This article is Part II in a series titled The Role of Protein in the Diet and looks at macronutrients in our diet from an evolutionary perspective.
Over the course of man’s existence, there have been a number of major shifts in the human diet and with that change, came the necessity of the body to adapt by producing enzymes capable of digesting and absorbing nutrients from these novel foods. This required the human genome (our genes) to adapt, evolve and change [1]. This takes time.
In the ~4.4 million span of mankind’s existence, solid evidence for use of human-controlled fires, which would have given us the ability to cook our meat is only about 800,000 years old [2] with less certain sites dating back 1,500,000 years [3,4].
The origin of domestication of animals is considered to be ~10,000 – 12,000 years and represent another relatively recent shift in the human diet [1], moving mankind from a hunting and gathering species, to an agricultural one. With this shift came the need to domesticate crops, which dramatically changed the human diet. The innovation of human agriculture greatly reduced diversity in the human diet. Instead of ‘food’ being what hunter-gatherers were able to find, ‘food’ was what each group grew and raised.
Of even more significance, it is estimated that 50%—70% of calories in the agricultural diet are from starch (carbohydrates) alone [5]. The advent of animal domestication and an agricultural diet may also resulted in an over-abundance of starch-based calories, which exceeded growth and energetic requirements [1].
The remainder of 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).
Looking at it from the perspective of man’s evolutionary history, the appearance of cereal grains is very recent. Cereal grains as food were non-existent in the evolutionary diet. Same with legumes, such as chickpeas and lentils. These too were non-existent in the evolutionary diet. Refined sugar (made up of sucrose) was also non-existent in the evolutionary diet. Humans would eat wild fruit (fructose) and on the rare occasion when available they would eat honey (half glucose, half fructose), but this idea of a diet centering around sucrose and fructose was simply non-existent.
Consumption of dairy products and alcohol are also very recent in terms of human history. We didn’t milk wild animals, we ate them. Fermentation of fruit for wine is also very recent in terms of the evolutionary diet.
Our body did not evolve to see cereal grain, legumes, refined sugar, dairy foods and alcohol and all of these are very rich in carbohydrate.
We are exposed to carbohydrate in a way that were never evolved to see.
Our bodies developed metabolism patterns around our dietary intake of protein and fat.
We have very extensive and elaborate pattern for handling protein; for digesting and metabolizing it. We also have developed a very high ‘satiety’ (feeling full) to protein, such that we simply won’t over eat it. It is the only macronutrient that provides sufficiently strong feedback such that we can’t over eat it.
Fat, contrary to common belief is a very passive nutrient. It has very little direct effect on our body. We store it effectively and this ability to store excess intake as fat is what enabled us to survive as hunter-gatherers.
The macronutrient that is at odds in this picture is carbohydrate.
We have very little evolutionary exposure to carbs; in fact the body responds to it has if it were highly toxic. Carbs have to be rapidly cleared after we eat it because our body must maintain our blood sugar within a very narrow range between 3.3-5.5 mmol/L (60-100 mg/dl). When we eat carbohydrate, the body breaks it down to simple sugar (glucose) and insulin takes the extra sugar out of the blood and moves it into cells. Our only mechanism to protect us from carbohydrate is insulin. The problem is, when we eat carbohydrates every few hours, the ability for insulin to respond becomes overwhelmed.
We have a biological system for handling carbohydrate and the traditional teaching is that carbs are handled in the muscle, which is true if one exercises 2-3 hours per day. When were were hunter-gatherers and we came across a bee hive, for instance or a fruit tree in season, our muscle was able to process the short spike in glucose load because we were very active. The average North American or European is not typically exercising that much, with ~75% considered sedentary (inactive).
So where are those carbs going?
They’re going to body fat.
Carbohydrate regulation is very important to think about. Carbs are among some of the most regulated substances in the body. Blood sugar is controlled and kept within an extremely tight range between 3.3-5.5 mmol/L (60-100 mg/dl).
