When you really want to eat something specific right away--that's a legit food craving. We commonly crave things that are sweet, starchy, high fat, or fast foods. 

But what causes these cravings? There are two schools of thought. The first one is that having a nutrient deficiency induces your body to seek out the food that contains that nutrient. This idea is pretty common on the internet. The second school of thought is that cravings are more psychological and due to conditioning. For example, when you sit down to watch a movie you crave popcorn. Not because you're lacking nutrients, but because you're conditioned to eat popcorn when you watch a movie. 

Which one of these is true (or, *more* true)? Let's find out! The study we're dissecting in this episode is a meta analysis of eight randomized control trials and it gives us some pretty good insight into which of these two ideas seems to be a stronger force for food cravings.

*** RESOURCES AND LINKS ***

For more information on Leesa, visit:
https://leesaklich.com/

For more information on Lindsay, visit:
https://www.lindsaycarvalho.com/

*** TRANSCRIPT ***


[00:00:00.330] - Intro/Outro

rEATsearch is a podcast that explores current nutritional research and health studies. Our lawyer says we have to let you know that this podcast is for entertainment, educational, and informative purposes only. If you have any health questions, see your doctor or licensed health professional.

I think this is a good topic, too. I'm glad you picked this one, although, I mean, I say that about every one I'm like, "this topic is so cool."

We're still so new to this. So they're all new.

I know. I know. I love that the novelty isn't wearing off.

Before we get started, can I talk about some business?

Yes.

Yeah, I heard back from Strub's.

Oh my gosh.

I emailed them.

Amazing.

And Strub's Original dill pickles are fermented, like we talked about, remember we can see the cloudiness in the brine, and they are not pasteurized. So, as far as I can tell, based on that, they are raw, live-cultured pickles. And they are delicious.

They are.

And I am not getting money for this. This is just a long time Strub's dill pickle lover.

As am I. And the fact that it's refrigerated as well, which also shows that it's not pasteurized. So, that's good. Maybe one day the podcast will get big enough that we would get sponsors such as them.

 That would be nice. But yeah, I just thought I'd share.

That is super cool.

They did reply, which I was quite impressed with, and they're Canadian, they're a Canadian product. So if you're anywhere else and you can't get them. Haha, we have better pickles. But yeah, go try Strub's dill pickles. They are really, really yummy and they have tons of garlic in them which is also . . . fermented garlic is actually really good for you as well. We could do a whole other podcast on garlic.

Could we not? Yes.

But as of right now it's definitely something you can get to help support your immune system, which is good.

That's so cool that they got back to you.

I know. I was quite happy when I saw that.

Yay.

All right.

Awesome.

So what are we talking about today, Leesa?

So today, we are going to talk about food cravings like, "oh my gosh, I need to eat this specific thing right now." So the study that I pulled up is called Extended Calorie Restriction Suppresses Overall and Specific Food Cravings, a Systematic Review and Meta-Analysis. Which you can read because I've linked to it in the show notes. So you can enjoy it.

Oh fantastic, and is this a free article online?

It is

Even better. I love when they do that.

Not paywalled. So it is accessible by everyone. Basically, in a nutshell, this study wants to know whether being on a calorie-restricted diet can affect your food cravings. Because there's two schools of thought on food cravings, which we'll get into in just a few minutes. But I like this study because, it's a systematic review, meta-analysis. So it's a review of several studies. So the evidence is pretty strong. If we get into a teeny bit of the history first, this study was done in 2017. And, of course, the data on whether food cravings increase or decrease during dieting is all over the map.

Yeah.

People who are dieting, they're restricting calories. Some people have more cravings for these foods. Some people have fewer cravings for these foods. What does the overall big picture look like? This was a meta-analysis of eight studies. And because it was a meta-analysis of several studies, we're ranking it as a 7 out of 7 on our scale, which again, is going to be linked in the notes. So it has got pretty strong findings.

Yeah, just want to reiterate, meta-analysis is the top of the pyramid. It is the best of the best because they are able to pull the data from published papers and combine it all together into the study to do their fancy statistical analysis. And so we just have so many more data points, which is why it holds so much more significance.

Exactly, exactly. I'll jump to the conclusion before we dive into how they did it and what this all means. Basically, in a nutshell, what they found when they looked at multiple different studies is that reducing calories or restricting calories is associated with reduced cravings.

Oh.

I know, reduced cravings. Again, the data was all over the map. So they took a bunch of it and looked at it all in one lens and they found that when people are eating less, they actually, eventually crave less. And we'll go into how this all came to be.

