Can Fiber Make You Happy?

fresh-vegetablesIf you ask one of your friends what his current goals in life are, he may list a whole host of things, such as getting a better paid job, losing 10 pounds, and making junior partner at work. If you continue by asking why he’s setting these types of goals for himself, he may reply that it’s because he thinks he will be happier and have a better life when he achieves his objectives.

Because that’s the ultimate goal, isn’t it, to be happy and satisfied with life?

If you watch the Dr. Phil show or read about “positive thinking” in a health and wellness magazine, you may get the impression that overcoming depression and achieving happiness is all about making a conscious decision to change how you think and look at the world. Basically, you have to change how you feel by changing how you think.

Is that really what it’s all about – or is there something deeper going on? Could diet quality, fiber intake, gut health, and microorganisms, which are something most people look at as completely unrelated to depression and mood, actually be key things to take into account in the quest for happiness?

Fiber intake has plummeted since the Paleolithic era

Our primal ancestors ate a lot of fiber when compared to the average Joe and Jane of the 21st century. Not because we humans are naturally drawn towards fiber-rich foods (the popularity of low-fiber, Western-style diets clearly shows that we aren’t), but because most of the foods that are available to hunter-gatherers (both ancient and contemporary) are naturally high in fiber.

Uncultivated fruits and vegetables tend to be markedly higher in fiber than the domesticated versions you find at the grocery store down the street, and as for meat, Paleo man (and woman) didn’t have the luxury of only eating the most tender and juicy cuts of the animals they tracked down. Rather, they probably also consumed gristle, tendons, and other chewy, fibrous parts of the animal, at least when food was scarce.

Hunter-gatherers consume a less calorically dense diet than most of us do today, as they haven’t got grass-fed butter to put on their steak and don’t consume sugar-filled beverages and other calorie-dense foods that many contemporary humans eat on a daily basis. Hence, they have to eat a greater total volume of food to acquire the same amount of calories as a doughnut-eating office worker.

Combine all of this with the fact that our primal forebears didn’t have access to all the devices and tools we now use to cut, blend, mash, juice, refine, and process our food, and you can quickly understand why studies suggest that the intake of dietary fiber has plummeted since our hunter-gatherer days.

As the knowledgeable reader will point out, there are some hunter-gatherer populations (e.g., the Inuit) who didn’t eat a very fibrous diet. However, these cultures are the exception rather than the norm, and their diet is not a good representation of the type of diet that conditioned the human genome.

Estimates suggest that most hunter-gatherers consume at least 70 grams of fiber/day (1), which is what the average Joe eating a Western-style diet may consume in 3-5 days. Again, not because hunter-gatherers prefer to eat fiber-rich, low-calorie vegetables over a fatty cut of meat, but because most of the foods that are available “in the wild” are fairly high in fiber.

All in all, I think it’s safe to say that humans evolved to eat a fiber-rich diet.

Every time we deviate from the Paleolithic baseline, bad things tend to happen. For some dietary components, such as sugar, salt, starch, and the rest of the nutrients that are combined to make chocolate, doughnuts, and other Westernized foods, the problem is that we now eat too much. For other nutrients, such as omega-3 and fiber, the problem is that we eat too little. The end result is the same, our health suffers.

Even those people who have never paid much attention to nutrition or healthy eating usually know that consuming fiber-rich foods is important for a healthy digestion. Those with a little more knowledge about the topic will typically tell you that it’s primarily resistant starches, inulin-type fructans, and other fermentable fibers we should make sure we’re eating enough of, as these compounds can help promote a healthy, diverse gut microbiota.

Okay, so eating “enough” fiber is obviously important to achieve good health, but how does all of this tie in with happiness, depression, etc.? Let’s investigate…

Mind-altering microbes

As the research on the human microbiome has progressed, which it has at a rapid pace these last couple of years, it has become increasingly clear that mental health problems such as depression, ADHD, and autism may not “start in the head” after all, but rather in the gut. Recent research has made it abundantly clear that gut bacteria have a potent impact on our thoughts, behaviour, and feelings, which essentially means that “we” (the human hosts) are not in complete control of how we act, what we eat, and how we feel.

It may seem like a scary thought that microbes in your gut can control your mind. However, on the other hand, it’s also an empowering thought in the sense that we now understand that we have the ability to manipulate our feelings and mental health to an extent never previously thought possible. By sculpting and tweaking the microbial ecosystem in our gut – perhaps through diet changes or the use of probiotics and prebiotics – we may be able to change how we feel and think.

What does the scientific research say?

To get you on board with the idea that the critters lurking deep in your gut can have a major impact on your mood, I thought it best to start with some quotes from some recent research papers in this area. If you are already convinced that a well-functioning gut is critical to a healthy mind, you can skip this part.

  • “We now know that depression is associated with a chronic, low-grade inflammatory response and activation of cell-mediated immunity, as well as activation of the compensatory anti-inflammatory reflex system.” (2)
  • “Studies in germ-free animals and in animals exposed to pathogenic bacterial infections, probiotic bacteria or antibiotic drugs suggest a role for the gut microbiota in the regulation of anxiety, mood, cognition and pain” (3)
  • “Recent studies published in this Journal and elsewhere demonstrate that there is a distinct perturbation of the composition of gut microbiota in animal models of depression and chronic stress. This has direct implications for the development of psychobiotic-based therapeutic strategies for psychiatric disorders. Moreover, given that affective co-morbidities, such as major depression and anxiety states, are common in patients presenting with irritable bowel syndrome (IBS), it may have implications for functional bowel disorders also.” (4)
  • “Although in its early stages, the emerging field of research focused on the human microbiome suggests an important role for the gut microbiota in influencing brain development, behaviour and mood in humans.” (5)
  • “Emerging studies show that the normally very selective intestinal barrier may be compromised in depression (and in numerous conditions where depression is often a hallmark symptom).” (6)
  • Patients with major depressive disorder have an altered fecal microbiota composition (7).

