In part 1 of this series on carbohydrate intake we looked at what our biology and physiology tell us about adaptation to diet and established what types of foods that fueled the evolution of our large brains. Although we do have some knowledge about the diet of early hominins, there’s clearly a lot of uncertainty as to what our very ancient ancestors actually were eating. As we move closer and closer towards contemporary times, the data on nutrition and human health get more comprehensive and detailed. In this second part we’ll begin where we left off in part 1, with the emergence of anatomically modern humans about 200.000 years ago.
What can the diets of the healthiest populations that have ever been studied tell us about optimal carbohydrate intake?
– Ancestral diets
If we go way back in history, all humans descend from predominantly plant-eating primates, but as we know, it’s not really that relevant what our very early ancestors ate. What we want to look at is our genus, Homo, and especially our species, Homo sapiens sapiens.
Amount of carbohydrate in ancestral diets
If we are to believe the fossil record, the first anatomically modern humans (AMHs) were living in East Africa about 200.000 years ago – a location they stayed in up until about 70.000 years before present. What did the diet of these first AMHs look like? To assume that the paleolithic diets of our African ancestors didn’t change much up until the agricultural revolution would clearly be a simplification. However, as we know, there are some overarching trends.
The best available estimates suggest that those ancestors [behaviourally-modern humans in East Africa 100-50 x 10(3) years ago] obtained about 35% of their dietary energy from fats, 35% from carbohydrates and 30% from protein” (1).
Other ratios than the one above have been proposed, and there’s no doubt that macronutrient intake would have varied significantly between the seasons, but in my opinion, these numbers represent a good plausible average estimation.
What about the data we have on worldwide hunter-gatherers and other populations eating ancestral diets? In terms of carbohydrate intake, we know that the average intake varied/varies greatly between different healthy, non-westernized populations, and while some non-modernized cultures, such as the Tukisenta highland tribe, seemed to do well on a diet that contained as much as 94% carbohydrate, other populations, such as the Inuit, get the vast majority of their energy from fat and protein. Subsistence data from 229 hunter-gatherer diets suggest a plausible percentage of carbohydrate of 22-40% of daily calories; meaning that in general, ancestral diets are lower in carbohydrate than the diet recommended by official health authorities today (2). Although these numbers have later been questioned by other researchers (3), there’s wide agreement that the range of energy intake from carbohydrates in the diets of most hunter-gatherer societies – both modern populations and paleolithic tribes – was markedly different (lower) than the amounts currently recommended for healthy humans (2,4,5,6).
It’s only natural that ancestral diets tend to be lower in carbohydrate than modern diets, as hunter-gatherers eat little or no cereal grains and consume high amounts of animal source food when possible. However, as I’ve already pointed out, the notion that ancestral diets are always high in fat and low in carbohydrate has little support in the literature. Nuts, tubers, and fruits were important staple foods in many hunter-gatherer tribes, wild game tends to be leaner than the domesticated animals today, and contrary to what some people seem to believe, hunting is difficult and often unsuccessful.
Bottom line: The amount of carbohydrate in hunter-gatherer diets depends on the ecoenvironment. Hunter-gatherers living in desert and tropical grasslands tend to consume more carbohydrates than hunter-gatherers living in northern areas (tundra and northern coniferous forest). Ancestral diets are pretty much always lower in carbohydrate (usually within the 10-40% range) than the amounts recommended by official health authorities today (45-65%).
A transition from eating “ancestral food” to eating modern food
Okay, so in general, ancestral diets are clearly low-carb compared to modern standards. But let’s dig a little deeper and look at how the foods that make up the carbohydrate portion of hunter-gatherer diets differ from the high-carb foods consumed in westernized countries today. Because this is really where a lot of the clues lie. Carbohydrates aren’t problematic per se, but many of the high-carb foods we eat in today’s society definitely are.
