A Broth + Co guide to how gut microbes ferment protein, fibre and plant compounds, why balance matters, and how to build meals that support microbial diversity.

 

Two Types of Fermentation in the Gut

Why This Topic Matters

Gut health conversations often split food into camps. Protein is placed on one side. Fibre is placed on another. Probiotics are treated as a third, separate solution.

Inside the gut, the picture is more interesting. Your microbiome does not think in product categories. It responds to what arrives: fibres, resistant starches, plant compounds, proteins, amino acids, fats, minerals, fluids and the food matrix that carries them.

One useful way to understand this is through fermentation. Gut microbes ferment different substrates and produce different metabolites. Some of the best-known products of plant fibre fermentation are short-chain fatty acids, including acetate, propionate and butyrate. Protein fermentation can produce a wider mix of compounds, including branched-chain fatty acids, ammonia, sulphur-containing compounds, phenols and indoles.

That does not mean protein is a problem. Protein is essential for growth, repair, muscle, immune function, enzymes, hormones and healthy ageing. The more useful question is this: what else is travelling through the digestive tract alongside it?

What Is Fermentation in the Gut?

Fermentation is microbial transformation. When parts of food reach the large intestine, resident microbes can use them as fuel or building material. In the process, microbes produce metabolites: small compounds that can interact with the gut environment and the wider body.

 

If the incoming materials are mostly diverse fibres and plant compounds, one pattern of microbial activity is encouraged. If the incoming materials are mostly undigested protein with very little fibre, a different pattern may become more prominent. Most real diets sit somewhere between those two extremes.

Plant Fermentation: Fibre Becomes Microbial Fuel

Plant fermentation occurs when microbes break down dietary fibres, resistant starches and other plant compounds that human enzymes cannot fully digest.

Foods that contribute to plant fermentation include vegetables, fruit, legumes, whole grains where tolerated, nuts, seeds, herbs and spices. These foods are not valuable only because they contain vitamins. They also deliver varied fibres and plant compounds that feed different microbial groups.

One of the most memorable ideas in gut health is this: you are not only feeding yourself. You are also feeding the ecosystem that helps process your food after you have eaten it.

Plant fermentation can produce short-chain fatty acids, including acetate, propionate and butyrate. These compounds are widely studied because they can act as fuels and signals within the gut environment.

 

Protein Fermentation: Normal, but Context Matters

Protein fermentation occurs when microbes break down protein, peptides and amino acids that reach the large intestine. This is a normal part of gut biology.

Protein-containing foods include meat, fish, poultry, eggs, dairy foods, legumes, tofu and tempeh, bone broth, collagen-rich foods and protein-containing mixed meals.

Some protein fermentation products are being studied because they may influence the gut environment. These include branched-chain fatty acids, ammonia, sulphur compounds, phenols and indoles. The story is not simple: some indole-related compounds may also have useful signalling roles, depending on the context.

This is why the goal is not to make protein fermentation disappear. The goal is to support a balanced microbial environment where protein is digested and used well, while fibre-rich plant foods continue to provide varied substrates for plant fermentation.

 

The Real Issue Is Not Protein. It Is Low-Diversity Eating.

Protein can become unfairly blamed in gut health conversations. In reality, the body needs protein throughout life: for children and teenagers who are growing, adults who are active or busy, pregnant and postpartum women, older adults, athletes and anyone recovering from daily physical stress.

The issue is usually not protein itself. It is a dietary pattern that is high in protein but very low in plant variety, fibre and whole-food diversity.

A steak with a colourful salad, lentils, herbs and extra virgin olive oil creates a very different gut environment from a high-protein meal eaten with almost no plant foods. A bowl of soup made with bone broth, legumes, vegetables and herbs is different again.

The pattern matters. The company protein keeps on the plate matters.

Why Microbial Diversity Matters

Different microbes prefer different substrates. Some are better at breaking down resistant starch. Others use fibres from legumes, vegetables or whole grains. Some specialise in plant polyphenols. Others help transform amino acids or use metabolites made by neighbouring microbes.

This is where the microbiome becomes less like a single machine and more like a community kitchen. One microbe starts the preparation, another uses the leftovers, and a third turns those leftovers into something new.

This process is known as cross-feeding. It helps explain why dietary diversity matters more than chasing one perfect gut-health food.

For a deeper look at this ecosystem approach, read Cross-Feeding Explained: How Gut Bacteria Work Together to Support a Healthy Microbiome.

Fibre and Protein Are Partners, Not Competitors

One of the most practical messages is that fibre and protein do different jobs. They should not be treated as competing priorities.

Protein provides amino acids for tissues, enzymes, immune proteins, neurotransmitter precursors, muscle maintenance, growth and repair. Fibre provides microbial fuel, supports dietary variety and helps shape the gut environment.

A meal that contains protein without plants may miss useful fibre and plant compounds. A meal that contains plants without enough protein may not support satiety, muscle or repair as well as it could. A strong everyday pattern brings them together.

Where Bone Broth Fits

Bone broth provides naturally occurring protein and collagen-derived amino acids, including glycine, proline and hydroxyproline. It can be used as a warm drink, a cooking liquid or a base for soups, stews, sauces, rice dishes and vegetable-forward meals.

From a gut-health perspective, bone broth is most useful when it helps people build better meals. It brings savoury depth, protein and functional hydration, while vegetables, legumes, herbs, spices and whole-food carbohydrates bring fibre and plant diversity.