Depression is an inflammatory disorder

As mentioned above, there is now solid data to show that depression is an inflammatory disorder, which means that depressed people have higher levels of circulating inflammatory markers in their blood. Many theories have been proposed as to where this inflammation stems from, with a common denominator being that the gut plays a critical role.

I’ve previously talked a lot about the connection between diet, gut bacteria, and chronic inflammation, so I won’t delve into that here, other than to say that a high-quality diet and a healthy gut microbiota may be your best defense against chronic low-grade inflammation.

There are a whole host of factors associated with a modern diet and lifestyle that can cause chronic low-grade inflammation. The environment we live in today is markedly different from those we evolved in for millions of years, and the diet and lifestyle most of us adhere to have few similarities with that of our primal ancestors’. Natural selection has been outrun: our bodies are attuned to an environment that is long gone. One of the biggest problems is that most of us eat a diet that is poorly matched with our ancient genetic blueprint.

As you know if you’ve been reading this blog for some time, I believe singling out just one or two dietary components as the evil culprits behind the obesity epidemic (“carbs make you fat!”) or the high prevalence of cardiovascular disease in industrialized societies is a mistake. We have to look at the whole diet, not just a couple of nutrients. However, I think certain components of our diet do deserve some special attention, one of which being fiber.

Could the low-fiber, sugar-rich modern diet be partly to blame for the high prevalence of depressive disorders in contemporary societies? I think so.

Most of the nutrients you get through a Western-style diet are digested and absorbed in the small intestine, leaving little for the critters deep in the colon. This may initiate a vicious circle of events, as shown in the illustration below.

When the microbiome is degraded, pathogenic microbes are more likely to get a foothold, which may explain why depressed could be more susceptible to pathogenic infections than non-depressed people. Some researchers have even proposed that depression could be caused by a microbial infection (8).

A vicious circle


The illustration above shows how consumption of a processed, low-fiber diet may lead to depression. The diet-gut microbiota-depression connection is a vicious circle, because we know that gut bacteria have the ability to impact our dietary preferences and that depression can lead to increased consumption of “unhealthy” foods.

Keep in mind, there’s still a lot we don’t know about the microbiome-gut-brain axis and we’re constantly learning about new ways bacteria can communicate with our brain. In other words, our understanding of the connection between diet and depression will undoubtedly change over the coming years.

Final words

By fixing your diet and gut microbiota you’ll not only achieve better health, but you may also become happier and more content with life. An adequate intake of dietary fiber is especially important when it comes to achieving a diverse, healthy gut microbiota. However, keep in mind that sugar intake, pharmaceutical use, microbial exposure, food quality, and all of the other things I regularly talk about on this site also play a key role. Last but not least, remember, it’s not enough to just eat a lot of fiber-rich fruits and vegetables, you also need a gut microbiome that is adapted to break down the indigestible (to the human host) compounds you get from these foods.

The next time you see a depressed friend or family member of yours sipping coke and eating doughnuts, you could do him a favor by telling him that his diet may be making him unhappy – and that he should consider eating more greens and less sugar.

What are your thoughts on all of this? How much of an impact do you think the microbes in your gut have on your mood?

Picture: Creative Commons picture by Rich Ligthelm. Some rights reserved.


  1. Great summary post about the gut-brain axis, I hope people pass this on to those who do not currently follow your blog!

  2. Eirik, you (and others) keep referring to the unhealthiness of a “Western-style” diet. I think it’s important to differentiate between that and a grain-heavy junk food diet. A Western diet can be a Paleo diet or a donut diet. They aren’t necessarily one and the same, even though they are both Western in content and origin. There are Eastern-style diets that I wouldn’t consider very healthful; i.e. rice-heavy with minimal protein and veggies. My point is that locale is often unrelated and therefore meaningless as a description.

    • Shary, I understand your confusion.

      In the scientific literature, terms such as the “Western diet” and “Western pattern diet” are used to refer to a diet that is characterized by high intakes of refined sugar, refined fat, salt, saturated fat, and omega-6. In other words, a nutrient-poor, highly processed diet.

      “The Standard American Diet” is also commonly used to describe a diet with these characteristics, but I prefer to use the term “Western dietary pattern” or “Western diet”, as the diet described above is popular in developed, “westernized” nations all over the world, not just in America.

      I’m perfectly aware that not everyone in Western societies eat this type of diet.

      You can read more here:

  3. Quite honestly I believe this article is mostly right, however I also believe that *sometimes* it’s more like “which came first, the chicken or the egg” meaning that sometimes it just really is the brain that wreaks havoc on digestion and not the other way around.

Do you have any comments or questions pertaining to the article? If so, please feel free to post them below. Note: Comment moderation is in effect. Spam, rants, hateful remarks, etc. will be deleted.


Get every new post delivered to your Inbox

Join other followers: