Microbiota-Accessible-Carbohydrates, or MACs, are particular types of carbohydrates that resist digestion, end up in your large intestine and do all sorts of good for your gut bacteria.

While most nutrients are absorbed in your small intestine, MACs are unable to be digested, nor absorbed, and in turn, end up travelling to your colon.

Your colon is inhabited by trillions of bacteria, which are known as your gut microbiota.

Although you (your body) cannot digest MACs, the bacteria living inside your gut can. They do this via producing specialised enzymes that break the MACs down. This is essential, because MACs represent the major energy source for your colonic bacteria.

Basically, MACs are fermentable fibres and indigestible short chain carbohydrates. They are often referred to as prebiotics.

Note: not all fibres are fermentable, just particular types.


MACs are found in garlic, onion, legumes, green bananas, cooked and cooled potatoes, wheat bread and barley... to name a few.


When MACs reach your colon they are fermented by your bacteria. This fermentation results in the production of short-chain-fatty-acids (SCFAs), including acetate, propionate and butyrate. SCFAs are the primary fuel for your gut cells (colonocytes).


Not only are your gut bacteria important for digesting MACs, but they also play numerous roles in your immune function, metabolism, gut health (e.g. structural health), mental health and nutrient production. Your gut bacteria also likely play a role in preventing non-communicable diseases, such as allergies, cancers, inflammatory conditions and autoimmune conditions.


Since the early 1900s, many countries, mostly Western, have experienced the invasion of processed foods. Over time, these processed foods have snow-balled into dominating most westerners food choices.

Food processing refers to the action of performing mechanical and/or chemical operations on raw food in order to change or preserve it. On the most part, this involves refining wholefoods (removing fibre and nutrients) and adding unhealthful ingredients (sodium, sugar, fats and additives).


One of the most unfortunate aspects of food processing is the removal of fibre, which includes the removal of MACs.


Western diets today are characterised by processed foods that are low in MACs. Think white foods and sugar-added packaged not-so-goods.

In recent decades, the prevalence of non-communicable diseases, including allergies, autoimmune and inflammatory diseases, have dramatically risen, unsurprisingly in line with increased unhealthful behaviours. This includes the unhealthful drastic drop in the consumption of MACs.


The recommended daily intake for dietary fibre (inclusive of MACs) is 30 grams per day. The average Western consumes less than half (<15grams) of this requirement. In contrast, people in traditional societies consume up to 50-120 grams of MACs per day.


Those who consume a high intake of MACs tend to have a much more diverse gut microbiota.


This means they have significantly higher numbers of gut bacteria, as well as greater diversity in bacteria species types.

A diverse gut microbiota is associated with overall better health, while a low diversity has been associated with numerous diseases, including obesity, type 2 diabetes, inflammatory bowel diseases, rheumatoid arthritis and asthma.

The composition and function of your gut microbiota are highly dependent on the availability of MACs.

Because of food processing, the MAC content in Western diets has significantly decreased.


Overall, to improve your gut microbiota health, aim to meet your dietary fibre requirements by consuming a variety of (unprocessed) plant-based wholefoods that are high in MACs. All plant foods do contain fibre, however some are a bit richer than others.


The key is to eat a large variety of plant foods.



  • Amaranth, barley, quinoa, teff, buckwheat

  • Almonds, nut butter

  • Hemp seeds, pepitas, flaxseeds, sunflower seeds, chia seeds

  • Lima beans, adzuki beans, black beans, lentils, kidney beans, mung beans

  • Collard greens, cauliflower, brussel sprouts

  • Raspberries, blackberries, pear, guava, persimmions

  • Edamame

  • Avocado

  • Prunes, figs, dates

  • Oat bran, wheat bran, all-bran

NOTE: If you do not normally eat much fibre, aim to increase your fibre intake slowly and ensure to drink plenty of water.