Okay, I'm already starting to get questions in my head so I can't wait.

Yeah, yeah. Do you want me to keep going or do you want to ask?

Nope, keep going. I want to wait 'til there's a better time.

Okay, cool. So what they did was . . . these were people with obesity.

Okay.

And, just as a little aside, as a health writer, we don't refer to people with obesity as being "obese people," anymore. So, people are not their diseases.

Yes.

The new way of talking about people is, they are not their diseases. They have diseases. So I'm very glad that this study was speaking about "people with obesity" and not "obese people."

Well because language is just really important. How we describe and how we use words and what words we're using have a big impact. So that's good. But I'm grateful that they were doing that.

Right, exactly. So, the researchers looked at studies of people with obesity who were on calorie-restricted diets for 12 weeks or longer. And they self-measured their food cravings before and after their diets. There's a standard measure called the Food Craving Inventory, where people are asked a bunch of questions, and they rate the answers from 1-5 on how strongly they feel these things and act on their cravings. This was actually an experiment. This is not an observational study, this is an experimental study. So, obviously, the people who are looking at all of these studies had to find the studies that actually used this metric and the criteria.

Now, cravings . . what do we crave? Well, of course, we crave overall food--we crave food in general, calories and nutrients. Exactly. We crave food. But there's also a very specific cravings for things like--and I'm sure you can agree--sweets.

Yeah.

High fat.

Yeah.

High starch.

Oh yeah.

Fast food. These are all the standard cravings that most people experience at some time throughout their lives.

Yeah.

A food craving, like the "cravingness" of the craving, is not just the desire for food. It's not just, "I'm hungry." It's defined as a "frequent, intense and irresistible desire to consume a particular type of food."

Okay.

So it is very specific. Because it is on a specific type of food, and it is intense.

Yes.

It's not like, "I'm kinda hungry."

I think we can all attest to that.

Right, exactly. It's good to have definitions when you're doing a study because then everybody's on the same page.

I agree.

And then, in general, the research shows that people who have overweight and people who have obesity. People who have a higher body mass index, which, again, BMI is used in this case just as a measure, not as a judgment. They tend to have higher levels of cravings for foods. In particular energy-dense, higher fat foods. This is a physiological body's reaction and the cravings tend to be stronger. And they sometimes also crave sweet foods, starchy food, fast food. We all crave all of them. But the studies do show that there is increased craving with increasing weight. Which is very interesting when clinicians, as health professionals, as nutrition pros, are trying to help people and to really understand where people are coming from physiologically and psychologically and everywhere. So, if you think about cravings, and this is where the study was really interesting, because there's kind of two schools of thoughts on the different reasons why we have cravings.

Yes.

One is called the "deficiency theory" [deficiency model].

Yes.

And this one is very common and popular on the Internet. Where, if people need a nutrient, they're deficient in something, then their body will naturally have them gravitate to the foods that have that nutrient. That it's some kind of innate craving to meet a deficiency or an actual physiological need.

Yeah.

Right. You've heard of this, this is very common.

Oh yeah, you see different images and graphics all over all social media, including Pinterest and stuff like that. I think the one that comes to mind most is if you're craving sweets, you're low in magnesium.

Oh, yes, I've seen that. The chocolate magnesium connection.

Yeah. That's just the one that comes to mind thinking about it.

Right. Yeah. I've seen those. And that is part of the body of research that shows that there's a link with deficiency. And that's only one theory [model] because remember, before this study was done, the data was all over the place. I mean, it's still all over the place. But this data tries to put it all together.

The other theory [model] is called the "conditioning theory" [conditioning model]. And by conditioning theory [model], it's more that food cravings occur because there are certain psychological connections that we make between certain foods at certain times. For example, maybe we go to watch a movie, we crave popcorn.

Yeah. I think that's a very good example.

Exactly, right? I love me my popcorn, to be honest. So, there are two different ways [of thinking]. How much of food cravings are physical deficiency needs versus how much are psychological? What about even comfort foods like, "oh my gosh, I feel bad, I'm going to make myself a soup that used to make me feel better as a kid?" Kind of thing, right?

Oh, yeah, there's definitely a connection there. And it's funny, there is something to that theory [model], because when you look at comfort foods, which is typically what we need when we're not feeling our best and we need some type of emotional support. But, you look culture to culture, comfort foods change from culture to culture. Which tells you there's that psychological connection to something that happened previously to us. And that's where that connection is coming from.

