How Gut Bacteria Can Help You Eliminate Junk Food Cravings

cupcakesDo you regularly get cravings for doughnuts, pizza, ice cream, or other unhealthy foods high in sugar and fat? You’re not alone. Over the last couple of decades, obesity rates have steadily climbed all over the world and fast food joints have made their way onto every street corner. We’re surrounded by evolutionarily novel temptations, one of which being hyper-palatable food that bear little, if any, resemblance to the types of foods our Paleolithic ancestors consumed.

However, the fact that chocolate, doughnuts, and pizza are now cheap and easily accessible doesn’t mean that we have to eat them. We do have the option of shopping the outer aisles at the supermarket, which is where the fruits, veggies, and lean meats tend to be located, instead of venturing into the inner aisles to get a hold of salty, sugary, and fatty foods that come in a box or can. After all, we all know that these types of foods aren’t good for us and that eating them, at least on a daily basis, can wreak havoc on our health and lead to a rapidly expanding waistline.

So, why do so many of us find it difficult, if not almost impossible, to avoid eating burgers, fries, chocolate bars, and other processed foods? Can we blame it all on a lack of discipline and self-control? 

No, we can’t… Here’s what one of my favorite research papers had to say about the matter:

Conventional wisdom often blames unhealthy eating on a lack of willpower. However, binge eating is not just a matter of mental control [101]; food cravings are unlike other cravings. Many other addictions, such as drugs and alcohol, require ever-increasing doses to maintain the same mood-altering effect. This habituation does not happen with food. For some individuals, the more they indulge their food cravings, the more enjoyment they get from them [102]. These results, and recent work showing distinct mechanisms of food-reward and morphine sensitization in mice suggest that overeating has a different underlying mechanism from drug abuse, and is not consistent with an addiction [103]. (1)

Cravings for calorie-dense, highly palatable foods can’t solely be explained by the fact that once-adaptive physiologic mechanisms regulating energy intake and eating behaviour are mismatched to modern environments

In a recent article I made the case that one of the main underlying reasons we now have an obesity epidemic is that we humans have an innate, evolved appetite/preference for foods that are calorie-dense and rich in fat, sugar, and/or starch.

When hunter-gatherers leave their camp and head on out into their local environment in the search for food, their aim isn’t to bring back low-calorie vegetables, but rather to get a hold of meat, honey, and other foods with a relatively high energy density. That’s not to say that they won’t eat anything they can get their hands on if they’re hungry and food is scarce, but as a general rule, they’ll try to get a hold of foodstuffs that provide them with ample amounts of calories.

We naturally seek out behaviours that increase our chances of survival and reproduction, and avoid those that undermine our ability to pass on our genes. The problem is that many of the evolved adaptations that helped our ancient ancestors thrive in the niche they had carved out for themselves on the African savanna are working against us in today’s world of abundance.

As for food, having a strong appetite for calorie-dense foods obviously didn’t make our primal ancestors fat, because back then, meat and honey were the most energy dense foods around and food procurement often involved hours of walking, running, and carrying. However, as we know, the situation is now very different.

So, you can see, from an evolutionary perspective it makes complete sense that so many of us seem to find it almost impossible to stick to a diet and avoid highly palatable and energy-dense foods. However, this certainly can’t be the whole story. It can’t explain why some people experience strong cravings for doughnuts and candy every afternoon, while others seem to have no problem sticking to a healthy diet and rarely feel the desire to eat something very sweet. Also, it can’t explain several other phenomenons, such as why some people get “addicted” to evolutionarily novel foods like chocolate, or why a lot of people report that their cravings for nutrient-poor, westernized foods become much less pronounced if they make a conscious decision to only eat healthy whole foods (e.g., the Paleo Diet) for some time.

How gut bacteria exert control over your appetite and eating behaviour

A couple of years ago I started writing about the role gut bacteria play in shaping our food preferences and appetite. At the time, very little research on this topic was available, but several indirect pieces of evidence had made me believe that our food preferences and appetite are partly (largely?) controlled by the gut microbiota. In the years that have passed since then, more and more research has come out that support this theory (e.g., 1, 2, 3, 4), and I’m now completely convinced that the bacteria in our gut can exert control over our appetite and eating behaviour.

There are several potential pathways bacteria in our gut can use to influence our behaviour. Among other things, they produce neurotransmitters and hormones that travel from the gut to the brain and they regulate the inflammatory tone in our body.

