FFF 146: How Popular Diets Impact Gut Health – with Dr Gabrielle Fundaro


Scott and Dr. Gabrielle Fundaro talk about the gut microbiome, the effects of vegan diet, vegetarian diet, and omnivorous diet on the microbiome, and way to improve your gut health.

Gabrielle has a Ph.D. in gut microbiome and skeletal muscle metabolism. She spent four years serving as an assistant professor of exercise science, primarily teaching sports nutrition. She then transitioned to coaching full-time and now a Renaissance Periodization coach. She has a consulting business both in Ph.D. and nutrition. She travels around the world delivering seminars and providing evidence-based information on the gut microbiome and diet psych.

Use of the Term“Evidence-Based”

Gabrielle defines an evidence-based recommendation as a recommendation based on the breadth and depth of evidence. It’s about looking at the big picture and recognizing the limitations and the strength or weakness of the evidence. What models are we looking at and how applicable is the specific article to the human body? The details really matter.

Should You Remove Dairy From the Diet?

There’s a misunderstanding about what could actually end up in the milk. People think that if an animal is provided with antibiotics or hormones, those will then enter the milk. So they think they need to remove the dairy from the diet.But when we really look at human populations and clinical outcomes, that’s not a reason to eliminate dairy.

That being said, there is validity in removing dairy due to lactose intolerance. But it can actually change over time. People can become more or less lactose-tolerant while some types of dairy have more or less lactose.

For instance, aged hard cheese or a cultured beverage where lactose has been broken down will be more tolerable than if you had a soft cheese or regular milk that’s very high in lactose. Unless the person is lactose-intolerant, there’s really no reason to remove dairy.

Additionally, there is strong evidence to show that regular dairy ingestion has anywhere from neutral to modest benefit for things like the risk of cardiovascular disease and improved body composition.

Gabrielle recommends including dairy in your diet if you can digest it. There are other forms of dairy that are lower in lactose and you’d be able to tolerate those. Lastly, it’s totally valid if removing lactose is for ethical concerns.

Benefits of the Vegan Diet to the Gut

A recent study was released comparing vegetarian, omnivorous, and vegan diets. They found that the microbiome changed appreciably as soon as the foodstuff entered the large intestines. Those on the animal-based diet had microbiomes that looked very different from baseline. Whereas those on the plant-based diet had microbiomes that didn’t change very much.

Diversity is neither good nor bad. The microbiome simply adapts to dietary changes. They found that there wasn’t a huge change in diversity between omnivores versus vegans and vegetarians.

One sensitive group of  bacteria are bifidobacteria that are very sensitive to changes in dietary fiber intake. Once there is a deficiency in dietary fiber, their levels tend to fall. This could matter long-term since bifidobacteria are considered to be a beneficial group of bacteria.

Another group is the bacteroides that are dynamic and use whatever is available. You don’t want these to proliferate as they can break down the mucus layer that protects the cells of our intestines.

Regardless of the type of diet, fiber intake is probably the most important aspect to think about. It happens that a vegan diet is higher in fiber. But it doesn’t mean we can’t get that with a vegetarian or omnivorous diet, or even a ketogenic diet, provided it has sufficient fiber. Focus more on these rather than the ethos of a specific diet.

The Carnivore Diet and Nutrient Deficiencies

If there is a fiber deficiency, the microbes need to find the carbohydrate source and one source is that mucus layer covering the intestinal cells. So we start to see a shift, particularly a reduction of the mucus layer. Hence, low-fiber diets are not recommended long-term as there could be potential for negative outcomes.

Looking at the carnivore diet, you’d see an uptake of bacteria that are able to metabolize amino acids and break down that mucus layer. And there’s a loss of bacteria that are good at fermenting short-chain fatty acids.

Moreover, the lack of compliance or the duration of the diet is preventing them from developing severe clinical nutrient deficiency. Also, it takes a long time to develop clinical nutrient deficiency. This goes to show how resilient the human body is and we’re not as fragile as people like to think. We can survive with significant dietary deficiencies for a relatively long period of time.

People think that a carnivore diet is good for them due to the changes in their bowel habits. But that doesn’t necessarily mean that your microbiome is doing well or that your intestinal health is not at risk in the short-term just because you see a reduction in gas and bloating.

Probiotics and Prebiotics Supplementation

We don’t necessarily need to supplement with prebiotics since we can get plenty of it in our diets. They come in the form of microbe-accessible carbohydrates. These are mostly fibers not accessible to us like fruits, vegetables, whole grains, and legumes.

The probiotics seem to have modest, specific benefits. They’re strain-specific and work for a pretty limited number of ailments like irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), traveler’s diarrhea, and antibiotic-associated diarrhea. These are improved by probiotics supplementation with specific strains of probiotics.

One example is the S. boulardii, which is a yeast, not bacteria. It’s incredibly beneficial for reducing symptoms of traveler’s diarrhea and antibiotic-associated diarrhea. Bifidobacteria are beneficial for IBS and IBD, and potentially, upper respiratory tract infection.

There is no need for supplementation unless you’re taking a specific strain to address a specific issue.

Other Ways to Improve Gut Health

Limit overall dietary fats to less than 40% of your calories. Omega-3 fatty acids are beneficial. Make sure you’re eating vegetables at every meal. Exercise enough but not too much. Focus on mental health, stress management, and sufficient sleep. These play a role in shaping the microbiome and just overall digestive comfort.

If you have issues, go to a gastroenterologist and you might want to work with a registered dietitian. Don’t waste money on tests for food sensitivities or the DNA tests for your gut.

  • Gabrielle’s powerlifting stint
  • What it means to say evidence-based
  • Should you remove dairy from your diet?
  • Vegan diet and the gut microbiome
  • Carnivore diet and nutrient deficiencies
  • Is there a need to supplement yourself with prebiotics and probiotics?
  • Ways to improve your gut health
Quotes & Take-Aways

An evidence-based recommendation would be a recommendation based on the breadth and depth of evidence

When we really look at human populations and clinical outcomes, that’s not a reason to eliminate dairy. 

Lactose intolerance can actually change over time. 

There is validity in removing lactose and testing it back in to determine what level you can tolerate it.

Unless the person is lactose-intolerant, there’s really no reason to remove dairy.

A change in diversity is really neither good nor bad. It’s saying there’s a change in the weather.

Regardless of the type of diet, fiber intake is probably the most important aspect to think about.

We are not as fragile as people like to think. We can survive with significant dietary deficiencies for a relatively long period of time.

If you don’t have one of those ailments, there’s not a kitchen-sink antibiotic that you take like a multivitamin every day. That would be a huge waste of money.

Connect with Gabrielle:

Thanks for listening and the support – if you enjoyed this episode, I hope you can leave the podcast a rating and review on iTunes, and if you haven’t subscribed yet, this is the best time to do that too. This will help the show to get up in the rankings.

Scott is the owner and founder of Food For Fitness. He is a fat loss coach, speaker and fitness writer with a masters (MSc) degree in Applied Sports Nutrition.