Increasing carbohydrate density
For hunter-gatherers, nuts, fruits, and/or tubers tend to provide the majority of carbohydrates in the diet, while in today’s society, these foods have to a large extent been replaced by cereal grains, milk, sugary beverages, and highly processed food items. The differences between these food groups are huge. One of the most obvious ones being that “ancestral sources” of carbohydrate have a markedly lower carbohydrate density than grains and sugar-filled modern products. Here’s a quote from Ian Spreadbury’s excellent review paper on acellular carbohydrates:
Tubers, fruits, or functional plant parts such as leaves and stems store their carbohydrates in organelles as part of fiber-walled living cells. These are thought to remain largely intact during cooking, which instead mostly breaks cell-to-cell adhesion. This cellular storage appears to mandate a maximum density of around 23% non-fibrous carbohydrate by mass, the bulk of the cellular weight being made up of water. The acellular carbohydrates of flour, sugar and processed plant-starch products are considerably more dense. Grains themselves are also highly dense, dry stores of starch designed for rapid macroscopic enzymic mobilization during germination (7).
This comes back to something I’ve talked a lot about on the blog: The transition from eating foods with an “ancestral nutrient composition” to eating foods with a more “unnatural” nutrient composition. Even foods that are often considered healthy, such as whole grains and dense sources of fat (e.g., oils), are very different from the foods consumed by our ancient ancestors. In itself, this isn’t necessarily a problem, but as we know, the evolutionary template gives us a good idea of what we should eat to achieve optimal health. Studies show that both very dense sources of fat and dense sources of carbohydrates can initiate processes that lead to low-grade chronic inflammation.
And it’s not just that we’ve introduced new foods that were not a part of the ancestral diet; even the food groups that we have access to at the supermarket which are supposedly “paleo” tend to be very different from those consumed by hominins for millions of years. A good example of this is fruit; which we today tend to associate with something very sweet, while in the wild, fruit tends to be more sour.
Decreasing micronutrient and fiber content
Besides the elevated carbohydrate density, we know that the plant foods available to us today tend to have a poor micronutrient profile compared to those consumed by our ancient ancestors, and perhaps more importantly, they tend to have a very different content of dietary fiber (8,9). Uncultivated vegetables and fruits can be markedly more fibrous (13.3 g fiber/100 g) than commercial ones (4.2 g/100 g) and they also have a much lower starch content. In other words, a cooked potato from the grocery store will affect your insulin secretion and microbiota differently than a wild tuber.
Loss of old friends
Besides the transition from eating very nutrient-dense foods with a relatively modest concentration of carbohydrate, to eating less nutrient-dense foods with a high concentration of carbohydrate, there is one other important change I want to discuss. Namely that we’ve gone from eating “dirty” food to eating “clean” (often heated) food. When living as a hunter-gatherer, it’s almost impossible to avoid coming in contact with millions of soil microbes on a daily basis from untreated water, food with clinging soil, and the rest of the natural environment. Clearly, there are certain safety concerns associated with this type of behaviour – but overall, the data suggest that this high exposure to microorganisms could be one of the key reasons hunter-gatherers are so healthy.
These soil microbes have co-evolved with us for millions of years, and they help stimulate our immune system and aid in the digestion of plant polysaccharides. It’s only recently – on an evolutionary timescale – that we’ve “cut off” this contact with the natural environment by moving into large apartment buildings and double-washing our food. We’ve also changed how we produce food and altered the soil microbiome with pesticides and herbicides, meaning that the soil clinging to a tuberous root which has just been dug up by a member of the Hadza tribe can be very different from the “dirt” that cover conventionally produced plant foods today.
The fact that many of us tend to thoroughly heat (e.g., cook, fry) most of the plant foods we eat, not only decreases microbial exposure, but it can also decrease the amount of resistant starch and increase the glycemic load of our food. Hunter-gatherers often roast, cook, or in some other way heat their food, but they tend to consume a large portion of their plant foods raw as well.
All of this is not to say that we should completely avoid oils and whole grains, not eat fruits, or never wash or cook our food, it just highlights the difference between the foods we eat today and those consumed throughout most of our evolutionary history. By returning to an ancestral dietary template and choosing high-quality, organic produce we can circumvent many of these problems.
Bottom line: Sources of carbohydrate in ancestral and modern diets are very different; a change that includes increased carbohydrate density, elevated glycemic index, lower microbial residue, and altered preparation methods.