Exactly. So we have two very relatable [examples], we've all probably experienced both of them, different ideas on where these come from. And really, the bottom line here is it's probably a combination of both on some levels and there may be more factors involved. The human body is infinitely complex. So this is not about who's right and who's wrong. It's how much weight do they both have with each other? And that's what this study was trying to look at.

Yeah. And normally when we have different theories [hypotheses], it seems like, it's a combination, you know, it really depends on so many different factors. So it's not that one is right and one is definitely wrong, it's how do they interplay together? It really comes down to that mental state and all of these different [ones], like hormonal factors, memory, neurotransmitters, etc. Everything kind of coming together, and creating this response.

Right. And that's kind of what this study is going to be showing.

Oh, I'm jumping [ahead].

That's exactly it--it's multifactorial, right? And that's the whole point. That's why we look at things from the big picture. . . We're looking at several studies together. So, now there's evidence for both. Of course, we've all probably experienced both on some level for different cravings. What they did was . . . And I wanted to just spend a couple of minutes on how they chose their studies. Because this is really important when you're looking at a meta-analysis. It is not just the fact they had eight studies, but how do they pick which eight studies they were going to look at? And this is always super important to look for when you're looking in research. What they did was. . . And, of course. They wrote it all up in their methods section so it can be recreated by anybody who wants to do this exact same thing and double-checked their responses, which is part of the scientific process. You put stuff out there and how you did it. And you know what? Other people can double-check it andsee if get the same results.

That's a really important point. I'm glad that you brought that up because that is a huge part of the scientific process. It has to be repeatable by somebody other than the person running the initial experiment. And if it's not, that's a huge red flag. So they have to share how they got their data, how they set up the experiment or even just the data gathering if it is a meta-analysis. They didn't necessarily run the experiment. But how do they find it and then how did they analyze it?

Exactly. Exactly. I'll spend a couple of minutes just on how they did that, because this is so important when you're looking at a meta-analysis. Now, the number one thing to highlight, of course, is that they have what's called "predefined exclusion criteria."

Okay.

That means before they ever did any search in PubMed and Scopus and all of these other places they looked, before they ever searched anything, they came up with criteria that's going to exclude [some] studies that they're going to find. Because they know they're going to find a whole smorgasbord. So, how do they know which ones to put in a meta-analysis? And of course, you need studies that are going to be somewhat similar in their methodology. So it actually makes sense to pool the data together in the first place. Okay, so I'll go through a couple, not all of them. Of course, they're looking for studies that are in English. They're excluding studies that are textbooks and book chapters, review chapters. So, things that were not an actual study itself.

What they are looking for is the primary research articles.

Primary research. Yes.

Gotcha.

On people. So, that's another criteria, they're looking at food cravings in people. They also excluded anything that was not an interventional study.

Oh. . .

What this means is they are excluding observational studies. They're looking for studies where people literally changed their diet. They went on a calorie-restricted diet for at least 12 weeks, and their food cravings were measured with a standard questionnaire before they started their diet and [again] afterward. They also excluded, for example, people who are diagnosed with eating disorders. And we can guess why. The first thing that came to my head is that people who experience eating disorders may have a different level of cravings that they experience differently from other people. So they, in fact, might need their own study.

Well, I think, too, because there's more of a mental health issue around eating disorders. There are a lot of other psychological influences going on. That's kind of where I went with that.

Right. Yeah. So, they weren't part of this particular study. But I do strongly believe that there should be, and there probably are, studies just for that particular group.

Yeah.

They also looked for any study that was more than 12 weeks long because they want to really get the sense as to whether calorie restriction changes your food cravings and not just a day or two of restricting, but minimum three months, 12 weeks. Long term. So they did some super fancy statistical analysis using the R software.

Okay.

And what they measured was these questionnaires from before and after, on these different types of cravings that we mentioned; for overall food, and then sweet food, high fat, fast food, and even fruits and vegetables, which is hilarious. And I'll tell you that in a second. Okay, so here's the overall results. Cravings reduced! So, out of a score of five, cravings for overall food were 0.25 points (a quarter of a point) less after the 12+ weeks of calorie restriction versus before.

Yeah.

Sweets had the highest decrease! The cravings went down the most for sweets. And that was 0.41 points. So, not quite half of a point out of the full 5-point scale.