I’ve previously discussed the research in this area, so I’m not going to do that again here. However, to set the stage for the rest of the article and to get you on board with the idea that our food preferences are partly shaped by our gut bacteria (which probably does sound a bit “out there” if you’re new to this idea), I thought it best to include another quote from the scientific article I brought up earlier.

Modern biology suggests that our bodies are composed of a diversity of organisms competing for nutritional resources. Evolutionary conflict between the host and microbiota may lead to cravings and cognitive conflict with regard to food choice. Exerting self-control over eating choices may be partly a matter of suppressing microbial signals that originate in the gut. Acquired tastes may be due to the acquisition of microbes that benefit from those foods. Our review suggests that one way to change eating behavior is by intervening in our microbiota. (1)

Are sugar-loving microbes ruining your weight loss efforts?

As those who’ve been following the research on the microbiome know, the gut microbiota can rapidly respond to changes in diet. E.g., a fiber-rich ancestral diet will select for a very different gut microbiota than a sugar-rich, Western style diet. However, what is less known is that (as mentioned) our gut bugs play a role in shaping our eating behaviour.

I believe one of the main reasons so many people have trouble losing weight – and keeping it off – is that they harbour a proinflammatory microbiota that’s not only wreaking havoc on their metabolic health, but that’s also driving them to make unhealthy food choices.

Let me do an example to illustrate how this may go:

Joe, 27, has been overweight for most of his life. He’s tried numerous supplements and diets over the years in an attempt to lose the annoying and aesthetically unappealing body fat that has accumulated around his hips and abdomen, but without success. Besides carrying more fat mass than he’d prefer, he’s also been experiencing some other health issues, including fatigue, poor sleep, and low libido. When compared to the average westerner, his health condition isn’t particularly bad, but it could definitely be better.

As a child, Joe ate what a lot of kids seem to eat these days, namely cereal and skim milk for breakfast and a sandwich, chocolate bar, and soda for lunch. For dinner, his mother – who has also been struggling with her weight for most of her life – either served a homemade meal or bought something in a fast food joint on her way home from work. At home, there was usually some candy lying around, which Joe regularly consumed after school or late at night. Like most kids growing up in Western nations, Joe was often sick and took several courses of antibiotics during his childhood years.

Joe’s main problem is that he finds it almost impossible to stay away from potato chips and high-fat cream and that he always get cravings for sugar late at night. When he’s tried counting calories in an attempt to lose weight, he just seems to get hungry and fatigued, and after a couple of days – or sometimes a week or two – his cravings typically get the better of him.

After years of failed dieting he has succumbed to the idea that he’s destined to stay fat and that his sugar cravings will stay with him for life. He hasn’t completely given up hope though. He regularly tries new diets and supplements aimed at boosting fat loss, but his attempts have become more and more feeble.

So, what’s going on here? Why does Joe find it so hard to eliminate junk food from his diet and achieve sustained weight loss? I believe – and the science suggests – that his gut bacteria are partly (largely?) to blame for his cravings. Joe undoubtedly has a damaged gut microbiota, something that has impaired his leptin and insulin sensitivity and contributed to making him chronically inflamed.

His diet, in combination with antibiotic use and other microbiota-upsetting stimuli, has caused an overgrowth of proinflammatory bacteria in his upper GI tract, as well as a degradation of the colonic microbiota. His diet selects for a specific microbiota; and the microbiota impacts his brain in such a way that he craves more nutrient-poor, sugar-rich foods. He’s caught in a vicious cycle. The solution: Diet changes and manipulation of the gut microbiota.

The new research in this field changes everything

The new and emerging research in this area is opening up entire new avenues and possibilities, such as:

  • Our collective desire for junk food may partly be explained by the fact that there’s now an epidemic of damaged gut microbiota in westernized societies. For decades we’ve been bombarding our gut microbiomes with broad-spectrum antibiotics and processed foods. We’ve also distanced ourselves from the microbe-rich natural environment in which we evolved and partly replaced natural births with c-sections and breast milk with infant formula.
  • We may be able to develop probiotic supplements and microbiome modulators that change our food preferences and eating behaviour.
  • Food preferences may be contagious.