That is the most balanced way to understand it. Bone broth is not a replacement for fibre-rich foods. It is a practical food that can help make fibre-rich meals easier, warmer and more satisfying.

For more on collagen-derived amino acids, see The Amino Acids in Bone Broth: What They Are and Why They Matter.

For the broader bone broth foundation, read Bone Broth Benefits: The Complete Guide to Gut Health, Protein, Recovery & Healthy Ageing.

Building a Microbiome-Friendly Plate

A microbiome-friendly plate does not need to be complicated. It simply needs more than one job happening at once.

Start with a quality protein source. Add two or more colourful plant foods. Include legumes, whole grains or resistant starch where tolerated. Use herbs, spices, olive oil, avocado, nuts or seeds for flavour and food-matrix variety. Use broth, water or tea to support hydration.

The point is not perfection. It is repetition. The gut responds to the pattern you build most often.

The Food Matrix Matters

Nutrients do not arrive in the gut as isolated dots on a nutrition panel. They arrive inside a structure: the food matrix. A lentil, a carrot, a piece of fish, a cup of broth and a spoon of olive oil all deliver nutrients in different physical and chemical forms.

That structure influences chewing, digestion, gastric emptying, nutrient release and what eventually reaches the microbiome. This is one reason whole-food patterns are different from simply adding isolated nutrients together.

To explore this idea further, read The Food Matrix Explained: Why Whole Foods Matter.

Practical Ways to Support Better Fermentation Balance

·   Add vegetables to protein meals rather than serving protein alone.

·   Use legumes in soups, stews, salads and slow-cooked meals if they suit your digestion.

·   Rotate plant foods across the week instead of repeating the same two vegetables.

·   Use herbs and spices generously for flavour and plant diversity.

·   Cook rice, quinoa or vegetables in bone broth when you want more savoury depth.

·   Build soups that combine broth, protein, vegetables and fibre-rich ingredients.

·   Increase fibre gradually if your gut is sensitive, and adjust according to tolerance.

Rainbow Lentil & Bone Broth Soup

A practical example of protein and plant diversity in one bowl. This recipe combines bone broth, lentils, vegetables and herbs so the meal contains savoury protein, fibre-rich plants and colour.

Serves 2 | Preparation 12 minutes | Cooking 25 minutes

Ingredients

·   500 ml prepared Broth + Co Beef Bone Broth

·   1/2 cup red lentils, rinsed

·   1 carrot, diced

·   1/2 red capsicum, diced

·   1 zucchini, diced

·   1 cup baby spinach

·   1 tablespoon extra virgin olive oil

·   1 small garlic clove, finely chopped

·   1/2 teaspoon ground cumin

·   1 tablespoon chopped fresh parsley

·   Sea salt and black pepper, to taste

·   Lemon wedge, to serve

Method

·   Warm the olive oil in a medium saucepan over low to medium heat.

·   Add the garlic and cumin, then cook for 30 seconds until fragrant.

·   Add the carrot, capsicum and zucchini. Cook for 3-4 minutes, stirring occasionally.

·   Add the lentils and bone broth. Bring to a gentle simmer.

·   Simmer for 15-18 minutes, or until the lentils are soft and the vegetables are tender.

·   Stir through the baby spinach and parsley, then cook for 1 minute until wilted.

·   Season to taste and serve warm with a squeeze of lemon.

 

Try the Recipes

For more practical meal ideas, explore:

Vegetable Forward Soups and Broths

The Power of Soup: How One Pot Can Support Immune Health, Eat More Vegetables & Reduce Food Waste

collection of nourishing recipes

Frequently Asked Questions

What is protein fermentation?

Protein fermentation occurs when gut microbes break down protein, peptides or amino acids that reach the large intestine. It is a normal microbial process, but its balance can be influenced by the wider diet.

What is plant fermentation?

Plant fermentation occurs when gut microbes break down fibres, resistant starches and plant compounds from foods such as vegetables, fruit, legumes, grains, nuts, seeds, herbs and spices.

Is protein fermentation bad?

No. Protein fermentation is not automatically bad. Protein is essential for health. The practical focus is to avoid low-diversity eating patterns where fibre and plant foods are consistently missing.

Why does fibre matter for gut health?

Some fibres act as substrates for gut microbes. When microbes ferment these fibres, they can produce metabolites such as short-chain fatty acids. Learn more in Short-Chain Fatty Acids Explained: How Your Gut Microbes Turn Fibre into Health-Supporting Compounds.

Can bone broth fit into a gut-friendly diet?

Yes. Bone broth can be used as part of a balanced dietary pattern, especially in soups, stews and meals that also include vegetables, legumes, herbs and other fibre-rich foods.

What is the simplest way to support microbial diversity?

Eat a variety of whole foods across the week: quality protein, vegetables, fruit, legumes, herbs, spices, nuts, seeds and whole-food carbohydrates where tolerated.

Summary

Protein fermentation and plant fermentation are not enemies. They are different microbial processes shaped by what reaches the gut. Protein remains essential for the body, while fibre-rich plants help feed the microbial ecosystem. The most useful dietary pattern is not extreme. It is varied, balanced and repeatable: quality protein, colourful plants, legumes or whole-food carbohydrates where tolerated, herbs, spices, hydration and meals that make healthy eating easier to sustain.