What are grains and why are they avoided on the Paleo diet

Simply put, grains are the hard, edible kernels that grow on grass-like plants and processed into many forms for different uses. They are a staple food in most countries and there are many different varieties, the most common being:

  • Wheat
  • Corn
  • Oats
  • Rice

The grain kernel is made up of three main parts: 

  • The Bran is the hard outer layer or shell.
  • The Germ is the core of the seed that provides nutrients when it sprouts and grows
  • The Endosperm provides a starchy food source for the growth of the seed.

Before we take a look at the role of grains in the modern day diet, I would just like to point out that for a lot of people eating grains is fine and they have no issues. This article plans to outline the issues with grains that some people do have, in particular, those with autoimmune diseases.

Grains are a controversial food in modern society, as they are eaten by all populations but have been found to contain toxic anti-nutrients, i.e. substances that prevent your body from absorbing the nutrients it needs and in turn creates havoc in our systems. At the simplest level, a toxin is something capable of causing disease or damaging tissue when it enters the body.

In their book ‘The Perfect Health Diet’, Paul and Shou-Ching Jaminet apply the economic principle of declining marginal benefits to toxins:

It implies that the first bit eaten of any toxin has low toxicity. Each additional bit is slightly more toxic than the bit before. At higher doses, the toxicity of each bit continues to increase, so that the toxin is increasingly poisonous.

Most of us won’t get sick from eating a small amount of sugar, grain, industrial seed oil etc. But if we eat those (anti-nutrients) in excessive quantities, our risk of developing modern diseases rises significantly.

So you’ve been eating grains all your life and you’re not dead yet, right? The human body is an incredibly resilient biological machine, and yes, you could go through your entire life eating grains and never get one of the many debilitating autoimmune diseases. In the end, you may be lucky. But by combining genetics, your environment and the toxins ingested, you may find yourself among the many who are indeed affected.

Grains are the reproductive materials of plants and if consumed in their entirety by a predator, the plant would rapidly become extinct. Thus, plants have evolved three major strategies to resist predation, so that their reproductive material can survive to produce the next generation. These three mechanisms are:

  1. Toxic compounds to discourage predation.
  2. Structural barriers to predation, such as spikes or thorns found in cactus or hard impervious shells such as those found in coconuts and brazil nuts.
  3. A sweet, attractive out layer that encourages predation, combined with hard, small seeds within that layer that are impervious to the digestive tract of the predator and pass through the digestive tract into the faeces.

Grains most typically have evolved toxic, anti-nutritional compounds to prevent predation and a few of these include:

  • Lectins
  • Saponins
  • Protease inhibitors
  • Phytic acid

These compounds are the plants chemical defences and can cause digestive irritation in the consumer:


Lectins are special proteins that exist in many types of foods, but only certain types are toxic. Gluten is the most famous lectin but non-gluten grains contain other lectins that many people have poor reactions to.
A high consumption of lectins can lead to intestinal damage and compromised intestinal bacteria.


These compounds found in grains are also problematic to humans. They are designed to protect the seed so that it can survive to pass on the plant’s genetic line. Saponins can damage enterocytes (cells that line your gut and control what passes in and out of it).

Protease inhibitors

These inhibitors are the seed’s last line of defence and if ingested, they will prevent your digestive enzymes from properly breaking down the proteins found in the seed. At the same time, they prevent your body from breaking down proteins found in everything else in your gut. Protease inhibitors are especially damaging to the pancreas which produces the digestive enzymes that they neutralize.

Phytic Acid

It binds to minerals in our food and prevents us from absorbing them. Phytic acid can also interfere with digestive enzymes and otherwise irritate your gut.

To summarise

Grains contain anti-nutrients that can negatively affect the digestive system, mostly in health compromised systems.

Grains are very simple carbohydrates so they break down into sugar quickly and can cause a spike in your blood sugar levels resulting in a spike in insulin levels.

High insulin levels prevent your body from burning fat because your body is caused to focus on converting the excess glucose in your bloodstream into energy and storing the excess as fat.

Constantly eating simple carbohydrates can lead to chronic high blood sugar levels, which can lead to obesity problems and pre-diabetic symptoms.

According to some scientists, as a species, humans have no cereal grain requirement for proper nutrition as we can obtain all required nutrients from meats, fish, seafood, poultry, fresh fruits, vegetables and nuts. This is pointed out in a paper written by Loren Cordain - PhD and published in the ‘American Journal of Clinical Nutrition in 2005’. ¹

1. Cordain L, Eaton SB, Sebastian A, Mann N, Lindeberg S, Watkins BA, O’Keefe JH, Brand-Miller J. Origins and evolution of the western diet: Health implications for the 21st century. Am J Clin Nutr 2005;81:341-54