Low Carb Diet and Gut Health: Are we doing more harm than good?

vegetablesLow-carb diets are all the rage right now, and with good reason. They have shown promising results in promoting weight loss and encouraging people to eat less white flour, sugar, and other unhealthy foods. Hard to argue with that. I’m on board.

What’s the big deal? Well, research is now indicating that diets such as these, which are very low in fiber, might be a problem when it comes to the health of our gut. While we know fiber is important for regularity, supporting healthy blood sugar, and increasing satiety, did you also know that fiber feeds your healthy gut bacteria, or the microbiome as it is commonly known?

The problem is, as seen via research, that this decline in fiber corresponds with a decline in microbiome diversity. In simple terms, over time we starve out many beneficial strains of healthy glut flora residing in our digestive tract. Additionally at the same time we promote more of the unhealthy and less desirable strains.

For example, a recent study looked at microbiome diversity among rural Africans and the average US population. They found much greater diversity and more beneficial strains of bacteria in the guts of Africans. Not exactly surprising. What is interesting is that when they switched their diets and fed this group of Africans the Standard American Diet for two weeks, stool analysis showed a significant decrease in the “good” bugs.1 This was after only two weeks! What does this say for those of us consuming low fiber diets for weeks or years on end?

This creates some cause for concern because research has shown that the health of our microbiome influences the health of the host.2 In other words, our personal health is influenced by the bugs living in our digestive tract. For example, Crohn’s Disease and other inflammatory bowel diseases seem to be linked with alterations in the microbiome. 3  Also more and more studies are linking obesity and increases of certain types of bacteria in the guts of Americans. In rats, we can directly influence their weight by the type of bacteria we put in their system!4 Fascinating stuff, and yet scary at the same time.

If you are one of those embarking on a low carb diet, don’t fret! It can be done in a healthy way to support your health goals, while at the same time supporting  your microbiome. Clearly the main goal is to keep up the fiber in whatever way possible. Let’s talk about some ways to do that.

Main key when going low carb:  Include as many fiber sources as you can!

  • Fruit: Choose the lower carb ones like berries, avocado, tomatoes. For higher carb fruits, keep the portions smaller.
  • Vegetables: Make sure to get as much vegetable intake as you can every day! Many veg options are low carb and can be included in abundance.  Add lots of low carb leafy greens and cruciferous (broccoli, cauliflower), or consider green beans, zucchini, peppers, etc. Consume starchier choices like squash, carrots, peas and potatoes in smaller amounts.
  • Eat nuts and seeds! These are a great low carb option with protein and fat but which also have an appreciable amount of fiber. Think almonds, walnuts, cashews, flax seed, chia seed, hemp seed, pumpkin seeds…. you get the idea.
  • Eat beans! Yes they do have carbs, but again, watch the portions. Generally about ½ cup of beans equals 15g of carb, so you can have beans and still keep the carbs in check.
  • Don’t forget about fermented foods! These can help replenish and support a healthy microbiome. Try adding a daily dash of sauerkraut, kefir, cultured yogurt, kombucha, pickled veggies, or tempeh.

What about the Ketogenic Diet?

Yes, I realize there is a big push towards the “keto” diet as of late. If you are not aware of this trend, it’s a diet that decreases carbs to the extent that it puts the body in ketosis. This encourages the body to burn fat as fuel, producing ketones, which the body can use in a similar way to carbs. It is extremely low carb, obviously, and followers often test their urine to measure ketones and thereby ensure they are in the state of ketosis. Many health benefits, including weight loss, improved cardiovascular health and neuro-protective benefits have been purported by this plan, and there are many functional and integrative health professionals who are choosing this as a way of life for health and longevity.

The problem is that, if not followed correctly, one can easily over-consume on foods like animal proteins, dairy (like cheese and butter), eggs, artificial sweeteners, and low-carb processed concoctions. Very quickly the diet becomes reduced and limited to a set of foods which are low in carb yet also low in fiber, thus potentially eradicating many healthy bacteria strains from one’s digestive tract.

The keto diet can be done successfully, however, and without drastic harm to the microbiome, if done appropriately, utilizing some of the tips provided above. Also some supplementation with probiotics or increased servings of fermented foods is a good idea.

Hopefully for you low-carb lovers, your fears have been allayed. Look for ways to get in that fiber, enrich your diet with fermented foods, and consider supplementation when needed.

  1. O’Keefe SJ, Li JV, Lahti L, et al. Fat, fibre and cancer risk in African Americans and rural Africans. Nat Commun. 2015;6:6342.  https://www.ncbi.nlm.nih.gov/pubmed/25919227
  2. Marchesi JR, Adams DH, Fava F, Hermes GD, Hirschfield GM, Hold G, Quraishi MN, Kinross J, Smidt H, Tuohy KM, Thomas LV, Zoetendal EG, Hart A. The gut microbiota and host health: a new clinical frontier. Gut. 65:330-9, 2016. https://www.ncbi.nlm.nih.gov/pubmed/26338727
  3. Sartor RB. Microbial influences in inflammatory bowel diseases. Gastroenterology. 134:577-94, 2008. https://www.ncbi.nlm.nih.gov/pubmed/18242222
  4. Turnbaugh PJ, Ley RE, Mahowald MA, et al. An obesity-associated gut microbiome with increased capacity for energy harvest. Nature. 444(7122):1027-31, 2006. https://www.ncbi.nlm.nih.gov/pubmed/17183312

If you are thinking about starting a lower carb way of life but need a little guidance, please ask! I would love to help you get a plan in place that cuts down on the carbs but keeps nutrition at its maximum.


Danielle VenHuizen

Registered Dietitian, Certified LEAP Therapist