If we don’t burn off the 30 gm of carbs (equivalent to ~ 6 tsp of sugar) we ate for breakfast by the time we have a fruit mid-morning (another 15 gm of carbs / equivalent to 3 tsp of sugar), we have to store the carbs somewhere. Comes lunch, most people eat another 30 – 45 gm of carbs (~6 – 9 tsp of sugar) if they’re eating a lunch brought from home and even more than that if eating out at the food court. Maybe another fruit is eaten mid-afternoon, and without realizing it, people have consumed the equivalent of 24 tsp of more of sugar, eating what they’ve believed is a healthy diet. As explained in a previous post, the blood can only have at most the equivalent of ~ 1 tsp of sugar in it at any one time, so where does all the sugar go?
It goes to fat stores.
Our body is constantly pulling out free fatty acids from our fat stores (adipose tissue) when we are sleeping or exercising, for example to use as a fuel source, so the free fatty acids that are coming in from adipose tissue (fat stores) and those that are being synthesized from glucose (the excess carbs we took in our diet) mix in the liver, and are then packaged into very-low-density lipoprotein (VLDL).
Think of these VLDL as ”taxis” that move cholesterol, triglycerides and other fats around the body. Once these VLDL “taxis” deliver their payload, the triglyceride is stripped out and absorbed into fat cells. The VLDLs shrink and becomes a new, smaller, lipoprotein, which is called Low Density Lipoprotein, or LDL — the so-called bad cholesterol’.
[Calling LDL ‘bad cholesterol’ is a misnomer, because not all LDL is harmful. LDL which is normally large and fluffy in texture is a good cholesterol (pattern A) that can become bad cholesterol (pattern B) when it becomes small and dense. In a healthy person, LDL is not a problem because they find their way back to the liver after having done their job of delivering the TG to cells needing energy. In a person with insulin resistance however ,the LDL linger a little longer than normal, and get smaller and denser, becoming what is known as ”small, dense LDL” and these are the ones that put us at a risk for cardiovascular disease.]
The origins of high triglycerides is the beginning of Metabolic Syndrome (also called Syndrome X). This is the point at which the body is getting too many carbs and the system is breaking down. The result is high than normal blood sugar after meals (called post prandial glucose), an increase in free fatty acids, and the increase in triglycerides and these together contribute to fatty liver. These are all symptoms Metabolic Syndrome.
If one is eating more than 30 gm of carbohydrates per day then they either need to have very high exercise to account for it, or they’re going to be making fat from it.
With an average carb intake of 300 gm per day and 75% of North Americans sedentary, it is easy to see where the problem of excess fat stores comes from.
Since our only mechanism for dealing with carbohydrate is insulin, by continually overwhelming the body with a steady supply of glucose – way above the small amount of carbohydrate that our genome has adapted to see, the system fails. This is where the origins of the overweight and obesity statistics elaborated on in the first part in this series (located here).
To address this carbohydrate excess, we can lower carbohydrate intake and either raise fat intake or raise protein intake. In Part III of this series, we will shift the focus to the benefits of increasing protein in the diet.
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References
- Luca F, Perry GH, Di Rienzo A. Evolutionary Adaptations to Dietary Changes. Annual review of nutrition. 2010;30:291-314. doi:10.1146/annurev-nutr-080508-141048.
- Goren-Inbar N, Alperson N, Kislev ME, Simchoni O, Melamed Y, et al. Evidence of hominin control of fire at Gesher Benot Ya’aqov, Israel. Science. 2004;304:725—727
- Brain CK, Sillent A. Evidence from the Swartkrans cave for the earliest use of fire. Nature. 1988;336:464—466.
- Evidence for the use of fire at zhoukoudian, china
Science. 1998 Jul 10; 281(5374):251-3.
- Copeland L, Blazek J, Salman H, Chiming Tang M. Form and functionality of starch. Food Hydrocolloids. 2009;23:1527—1534.