= Microbiota-Accessible Carbohydrates

A MAC is a dietary carbohydrate that humans cannot digest, but that reaches the colon intact and can be metabolised by gut microbes.

In other words:

• Not digested by human enzymes
• Accessible to the gut microbiota
• Fermented by microbes, supporting their growth and function

This fermentation typically produces short-chain fatty acids (e.g. acetate, propionate, butyrate) and helps maintain microbial diversity and ecosystem stability.

Key clarifications

• MACs are not the same as “fiber” on a nutrition label
• They include complex, structurally intact carbohydrates, such as:
  • Certain fibers
  • Resistant starches
  • Oligosaccharides
• Refining, juicing, or ultra-processing can destroy MAC accessibility, even if fiber grams remain high

MAC-Rich Foods

• Lentils
• Chickpeas
• Black beans