– Traditional diets
Starch heavy diets introduced with the agricultural revolution were less nutritious than the ancestral diets consumed by our paleolithic ancestors. However, as we know, there are several populations who’ve maintained very good health on diets “high” in grains, dairy, and/or legumes, and in my mind, the non-westernized cultures studied by researchers such as Dr. Weston A. Price provide a good indication of how the healthiest grain- and dairy-eating cultures lived.
What about traditional mediterranean diets? These diets are certainly healthier than what most people eat today, but as I don’t think they are quite up there with ancestral, hunter-gatherer type diets and traditional diets, I won’t get into them here.
Amount of carbohydrate in traditional diets
There are clearly examples of populations out there who’ve done well on high carbohydrate diets – such as the Okinawans in Japan and some of the cultures studied by Dr. Weston A. Price – but even most traditional diets tend to be lower in carbohydrate than western diets consumed today. The reasons for this being that non-modernized people cherished fatty foods, such as organ meats and high-fat dairy, often fermented fruits and grains (which reduces the carbohydrate content), and consumed high amounts of animal products when possible. Also, it’s important to note that even though there are some examples of non-westernized cultures and hunter-gatherer populations who seem to do well on diets with either a very low or very high carbohydrate level, that doesn’t mean that these “extreme” diets are optimal.
Bottom line: Traditional diets are on average higher in carbohydrate than ancestral diets, but often on the low side compared to today’s standards.
A transition from eating traditional food to eating modern food
New processing techniques and decreasing food quality
Isolated traditional cultures usually put far more emphasis on correct preparation of cereal grains, seeds, and nuts – using techniques such as soaking, sprouting, and fermentation. This not only makes the food easier to digest and more micronutrient-dense, but it often tends to decrease the carbohydrate density as well. This is especially true for fermentation, which was also used to store fruits and vegetables for long periods of time.
The interesting thing about these traditional processing techniques is that they turn non-ancestral foods such as cereal grains and dairy, into foods that are more similar to the types of foods consumed by our prehistoric ancestors. Besides the fact that we’ve now largely abandoned these traditional processing techniques, the carbohydrate-rich foods consumed in these cultures were often very different from those we eat today (e.g., oat and barley have been replaced with wheat).
Bottom line: The introduction of cereal grains in the human diet with the agricultural revolution lead to the dilution of fat and protein in favor of carbohydrate. As we know, the transition from a hunter-gatherer existence to a farming existence is associated with a decline in human health. However, several isolated, non-modernized cultures have maintained “good” health on diets high in grains, legumes, and/or dairy; the “secret” being that they traditionally prepare their food, live a healthy lifestyle, and eat whole foods of extremely high quality.
If we look at how the healthiest populations that have ever been studied eat/ate, it quickly becomes clear that humans can maintain good health on diets differing widely in their macronutrient composition. However, on average, ancestral diets (often also traditional diets) are markedly lower in carbohydrate than what we consider “normal” today. Today, official dietary guidelines dictate that we should get 45-65% of our daily energy from carbohydrate, and grain-based diets are the norm in most parts of the world. This has led to the notion that a carbohydrate intake of ~55% is normal for our species, while a diet that contains between 15 and 40% carbohydrate is a low-carb diet. However, if we broaden our perspective and look at the evolution of our species as a whole, a carbohydrate percentage of 15-40% could be considered an average intake, while a diet that contains 45-65% carbohydrate is a high-carbohydrate diet.
Although the stereotypical image of a stone ager gorging on fatty meats every day doesn’t really reflect how most hunter-gatherers eat/ate, there’s no doubt that paleolithic humans were far better at burning fat for energy than the modern, starch-eating westerner.
In itself, all of this doesn’t mean that we should eat the same amount of carbohydrate as hunter-gatherers or other healthy, non-modernized cultures. However, these observations and studies give us a good indication of how a healthy diet looks like, and as is pretty much always the case, the evolutionary template is right on the mark. A carbohydrate intake that is markedly lower (but not too low) than the amount typically consumed in the western world today is well in line with what you get from a well-balanced diet that contains both high quality animal source food and plant foods.