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The Satiety Index in Dieting

Learning Objectives
1. Distinguish between satiety and satiation
2. Explain how the satiety index is determined
3. Describe the effects of alcohol and caffeine on appetite
4. Explain the role water plays in satiety
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Audio Transcript

Intro: Welcome to Obesity: A Disease, the official Obesity Medicine Association podcast exploring the many facets of the disease of obesity. In this episode we'll be hearing from obesity medicine specialist and OMA clinical education director, Dr Nicholas Pennings. Joining him is Dr Justin Tondt, MD. Dr Tondt is one of the authors of The Obesity Algorithm and was a presenter at the 2021 OMA Fall Obesity Summit. Today our speakers discuss the strengths and limitations of the satiety index. Obesity: A Disease podcast, is brought to you by the Obesity Medicine Association, a clinical leader in obesity medicine.

Nicholas Pennings, MD: Eat less, exercise more or in North Carolina, the expression is eat smart, move more. Either way, the emphasis here is on calories in and calories out. What is fundamentally flawed in that thinking is that all calories are the same, and that calories from fat, from protein, and from carbohydrates are just calories and all we need to do is eat less of them. The physiologic and metabolic effects of fats, protein, and carbohydrates are not all the same, nor is the effect of different combinations of those macronutrients. When the body is in a negative caloric balance, the physiologic responses to increase hunger signals and decrease satiety signals. Different macronutrients, and different combinations of macronutrients will have variable effects on hunger and satiety with certain foods more likely to produce satiation and or satiety.

Hi, I'm Dr Nick Pennings, chair of family medicine at Campbell University School of Osteopathic Medicine and executive director of clinical education at the Obesity Medicine Association. With me today is Justin Tondt, MD. Dr Tondt is an assistant professor in the Department of Family and Community Medicine at Eastern Virginia Medical School. He's one of the authors of The Obesity Algorithm and a presenter at the 2021 OMA Fall Obesity Summit. His presentation was titled The Satiety Index in Dieting. Welcome, Dr Tondt.

Alright, there are a lot of different terms used in the discussion of appetite regulation--hunger, satiety, satiation, cravings, and desire to eat are just some of the commonly used terms. In your talk, you focus on the difference between satiety and satiation. What is the difference between those two terms and why is it important to make it a distinction?

Justin Tondt, MD: So satiation is the feeling of fullness that causes someone to finish a meal. Whereas satiety is the feeling of fullness that lasts from when a meal ends until the next meal begins. I'd say the difference between these is important to research settings so we can better identify and learn about the different mechanisms involved. However, in real life these often blur together and our goal is usually just simply to minimize hunger.

Pennings: And when you’re talking to patients or doing a history, do you focus so some people seem not to be full while they’re eating…they just kind of keep going and then some people get hungry earlier. Do you try to make that distinction in clinical practice?

Tondt: Sometimes it can be useful. As I said, often they blur together. But there are some distinctions that you can make. So sometimes beverages, they can provide a good amount of satiation, make you feel full pretty quick, but then they don't last very long, so…one area and another could be more protein-based foods often have a better satiety and last.

Pennings: Tell us more about the satiety index how long has it been around, and how is the satiety index determined?

Tondt: Sure, the satiety index was first published by Holt in 1995, so it's been around for a little over 25 years now. The research team studied participants by putting together portions of 240-calorie portions of food, and then they would measure appetite ratings every 15 minutes after giving the food on a standardized appetite-rating scale, and so that's how it was determined…the measurements…and then they would add up the area under the curve for those appetite scores and divide that by the same error in the curve for the reference food which was white bread similar to the glycemic index and all multiplied by 100, just like the glycemic index. Overall, they tested about 38 foods.

Pennings: And so this is based then on different people's perceptions of feeling full and how quickly they felt full or how long they felt full.

Tondt: Yeah, so this was based off of their perception. How they filled out their appetite rating on a scale over every 15 minutes over 2 hours. So it's their feelings of fullness.

Pennings: Do you know, is there wide variability in satiety response and satiety index on an individual basis? Were some foods more likely to create satiety in certain individuals but not others?

