The Role of Protein in the Diet – the history of man’s diet

What all low carb diets have in common is that they are low in carbohydrates  and high in healthy fats, but they vary with respect to the amount of  protein  and fat. This article is part 2 in the series The Role of Protein in the Diet and focuses on the evolutionary history of foods and how we have adapted (or not!) to these foods.

The first article in this series titled The Role of Protein in the Diet – the problem with carbs is located here.

This article is based largely on a lecture given by Dr. Donald Layman, PhD – Professor Emeritus from the University of Illinois (Nutrition Forum, June 23, 2013, Vancouver, British Columbia, Canada)

It is almost universally accepted that when man was a hunter-gatherer, we ate largely an animal-based diet and this was distributed as 60% animal protein and 40% plant protein.  Naturally, there was some variation, depending on where people lived.  Those in the tropics tended to eat more plants and fish and the Inuit, who lived in northern climates had less green plants in their diet.

If we look at contemporary agriculture over the past 400-plus years out of the previous past thousands of years, what has absolutely changed is the appearance of cereal grains.

These were totally non-existent in the history of man’s diet previous to the agricultural revolution.

Legumes, such as peas, beans, chickpeas, lentils, etc. were also totally non-existent in the history of man’s diet previous to the agricultural revolution.

Sugars (outside of the little bit in wild honey or in the occasional fruit or berries), plant oils, alcohol and dairy products were simply non-existent before the agricultural revolution.

Our bodies did not evolve to see those things.

What does this means in terms of the foods we eat?

Let’s take fiber as an example. In the past, the plants man ate were very fibrous, both vegetables and fruit. Looking at our current cultivated plants wild cousins, provides some idea:

wild carrot

The earliest known carrots are thought to have been grown in the 10th century in Persia and Asia Minor and are believed to have originally been purple or white with a thin, forked root — like those shown here.


Bananas as we know them now are nothing like bananas our ancient ancestors ate. Modern bananas came from two wild varieties, Musa acuminata  and  Musa balbisiana, both of which were very fibrous and had large, hard seeds, like the ones seen in this photo.

The plants we ate traditionally were high in soluble fiber that were easily digested and broken down to form short chain fatty acids (SCFA) which acted in our bodies as prebiotics, as these SCFA are very good fuel for the bacteria in our colon.

The agricultural revolution changed all that, with the domestication of plants, and the shift to a diet high in cereal grains; rice, corn, spelt, etc. Debate rages about consuming more whole grain cereal grains, but those contain largely insoluble fiber, which are not well digested.  They don’t break down easily to SCFA and impact our microbiome (the healthy bacteria that lives in our colon).  These cereal grains typically come with a high Glycemic Index (GI) which means they have a strong effect on a person’s blood glucose level, raising it substantially.

Our bodies developed certain metabolism patterns based on the foods in our ancient diet.

  1. Extensive and elaborate pattern for handling protein: The human body has developed very elaborate patterns for handling protein digestion, metabolism and elimination. We have a very high satiety to protein (the feeling or state of feeling full) such that we won’t over eat it. According to Dr. Layman[1] it’s the only nutrient that causes us to stop eating it.
  2. Fat is a passive nutrient: Contrary to the common belief, fat is a very passive nutrient. It allows what happens to it, without an active response or any mechanism of resistance. Fat in and by itself has very little effect on our body. We store it effectively and break it down effectively and this is what allowed us to survive in the wilderness as hunter-gatherers.The nutrient that is odd in this mix is carbohydrates.
  3. Little evolutionary exposure to carbohydrate: Looking at our dietary history, we have comparatively very little exposure to carbohydrates. According to Dr. Layman, carbohydrates are highly toxic to the bodyGlucose has to be rapidly cleared after we eat it and the only mechanism we have to protect us from carbs is insulin (which acts to move the resulting glucose out of our blood and into our cells).

It’s important to put carbohydrates into perspective in terms of the biological systems that we have for handling them.

The traditional teaching is that carbs are handled in the muscle – which is true, if one exercises 2-3 hours per day.  North Americans are typically exercising that much at in the US, 75% of people are considered sedentary – that is, they have a lifestyle with little or no physical activity.

The carbs we eat at breakfast for example, top up our glycogen stores in our muscle, making us ready for fright or flight.

So let’s say we ate atypical breakfast that has 70 g of carbohydrate in it;

1/2 cup (125 ml) of cold cereal
1 slice of whole grain toast
1 medium orange
1 cup (125 ml) of low-fat milk
2 tbsp (30 mL) peanut butter
coffee or tea

Then, we sat in front of the computer all morning, so chances are we didn’t use any of the carbs from breakfast, and our glycogen stores are still full.

We get to lunch and eat another 100 g of carbs.

Our glycogen stores are still full, so where is that glucose going to? It has to go to fat.

When we have carbohydrates in excess, we make fat out of them.

The matter of carb regulation is very important to think about, because  blood sugar is one of the most tightly regulated substances in the body. We regulate our blood glucose in a very narrow range; between about 3.9-5.5 mmol/L (70-100 mg/dL).

Why does this matter?

Metabolic Syndrome (also called Syndrome X) says it matters a huge amount.


1 – Layman, Donald, The Evolving Role of Dietary Protein in Adult Health, Nutrition Forum, British Columbia, Canada, June 23, 2013

2 – Lewis, Tanya, What Fruits and Vegetables Looked Like Before Domestication, Business Insider, November 16, 2017,