Okay, so here's where it starts making sense, because if you were on a calorie-restricted diet, there's a lot of high-fat food and there's a lot of high-sugar food. Those are all the calorie-dense foods. As soon as you start taking those away, you start balancing blood sugar. And so your body isn't in this seesaw now, with this fight between high blood sugar/low blood sugar, high insulin/low insulin, all of these different things. So, it makes sense that you're not getting that positive feedback loop anymore. And so you're craving for sugar will be reduced.

That could very well be part of it as well, because the whole structure of this study was when people are literally restricting their nutrients. They're restricting their energy intake, they're lowering their calories. And they've spent 12 weeks conditioning themselves to get used to eating fewer calories. What does this do with the cravings? And again, if this goes to how much is physical need (the deficiency model) versus how much is the psychological conditioning model? There are so many interconnections that could be playing out here. So, we have a reduction in [cravings for] overall food of 0.25 points, reduction in sweet food 0.41 points. Sweet food cravings reduce the most. And then, as you mentioned, high-fat food. High-fat food reduced by 0.19 [points] and fast food by 0.29 [points].

Oh, that's fantastic.

What this overall showed for these top cravings was on a scale of one to five, after 12 weeks of calorie restriction in people who have obesity, sweet food cravings reduced the most, at not quite half of one out of five [0.41/5]. And the rest of them reduced in and around a quarter of a point out of five [~0.25/5].

This is really interesting because it makes sense. I mean, the less you eat it, the less you're going to crave it because your body becomes reconditioned, both physically and psychologically. So it really is a positive feedback loop. The more junk food you eat, the more you crave it, the less junk food you eat over time, the less your body craves it. It's just a matter of getting over that hump of craving it and just willpower fighting through, which is hard. I'm not going to lie. And that's hard. I mean, advertisers work damn hard to make sure that you don't forget about them. But you can do it if you can get past that hump and just give yourself a goal of a month, it's going to be easier on the other side and those cravings are really going to diminish over time. That's so cool.

Right. So, these cravings diminished by a small amount after 12 weeks and it puts a bit more weight on the conditioning theory [model] versus the deficiency theory that you can train your body, and eventually the cravings will start to peter out versus your lacking food and your cravings go up. Now, of course, people are going to experience all different kinds of things and they're going to be people who their cravings increase and not. But what the study looked at was multiple different studies and multiple different people that overall, on average, cravings decreased slightly on the other side of twelve weeks, which is positive because, as you said, dieting is hard.

Yeah, it's really hard. Okay, fruits and vegetables--my favourite topic.

Fruits and vegetables made me laugh because we don't talk about fruits and vegetables cravings and this is kinda why. . . . Fruits and vegetables are part of the cravings questionnaire they asked. And I have to read the quote from how the researchers describe this. They wrote, "cravings for fruits and vegetables did not significantly differ from zero in the meta-analysis conducted." So #PoorFruitsAndVegetables, pretty much zero. People don't generally crave them. And this is just a reality that we all kinda knew. But, yeah.

Which is okay. For the scientific experiment of one on myself, I know if I go for too long without eating enough vegetables, I definitely start to crave them. But, I mean again, I'm just a study of one. If I've gone for too long, if [there are] lapses or if life gets really busy, which happens with three kids and a lot of other things going on. So If I'm eating badly, then after a few days I'm like, "I feel gross. I need my big salad."

Right, and the food craving is that like intense desire for this particular food, like right now.

Yeah, I guess overall maybe I'm an oddity. I'm the odd one out.

But the thing too is this study was done on a particular population. I mean, we could do this study on any population.

Yeah.

And see how it is. And see--I'm now curious--in how many people do cravings for fruits and vegetables significantly differ from zero.

And also, I mean, I've been eating this way--a healthier way--for quite a while now. And so, I mean, this is going on for obviously more than three months. We're talking years and years.

You've been conditioning yourself.

I have been conditioning myself. I mean, one of the things I had to do is change my relationship with food. And that's definitely had a huge effect on what I eat. I don't know about you, but . . . Do you ever crave vegetables?

Ummmm.

[Laugher] You're with the majority.

I eat them. I like them. But when it comes to like, "OMG, I need to eat something right now," they're not top of my list.

Yeah.

But, it's okay.

I don't think they're ever on the top of anybody's list, ever. But there are definitely days where it's like, "OMG, I'm really craving Brussels sprouts with my steak with dinner," or something like that.

That's amazing.

I think we're establishing I'm a bit different. Okay, go on.

That's what's called an "outlier."

Yes, I am an outlier.

