Resistant proteins: what are they and what are they doing to gut bacteria?

Mmmmm, doesn’t that golden-brown fried chicken get your mouth watering…  but it turns out that the bacteria in your gut may not enjoy it as much as you do.

Foods like baked goods, fast food, fried foods and processed meats are common in what we call a Western-style dietary pattern [1]. Something that these food products have in common is that they undergo high-heat cooking/processing prior to consumption. The Maillard reaction is a chemical reaction that takes place during high-heat processing (such as roasting, frying or toasting) and creates linkages between proteins (amino acids) and carbohydrates (sugars) within the food. This reaction produces the desirable golden-brown colour, flavours, aromas and textures in food products but also causes proteins to become less digestible. These “resistant proteins” pass through to the colon and are fermented by the gut bacteria.

We currently have little understanding of how resistant proteins work, the products that are produced when gut bacteria ferment these resistant proteins, or the resulting impact on gut bacteria composition.  This may be an important link between the Western diet and chronic disease.  Dr Margaret Murray and team have explored the effects of a diet high in resistant protein on the composition of the gut bacteria and chronic disease markers. 

It was hypothesised that a diet high in resistant protein contributes to poorer health by altering gut bacteria composition and the metabolites produced when the gut bacteria ferments protein. Dr Murray and team completed a pilot study using pigs to find out the effects of a standard diet versus a diet high in resistant protein on the composition of faecal bacteria and biomarkers of disease risk. The standard and resistant protein diets were matched for energy, nutrient composition and total protein. The feed for the resistant protein diet group underwent high-heat processing to trigger the Maillard reaction and produce digestive resistant proteins.  

After four weeks on the respective diets, Dr Murray and team observed a difference in the composition of faecal bacterial communities between the pigs that were fed the standard diet and the resistant protein diet. The standard diet group had higher levels of bacteria such as Kandleria, Butyrivibrio, Streptococcus, Catenibacterium and Megasphaera genus.  Whereas, the resistant protein diet group had higher levels of Prevotella, Lactobacillus sp and Blautia genus.This shift in the bacterial communities was likely a result of the increased amount of protein in the colon available for bacterial fermentation for pigs on the resistant protein diet.

In line with changes in bacterial composition, the production of acetic acid, a short-chain fatty acid, was lower in the resistant protein diet group. Short-chain fatty acids play many important roles in supporting the health of the digestive tract and general health [2]. Acetic acid is a beneficial short-chain fatty acid that is produced when gut bacteria ferment fibre [2]. The reduction in acetic acid production on the resistant protein diet was likely because of the increased availability and use of protein as a fermentation substrate, instead of fibre.  

The lower level of short-chain fatty acids was consistent with the observed elevation of pro-inflammatory markers (homocysteine, neopterin) in those on the resistant protein diet. This suggests that a diet containing a lot of resistant protein (from lots of processed foods), causes a change in our gut bacteria; and this leads to a change in the metabolites produced by our gut bacteria, which contributes to chronic inflammation.

While the diet in the current study represented an extreme example of high levels of resistant protein, there are smaller amounts of resistant protein present in most protein-containing processed foods.  Dr Murray says that habitual consumption of highly processed protein-containing foods over a long period could drive the same biological processes observed here and contribute towards chronic low grade inflammation. 

With the globalisation of the food supply, a highly processed, Western-style dietary pattern is becoming common around the world and contributing to increased chronic inflammation and

diet-related chronic disease risk [1]. These results further highlight the importance of consuming less processed foods and more whole foods, where possible, to support a healthy gut and reduce chronic disease risk factors.

By Margaret Murray

Dr Margaret Murray is a Teaching Associate in the Department of Nutrition, Dietetics and Food and Research Fellow in the School of Chemistry at Monash University.  Her research investigates the health effects of food-based bioactives on chronic disease and mental health.  Other interests include exploring how food systems can be tailored to support human and environmental health and teaching in the Master of Food Science and Agribusiness.  Access Margaret’s research profile here.

 

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Publication information

Murray M, Coughlan M, Gibbon A, Kumar V, Marques F, Selby-Pham S, Snelson M, Tsyganov K, Williamson G, Woodruff TM, Wu T, Bennett E.  Reduced growth, altered gut microbiome and metabolite profile, and increased chronic kidney disease risk in young pigs consuming a diet containing highly resistant protein. Frontiers in Nutrition, https://doi.org/10.3389/fnut.2022.816749 

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References:

1. ALjahdali, N. and F. Carbonero (2019). "Impact of Maillard reaction products on nutrition and health: Current knowledge and need to understand their fate in the human digestive system." Crit Rev Food Sci Nutr 59(3): 474-487.
2. Wang, M., et al. (2019). "In vitro colonic fermentation of dietary fibers: Fermentation rate, short-chain fatty acid production and changes in microbiota." Trends Food Sci Technol 88: 1-9.