We’ve been told to “eat our greens” for so long when we were kids that growing up has become the moment when we can just eat anything we like and not give anyone any account of it. Unfortunately science has sided with the wisdom of the past and “eating our greens” has become a way of maintaining longevity as well as physical and mental health.
Luckily for us who might retain a little bit of the childhood trauma to being told what to eat and have an aversion to “eating greens” it’s more about increasing the fiber in our diet (also known as roughage) than just simply eating green things we may not quite know how to cook.
Fiber is a dietary component that we cannot digest. It appears therefore to be of little direct nutritional value to us. That doesn’t mean it is not useful. Generally speaking, dietary fiber is the edible parts of plants, or similar carbohydrates, that are resistant to digestion and absorption in the small intestine. It usually comes in two types: Soluble Fiber that can be dissolved in water (it is usually found in oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium) and Insoluble Fiber that passes through the digestive system relatively unchanged (typically found in whole-wheat flour, wheat bran, nuts, beans and vegetables, such as cauliflower, green beans and potatoes).
Why Is Dietary Fiber So Important?
Although we can’t directly digest fiber scientific evidence suggests that the millions of bacteria that live in our microbiome can. The logic of how eating more fiber (a thing we can’t digest) benefits our health directly goes like this: Our body needs a host of nutrients and enzymes which we cannot directly manufacture. These nutrients and enzymes are created by the bacterial colonies in our microbiome. These bacteria secrete enzymes that help them break down the dietary fiber as it moves through our body and digest it. It helps increase their population which then leads to increases of specific nutrients and enzymes those bacterial populations produce. Those secretions affect us at a cellular level and lead to a longer lifespan, fewer life threatening-diseases and better mental health. 
A study carried out by researchers at Georgia State University fed mice a diet that was, on purpose, low in fiber and high in fat  (which is the equivalent of a human junk-food diet). Those mice populations crashed as mice died from old age related illnesses sooner than expected and younger mice developed physical and mental illnesses.
What they discovered was that the mice that were fed this diet developed shorter bowels with a thinner intestinal wall. This allowed bacteria to get much closer to the blood stream triggering the immune system and developing chronic inflammations, started to get fat and suffered from higher blood sugar levels.
What is more important here is that a lot of this damage was reversed when more roughage a.k.a. dietary fiber was introduced into their diet. What was more dramatic however was that the control group of mice that had a high-fiber diet to begin with gained less weight, aged slower and was generally much healthier even when other aspects of the diet were not so ‘healthy’ – i.e. it contained a higher percentage of fat or sugar than average. The reason for this was because their gut bacteria had plenty of dietary fiber to fuel them. The intestinal walls therefore were thicker, the intestinal tract longer and the immune system healthier.
A healthy immune system protects us from disease. All disease, both internal and external. It keeps us from getting run down by colds and other external pathogenic infections [3, 4] and it reduces the risks of inflammation in our arteries that can lead to strokes and heart attacks. [5, 6]
The old adage of “an apple a day keeps the doctor away” is actually pretty good advice. Apples are rich in soluble fiber  and soluble fiber helps strengthen the immune system better than insoluble fiber. This is not to say that insoluble fiber is any less important. Quite the opposite in fact as it plays a role in regulating weight, maintain blood sugar levels, regulating the appetite and the body’s metabolism. [8, 9]
How Much Fiber Should We Eat?
The current guidelines from The British Nutrition Foundation, a registered charity organization that provides impartial, evidence-based information on food and nutrition, suggest we need to ingest 30g of fiber each day to stay healthy. Their studies indicate that in the U.K. the average daily intake of fiber is 18g. The advice is mirrored by the American Heart Association whose own studies indicate the average intake of fiber in the U.S. is 16g per day.
The Health Benefits of Eating Enough Fiber
The numerous health benefits of eating 30g of fiber each day are:
- Normalized bowel movements.
- Better bowel health.
- Lower cholesterol levels.
- Lower blood pressure.
- Less inflammation.
- A stronger immune system.
- Lower blood sugar levels.
- A healthier weight.
- A longer life span .
- Better brain health.
- Smaller risk of a heart attack.
- Smaller risk of strokes.
- Smaller risk of diabetes 2.
- Healthier bones.
- Smaller risk of some cancers.
- Reduced Blood Glucose Levels .
- Increased Insulin Sensitivity.
- Increased Mineral Absorption.
Food Sources Rich In Fiber
In order to get more fiber on a daily basis it isn’t necessary just “eat your greens”. The easiest way to significantly increase your daily fiber intake is to switch to:
- Whole grain bread
- Brown rice
- Whole wheat pasta.
Instead of using white potatoes, switch to their “sweet” counterpart. Just this alone will double your fiber intake.
If you like your pasta as it is, your potatoes non-sweet and your bread white, start adding other items:
- Add a handful of nuts and seeds to one of your meals daily
- Eat at least one fruit a day
- Add a cup’s worth of beans, chickpeas, lentils and/or peas to any meal
- Eat oats for breakfast every other day
- Eat a colorful salad at dinner
- Occasionally, treat yourself to air-popped popcorn or dark chocolate - both are surprising rich in fiber!
Other foods rich in fiber you can incorporate to your daily diet are:
- Chia seeds
For those winter months when your immune system has to contend with more infectious pathogens think of adding to your daily diet some soluble fiber by having more of these foods:
- Dried beans
- Oat bran
- Rice bran
- Citrus fruits
- Brussels sprouts
The bottom line is that a daily diet rich in fiber can significantly improve on all aspects of health. Maintaining is a case of being smart, choosing to add what is easily available and making sure that there is enough variety to keep it interesting.
Sources1. Effects of Dietary Fiber and Its Components on Metabolic Health
2. Fiber-Mediated Nourishment of Gut Microbiota Protects against Diet-Induced Obesity by Restoring IL-22-Mediated Colonic Health
3. A Dietary Fiber-Deprived Gut Microbiota Degrades the Colonic Mucus Barrier and Enhances Pathogen Susceptibility
4. Changes in Bacterial Community Structure in the Colon of Pigs Fed Different Experimental Diets and after Infection with Brachyspira hyodysenteriae
5. Inflammation, Immune Activation, and Cardiovascular Disease
6. The role of the immune system in atherosclerosis: molecules, mechanisms and implications for management of cardiovascular risk and disease in patients with rheumatic diseases
7. An apple a day? Study shows soluble fiber boosts immune system
8. The health benefits of dietary fiber: beyond the usual suspects of type 2 diabetes, cardiovascular disease and colon cancer
9. Fiber and Prebiotics: Mechanisms and Health Benefits
10. Fiber intake of the U.S. population
11. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses
12. Effects of high sugar and high fiber meals on physical activity behaviors in Latino and African American adolescents