In scientific research, an outlier, right.

Yeah.

Okay, so just to close out on where the stands is, what this study established is that in general, people with obesity, who've been on a 12 week calorie-restricted diet (or longer) do tend to have smaller cravings for the typically craved foods (sweet, high-fat, starchy, and fast foods) that are smaller after at least 12 weeks of being on a calorie-restricted diet. So, do our bodies crave things because we're deficient in them? Maybe. Maybe, to a certain extent.

Yeah.

The conditioning, the getting used to something, getting used to not eating those kinds of foods might actually have a bigger role to play in cravings, rather than deficiencies.

So just to play devil's advocate here, I totally agree with what you're saying, but I'm wondering if the deficiency play doesn't come in. Because if you're cutting back on "bad foods," (I don't really like that saying) the comfort foods that we're talking about. You have to fill your stomach with something. And so the best way to fill your stomach without getting all the calories is by eating more vegetables and eating more of these "clean foods" that tend to be more nutrient-dense. And so just by default, you are probably getting more of these micronutrients that your body needs. And so I'm wondering if these two different theories [model] are kind of playing off each other. Where you're getting a decrease in cravings because you're not eating them anymore. So your taste buds change and what your body wants changes over time. But at the same time, now you're nourishing your body a little bit better because you're not filling up on junk food. 

And we can look back to see what type of calorie restrictions that they had. Because that is possible that their calorie restrictions were to start every meal with a fruit or vegetable. I didn't go to that level of detail versus having a nutrition shake.

Yeah.

I didn't go into that level of detail. But that is another good point is with nutrition, and part of what makes nutrition research difficult, is that you generally replace food with another food.

Yes. Because you still have to fill your stomach somehow to get that feeling of satiety, otherwise it's not going to last long, you're eventually going to hit the breaking point where you're just so hungry you'll eat your own arm.

And diets are so hard. They're so hard.

You have to eat. But it's just what you eat, what is on your plate is really what makes all the difference.

And how much. What and how much.

Yeah.

So a couple of last thoughts on the study was that this was not an observational study. This was a pooling of interventional studies, which makes it a pretty good study to look at when they did the meta-analysis. And that it was sponsored by the National Institutes of Health. So this is, again, a highly respected place through the United States government where it's not a commercial interest per se.

I was going to say we're reducing potential bias there.

Reducing commercial bias, yes.

There's not to say there's no bias, but we're eliminating one of the potential sources of bias.

Exactly.

Yes.

And also the researchers were from different countries. So they were in the United States and Sri Lanka. Which is always nice that there are collaborations between different researchers in different countries and different institutions because it gives different perspectives on it. And with people working together internationally, the results are interesting, I think, a little more than if it's one person in one institution. Those were positive strengthening factors in my mind. So that, in a nutshell, is this study that is linked to below. So people with obesity who'd gone on at least a 12 week diet.

Yeah.

Do have reduced cravings for pretty much all the standard cravings, and there may still be some nutrition deficiency in there, but this shows that the conditioning response is probably a little stronger in most people. And that is great to know if you are on a diet or if you are helping people through calorie-restricted diets. They're so difficult and this maybe a little bit of light at the end of the tunnel.

There is a light at the end of the tunnel. You know the craving isn't going to last. You know there's going to be an end. And all you have to do is fight through. The other thing that I found that I've heard a lot of other people agree with--again this is just my own personal experience in the field. . . I have a sweet tooth. I love sugar. And it tends to be all or nothing. I am not one of those people that can just eat a little bit of a treat. And so I find for me--because I don't want to be eating that stuff--it's easier just to avoid it altogether. Because again, if I have a little bit, I have a lot. And so, knowing that the craving will get easier the longer I go without it is a good thought to keep with it as I am trying to improve. Because, this is a journey, right, you're always to modify your diet and improve and you have fallbacks and you have stressful moments and you have celebrations which tend to foil all your intentions.

But yeah, it's good knowing that it will improve over time. So this is a good study.

Yes, thank you.

Good article, good choice.

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Thanks, guys.

Thank you so much. And we'll see you in a couple of weeks with another exciting episode.

Yes.

I can't wait.

Awesome. Thanks.

Thank you for listening for exploration into more health research, don't forget to subscribe. And we'd like to thank Joseph McDade for the music. If you have any comments, ideas, or recipes to share, you can reach us at rEATsearch on Instagram and Twitter and rEATsearch podcast on Facebook. That's spelled r-E-A-T-search.