possible that the caffeine is exerting an effect on the brain that may be related to neurotransmitter release (dopamine and serotonin), which is linked to appetite, but this is purely speculative.
Do you think coffee’s effect on appetite is due to its caffeine content alone or do you think other substances are responsible?
M: This is one of the main reasons we have undertaken this study. Coffee is a remarkable compound. There are over 1000 components of coffee, and caffeine just happens to be the most well known. This is why we have included decaffeinated coffee, caffeinated coffee, and pure caffeine conditions – to try and tease out any components other than caffeine.
For example, chlorogenic acids, compounds found in coffee and teas, have been shown to increase GLP-1 and CCK hormone levels (“fullness” hormones), which slows gastric emptying.
Has there been any previous research into the effect of coffee on appetite and how does your research compare?
M: There have been several studies conducted – to my knowledge, 3 on coffee and 1 on caffeine. The caffeine study found that pure caffeine reduced energy intake by about 22% in men but not women 30 min after consumption (Tremblay et al. 1988).
Two of the coffee studies that examined energy intake did not observed any changes 3 h after coffee consumption in normal and overweight individuals, but did find that coffee containing 6 mg caffeine/kg body weight decreased energy intake over the course of a day using food recalls in overweight and obese individuals (Gavrieli et al. 2011; Gavrieli et al. 2013).
The final study did not measure energy intake, but reported decreased levels of hunger and increased levels of the hormone peptide YY in a caffeinated coffee condition (Greenberg and Geliebter 2012).
We hope our research expands upon previous work and may provide some mechanisms behind any changes in appetite and energy intake. We are using similar techniques, but a different protocol – participants receive a single coffee with breakfast and a second one 2 h later.
We chose this method to try to better mimic typical patterns of coffee consumption, i.e. one early in the morning and a second one mid-morning.
What impact do you hope your research will have?
M: Coffee has been linked to protective effects for a number of chronic diseases: diabetes, stroke, some forms of cancer, mental illness, and overall mortality. We aren’t totally sure why, particularly for diabetes, since caffeine can have some potentially negative acute effects on blood glucose regulation. Some of these chronic diseases are characterised by weight gain and obesity.
If coffee consumption shows positive effects on appetite, i.e. decreased feelings of hunger, increased fullness, decreased food intake, that’s another “plus” in the “pro” column for coffee consumption.
However, the research to date has only examined instant coffee with minimal or no additives. Thus, it is important to note that if a positive effect of coffee is observed, that doesn’t mean a high-fat, extra cream and sugar mocha frappuccino is going to help you lose weight – quite the opposite!
Do you have plans to research any other effects of coffee?
M: At this point, our next study is in the early planning stages. But we’re thinking along the lines of examining how pre-exercise morning coffee influences energy expenditure during and after exercise and energy intake after exercise. There is a good body of evidence that people don’t eat more after exercise bouts and that this may be explained by changes in hunger and hormones.
Most research on caffeine, coffee, and exercise has revolved around improving performance, not changes in energy expenditure or energy intake. Since many people begin their day with morning coffee and then may go for a walk or a run, it makes sense to examine how this influences their eating behaviours during the day.
Where can readers find more information about this study?
M: As we have mentioned, it is early days yet. We hope to present and publish our results near the end of the year. But if someone is reading this and lives in the Gold Coast region of Australia and wants to participate, feel free to contact me! Also, if anyone has comments or questions, you can contact me as well: [email protected]
About Matt Schubert and Associate Professor Ben Desbrow
Matt Schubert is a second-year PhD candidate in Exercise and Nutrition Science at Griffith University in Queensland, Australia and originally hails from San Diego, California.
Matt’s research is examining how common behaviours (exercise and coffee) influence energy balance, particularly appetite and energy intake. He has broad interests in exercise physiology, metabolism, and sports nutrition.
Associate Professor Ben Desbrow, PhD, APD, is a sports dietician and associate professor of Nutrition and Dietetics at Griffith University in Queensland, Australia. He completed his PhD in 2008 investigating the effects of cola beverages on endurance exercise performance.
In 1999, Ben was awarded the first Nestlé Fellowship in Sports Nutrition at the Australian Institute of Sport. Since that time he has worked with many sporting groups, including the 2000 British Olympic team and the Australian Institute of Sport Cricket Centre of Excellence.
Ben has co-authored numerous articles on caffeine use by both athletes and the general population for scientific nutrition journals. He is co-author of an upcoming book for the masses on using caffeine to improve exercise performance: Caffeine for Sports Performance