Tondt: That's an interesting question. I have not seen any research that on that that I'm aware of. I don't think that would be the case.

Pennings: When I first heard about the satiety index, my first thought was that it would be similar but inversely related to the glycemic index. My rationale was that if food had a high glycemic index, meaning it was quickly converted to glucose, it would have a low satiety effect, as that glucose would be quickly disposed into tissues leaving the body looking for more calories. In your presentation you listed some foods like oranges and potatoes as high on the satiety index, but they're also high in the glycemic index. What enables those foods that are known to convert to glucose fairly quickly produce a high level of satiety?

Tondt: And so, as I talked about in my talk, there's many factors that play into society, but I think the largest one at play here is probably energy density. So the idea is that the stomach has stretch receptors, which transmit a signal through the vagus nerve to the brain to give a feeling of fulness. So if you have a given number of calories, as in the satiety index, your portion of calories, foods that have a bigger volume or mass per those calories, they're able to stretch out the stomach more and provide a greater signals to the brain of fullness. There's also some evidence for and against the glycemic index and glycemic load playing a role. Overall, evidence on that isn't that strong, so I'm not convinced that's playing a role.

Pennings: Yes, and so that kind of speaks to the concept of volumetrics, right, where the volume of the food is going to create a certain level of satiety independent of its calorie content, right? So a large volume, small calories is going to create more of a satiety effect and that's what you think is contributing to the satiety. Index of those foods?

Tondt: Yeah, yeah, I mean, that's the idea of what volumetrics is based off, like you're saying. And…definitely energy density and the volume of food definitely plays a role, just not the only role in satiety.

Pennings: Like many things, there's multiple variables that influence, especially in obesity medicine, right? Many over-the-counter dietary supplements include caffeine, presumably to increase calorie burn. What are the effects of caffeine on appetite and metabolism?

Tondt: As caffeine is a stimulant, I would expect it to acutely decrease appetite and lead to weight loss similar to other stimulants. And to some extent the research data does support that, but people tend to compensate by eating more food later in the day if they have coffee in the morning. And people often develop a tolerance to caffeine's effects. So overall, it doesn't really seem to play a large role in decreasing appetite and weight loss, at least compared to other stimulants. As for the metabolism, a high-dose caffeine can lead to a small increase in fat oxidation, but the significance of that is kind of questionable, because if you're not burning more calories or more fat than you're spending, you're just kind of shifting where your energy is coming from, so you maybe oxidizing more fat and less glucose.

Pennings: OK. So water is commonly recommended as part of a healthy lifestyle change. Does water have any impact on appetite? In particular, if you're having water with a meal, is it better to drink water before you eat? During your meal? After your meal? In between meals?

Tondt: I'd say water's pretty important. Drinking water has a relatively small impact on appetite because in general beverages don't really have a good effect on suppressing appetite. As I mentioned before, they can kind of make you feel full pretty quickly because they stretch out the stomach, but the effect doesn't last very long because they have a pretty fast motility through the system, but I would still say drinking water is beneficial in terms that it has no calories in it. So if you look at like satiety per the number of calories, that is a pretty large ratio because there are no calories in it. I'd say the more important part of water, though, is actually eating foods that have water in it. That goes back to the energy density that we were talking about before. That's probably the largest factor of what makes decreased energy density. But in either case, when to have the water, it would be good at any time in meal, but the earlier the better. So you can kind of get more of that stretching of the stomach and feel fuller early on and then…so you don't eat as much over the whole course of the meal.

Pennings: Yeah, so that high water content foods tend to then, again, have a lower calorie content and expand that stomach and promote satiety by that mechanism. I've also heard that thirst can be perceived as hunger and so that quenching thirst can sometimes lessen hunger, or that there may be some confusion around that. Have you ever seen anything with respect to that?

Tondt: Yeah, that can happen. I'd say as long as you're hydrated you should be OK with that because you don't necessarily have to drink the water, like If you have a whole bunch of water in your food, you still may be hydrated. If that makes sense.

Pennings: So there's a humorous saying, “I love cooking with wine. Sometimes I even add it to the food.” Cocktails before meals are a common occurrence for many. What is the effect of alcohol on appetite and on food choices?