As for the last statement, the authors of the excellent paper I’ve discussed throughout this article had the following to say:

One intriguing implication of microbially induced cravings is that preferences for certain foods may be contagious [97]. Both the fecal and oral microbiota are more similar among cohabiting family members compared to non-cohabiting individuals [98]. If the food preferences of one person in a household influence the food consumption of the household, any specialist gut microbes adapted to that diet would then tend to flourish in the other household members. Even worse, the obesity epidemic could be contagious as a result of obesity-causing microbes transmitted from person to person. A social network study of 12,067 people found that a person’s chance of becoming obese increased by 57% if a friend had become obese [99]. This raises up the possibility that cravings and associated obesity might not be socially contagious (e.g. through changes in norms) as the authors of the social network study suggest [99], but rather truly infectious, like a cold [75]. (1)

Practical takeaways

If you regularly experience cravings for cheese, pizza, chocolate, or other similar calorie-dense, highly palatable foods, you should consider giving a strict Paleo Diet a 15-30 day try. Remove all of your favorite convenience foods from your diet during this time period. For some, this is enough to largely eliminate cravings for sugar and junk food, as the gut microbiome will adapt over time to the diet you’re eating.

However, others may find that diet changes aren’t enough to curb their undesirable food cravings. Oftentimes, the problem is that their gut biome is mismatched with their diet, and hence, they also have to implement additional steps – such as consuming beneficial bacteria, getting out of a toxic environment, or increasing their intake of prebiotics – to nudge their gut microbiota in a healthy direction.

All of this is not to say that the gut microbiota is the only player involved in all of this. Also, I’m not saying that if you fix your diet and gut microbiota, you’ll never crave chocolate ever again. However, there’s little doubt that the critters deep in our gut exert a strong influence over our brains…

Picture: Creative Commons picture by Frédéric BISSON. Some rights reserved.

Comments

  1. Eirik, I think you’re giving short shrift to the mental/emotional aspect, which can be a pretty powerful thing, and that it really is a case of mind over matter.

    I know from personal experience that switching to a Paleo diet and eliminating sweets and most grains does eliminate the cravings after a week or so. (This probably varies from person to person.) However, it can take considerable willpower to get through that first week, until the cravings disappear. In fact, for many people who grew up on a junk food diet and actively prefer to eat that way, it takes considerable willpower just to embark on a strict Paleo-type diet, much less remain on it long enough for the cravings to disappear. If you hate what you are forcing yourself to eat (meat, fruit, vegetables) and would really rather have something you consider more palatable (pizza, pasta, sweets, etc.), the mental cravings might never go away.

    I have no doubt that gut bacteria plays a major role in our overall health, but to say that the gut microbes control our thought processes and our desire and ability to do something about our weight problem seems a bit of a stretch.

    • I agree with everything you’re saying. The mental and emotional aspect is important, and I think no one would disagree that a lot of people find that “it takes considerable willpower just to embark on a strict Paleo-type diet, much less remain on it long enough for the cravings to disappear”.

      However, this post was about the control bacteria exert over our appetite and food preferences. I didn’t get into every factor that play a role in all of this. Inadequate sleep, stress, and depressive feelings are some of the many other things that can promote unhealthy food choices. As I mentioned in the end, I’m not suggesting that gut bacteria are the only players involved here.

      I appreciate your regular feedback and comments! Keep them coming.

      • Hmm… Okay, thanks for clarifying. I was getting the distinct impression from the article (which I admit I only skimmed) that gut bacteria is now considered the culprit in unhealthy food cravings–which I don’t agree with. Certainly the gut microbiata plays a role, particularly as pertains to wellness versus disease, but I don’t see it as being thought-controlling.

        Historically, research regarding what makes us tick often lacks a sufficiently accurate data base and is therefore satisfied with assumptions and superficial conclusions without recognizing a need to delve deeper. If this were not the case, we would not have so many instances of yesterday’s cutting-edge science becoming today’s debunked theories. In other words, most research should probably be taken with a grain of salt until the test of time proves it to be gospel.

  2. Eirik, thank you for this thought provoking post. I think you are right on.
    Here’s a link to an article that says – “study in humans has shown that the transformation of the gut microbiome can occur by dietary effect within 1 day.[2] It has therefore become a prominent question how much of a role bacterial flora play in systemic diseases, rather than simply in the day-to-day processing of the food groups that we eat.”
    http://www.medscape.com/viewarticle/850764?src=wnl_edit_specol&uac=199037AZ&impID=829265&faf=1

    • Yes, as you mention, the microbiome rapidly responds to changes in diet.

      Rather than saying that “we are what we eat”, it may be more accurate to say that “we are what our microbes eat”.

Trackbacks

  1. […] The bacteria in your gut play a key role in controlling your hormone levels, appetite, and food preferences. While a healthy community of gut bacteria will help you maintain a lean, well-functioning body, a dysbiotic gut microbiota can make you metabolically deranged and “addicted” to sugar. […]

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