Episode 77 – Are High Protein Diets Bad For Gut Health?

 What is “Gut-Health”? 

  • No clear definition. But it is a combination of stuff including: 
  • 1) The ratio/diversity of bacteria in the gut. But even this is not super clear cut.  
  • 2) GI symptoms – good gut health = lack of GI symptoms  
  • But there is disconnect e.g. eating highly fermentable foods can be great for the good bacteria, but bad for the symptoms in some cases. 

How Do We Measure it? 

  • Measuring the abundance of “good types of bacteria.” Measuring the abundance of “pathogenic bacteria.” Measuring the diversity of bacteria. Monitoring GI symptoms. 
  • The bacteria side of things is often measured in stool samples. 

How Do We Define a High Protein Diet?   

  • A diet that is >25% of calories from protein (above the AMDR). Another one could be >1.4g/kg/day or a similar type of number) 

What Changes are Reportedly Seen on a High Protein Diet? 

  • Decrease in the bacteria that produce short chain fatty acids 
  • Reduction in diversity of microbiome 

What Relevant Research is there on the Topic? 

The Korean Study  

  • A study published in 2019 compared faecal microbiota characteristics amongst bodybuilders, distance runners and a control group of sedentary men.  
  • They assessed the relationship between the gut microbiome and body composition, athlete type and dietary intake.  
  • Amongst bodybuilders there was a general reduction in bacteria that produced short-chain fatty acids. These are well-known for their positive role in gut health. 
  • It was suggest that this was for a couple of key differences that were apparent between the bodybuilders and the other groups –  
  • A) they had the highest protein intake (236g VS 103g in runners & 70g in control) 
  • B) Their protein to carb ratio was double the other groups as well which could be a factor  
  • C) Whilst they had the highest fibre intake by a few gram on average, the mean intake was only 19g per day – it was suggested that such a high protein intake in combination with a subpar fibre intake, may be the biggest issue when it comes to these high protein diets and gut health   
  • A study by Clarke et al. From 2014 looked at protein intake and gut microbiome diversity in rugby players 
  • They found that as protein intake in rugby athletes increased, the gut microbiota diversity actually increased! So a higher protein intake does not always have to have a negative impact on gut health. 
  • The biggest difference between the diet of the rugby athletes and the bodybuilders and runners in the Korean study was that the Rugby athletes had a higher carbohydrate and fibre intake. Likely protecting them from the potential effects of a high protein diet.  

Can We Offset these Changes in Any Way? 

  • High fibre diet. A solid target to make sure it scales with higher calorie intakes is at least 12-15g of fibre per 1000kcal. 
  • Diversity of plant based foods 
  • Keeping fat intake <40% of total calories. Keep saturated fat <10%. 
  • Limit high fat red meat and processed meat – high fat/cholesterol intake from meat is linked with lower bifidobacteria levels 

Summary – Are High Protein Diets Bad for Gut Health? 

  • The health effects of increased protein fermentation are not entirely clear. But high protein, low carbohydrate and fibre diets are likely harmful to the gut microbiome.  
  • For those who are on a high protein diet, for long-term gut health, there should at least be a focus on adequate fibre, a higher carbohydrate diet & high plant food diversity. 

Relevant Links/ Resources

Studies Mentioned:

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