Tondt: That's a great question. In research settings, alcohol as a macronutrient is about as satiating as carbohydrates and fats. But in a real-world setting, alcohol is usually not very satiating. As I mentioned before, it's usually as a beverage, but as you said, it could be used in cooking too, but I'd say the other main part is that it causes disinhibition, so people are more likely to make bad food choices or overeat. And speaking in particular to people that are trying to lose weight, if you only have a certain amount of calories, I know we talked before about it's not all about calories in calories out, but you still have a limited amount of stuff you can have in a day. And it doesn't provide…alcohol doesn't provide a lot of micronutrients, vitamins, and minerals, so it may not be the best way to get your total [crosstalk]…

Pennings: And it often comes with a lot of calories as well with certain drinks that may be high in sugar and… particularly in sugar. What about exercise? What effect does exercise have on satiety, and does it differ according to the type, intensity, or duration?

Tondt: Exercise is a bit complicated. There's good evidence that it acutely decreases appetite and increases satiety. However, over the long term, at least several weeks or longer than that, people tend to compensate for this. The exact reason why isn't known, but it may be related to non-exercise activity thermogenesis, particularly with people that are doing aerobic exercise, they may just…may have less spontaneous movement throughout the rest of the day, kind of compensating for the activity that they did voluntarily. But in terms of intensity, higher intensity, so things like strength training usually are better at suppressing appetite than lower intensity things like endurance, training or walking. And higher intensity things also generally have less compensation than lower intensity activities. But the flip side is longer duration is also more…better for appetite as well, partially because there's a psychological component to appetite, so. If you're sitting around and get bored, you may get hungry and want to eat. Whereas if you're walking or keeping busy all day you're just not thinking about eating.

Pennings: One of the things that people don't recognize is how easy it is to eat the calories you just burn when you're exercising. That an extra helping at dinnertime or a couple of cupcakes or something like that can counter an hour workout…that you tend to perceive that you're burning a lot more calories and you feel justified, maybe, in eating something that could offset all that calorie burn.

Tondt: Yeah, definitely, I mean in an hour workout like you're saying, you may burn like 100 to 300 calories.

Pennings: Yeah, right.

Tondt: Like you said, a cupcake, it's not a whole lot. And when people look at the exercise equipment at like a gym, if you look at the ellipticals or treadmills or something, they usually tell you more calories than you would be burning just from the exercise, because they include the basal metabolism add calories as well. So you would have burning those calories regardless.

Pennings: So I wasn't aware of that, so that that they're including your basal metabolic rate or resting metabolic rate plus your activity rate, that's interesting. So lastly, when discussing obesity treatment with your patients, what's your favorite bit of advice?

Tondt: I often find that patients feel defeated, so my favorite piece of advice is for them to not blame themselves. Like you said before, people often been told to eat less, and that's not sustainable in the long term because hunger increases. So I think trying to help people cope with strategies to eat more satiating foods is better.

Pennings: Well, thank you very much for joining us today for this podcast to hear Dr Tondt's presentation. You can find it in the OMA Academy. It is The Satiety Index in Dieting. Thank you for being with us today and thank you for your insights.

Tondt: Thank you for having me.

Outro: [outro music] Thank you for listening to this episode of Obesity: A Disease. For more information about obesity medicine podcasts and other valuable resources from the clinical leaders in obesity medicine, please visit www.obesitymedicine.org/podcast. If you enjoyed this episode and want to listen regularly, head over to iTunes where you can subscribe, rate, and leave us a much-appreciated review. The views expressed in this episode are those of the host and guest, and do not necessarily represent the opinions, beliefs or policies of the Obesity Medicine Association or its members. Please join us again for our next episode of Obesity: A Disease.

Audio Information

© 2022 Obesity Medicine Association. All Rights Reserved.

Disclosure Statement: Unless noted, all individuals in control of content reported no relevant financial relationships.

If applicable, all relevant financial relationships have been mitigated.

Participation Statement: Upon completion of this activity, learners will receive a Participation Certificate.


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