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   
Healthy food high in protein. Meat, fish, dairy products, nuts and beans. Top view
  • 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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