Going Hybrid Makes Evolutionary Sense

Dual Fuel

Why did we become hybrid, with the ability to both burn glucose from carbs and ketones from fat? Why did evolution decide that we needed to derive energy from both glucose and ketones? Some animals can’t do this at all, but we are extremely good at it. In addition, human babies run on ketones from the moment they are born until several months after they finish breastfeeding. What benefits do they derive from meeting their energy requirements in this way?

All species survive because they thrive on a particular diet and develop a set of characteristics and skills that allow them to establish themselves in a specific environment. Clues to our ideal diet and environment can be found in the human brain. It’s not just the brain’s size but its complexity and highly developed frontal cortex that set us apart from other species. Infants make a staggering one million new neural connections every second1, and their brains burn through 75 per cent of the energy they use.

To fuel this furious growth, they need to top up their supplies of glucose from the moment they arrive in the world. They get this extra energy from ketones, which they make from breast milk and their own reserves of fat. By contrast, less intelligent mammals, such as bears, turn their stored fat into a form of glucose (glycerol) during hibernation. Their smaller brains have lower energy demands, so they don’t need to bother with ketones. Meanwhile, the larger brains of dolphins and seals are similar to our own. Indeed, they prefer to run on ketones, rather than glucose, if the former are available.

We didn’t survive on the savannah because we started to stand upright and throw spears. Our muscles are, frankly, puny compared to those of other animals. And even lions, whose bulging muscles, strength and speed are far superior to ours, don’t have a particularly good strike rate during hunts. Therefore, we needed to increase our chances of securing a meal through intelligence, not muscle power. Key to this was our ability to convert omega-3 into DHA, one of the main building blocks of all mammalian brains.

Unfortunately, though, while the lean meat of savannah animals was a good source of many nutrients, it contained little or no omega-3, so we needed to top up our supply with nuts and seeds. Consequently, we evolved to survive on a largely vegetarian diet and usually burned glucose for energy. However, we also developed sufficient brain power to become fairly efficient hunters of much larger, faster and stronger animals, which gave us access to occasional supplies of protein and fat. In those times of plenty, our consumption of carbs decreased and we started to hone our ability to run on ketones.

This early version of the dual fuel system gave us a much better chance of survival if either food source ran out, but it was still far from the finished article. We needed a much richer source of omega-3 – along with selenium and iodine – if our brains were ever to grow into the super-computers that they are today. That meant we had to make our way to the seaside.

Homo Aquaticus

Genetically, we are quite close cousins of chimpanzees. Our family trees diverged a mere seven million years ago, and we share 98.5 per cent of the same genes. Yet, in other respects, we are utterly different. So, how did this happen? The answer is that we spent a lot of time in – or next to – the water, while chimpanzees did not.

We all have a layer of subcutaneous fat: human babies, unlike all other land mammals, are born with lots of it. In addition, we have a larger brain to body weight ratio and a much higher concentration of omega-3 fatty acids (such as DHA) in our brains than any other mammal as well as an ability to convert fat into ketones rapidly. Moreover, as we saw earlier, we continue to use ketones for brain fuel long after weaning. We also have a remarkable ‘swimming reflex’. Babies will happily dive into the water, hold their breath while they are below the surface, then start breathing again when they pop back up. While underwater, they stay calm, open their eyes and even know how to roll over onto their backs without the water going up their noses. And we are all born with a coating of vernix – a waxy, waterproof layer. No other land mammals have this.

All of this, coupled with the fact that we walk upright, on two legs, gave us a unique evolutionary advantage to thrive in a specific environment. ‘The niche that ultimately made us human was coastal areas, rivers and wetlands – the water’s edge,’ says Professor Michael Crawford, Director of the Institute of Brain Chemistry and Human Nutrition and a champion of the ‘Homo aquaticus’ theory, which is supported by an ever-increasing body of evidence. The argument is that our ancestors left the jungles and savannahs of central Africa and made their way to the water’s edge, most likely the stretch of coastline that now runs from Eritrea in the north-east of the continent to South Africa. This coast was – and still is – fringed by reefs that hold an abundance of seafood.

Crawford suggests that our ancestors simply waded into the shallow water and helped themselves to the mussels, oysters, crustaceans and fish, which provided the copious supplies of omega-3s and other critical nutrients that allowed our brains to grow to unprecedented size. Neither a vegetarian nor a meat-based diet provides these nutrients in anything like the same quantities, so it is highly unlikely that the human brain would have developed as it did if our ancestors had not made that decisive move to the coast. In addition, their diet would have been much lower in carbs and higher in fat and protein than those of earlier generations, which would have had the effect of increasing their reliance on ketones.

The migration to the coast occurred about two million years ago, according to the fossil record. Thereafter, there was a steady growth in brain size from 450g to 1,490g, which Homo sapiens achieved about 100,000 years ago. Meanwhile, these early humans also evolved a much more upright posture than their savannah-dwelling ancestors (and indeed the chimps that remained there). The evolutionary advantages of this upright stance are obvious, given where they were living and what they were eating: it allowed them to wade further into the coastal lagoons for the richest pickings.

About 1.8 million years ago, after a few hundred thousand years of rapid mental and physical development on the East African coast, Homo erectus started to explore further afield. They reached the southern Mediterranean, the Middle East, India and East Asia. By then, the human brain had already doubled in size to 940g. Later, those who remained in – or possibly returned to – Africa ultimately evolved into Homo sapiens. Then, like their ancestors before them, they started to spread around the world, too. Recent archaeological discoveries in China, Israel and Morocco suggest that our species reached these places around 180,000 years ago.2

The most ancient rock art – which has been dated to around 80,000 BCE – is in sub-Saharan Africa, which had a vast network of lakes, rivers and wetlands at the time. One particularly significant cave painting from this period shows a group of early humans swimming. Then weather patterns changed, the monsoon moved further south, and the whole area dried up. By 10,000 years ago, only the Nile was left. Further north, the Tigris and Euphrates (in modern-day Iraq) were similarly isolated water sources. It was along the banks of these rivers that human civilisation and culture started to flourish, and even today the vast majority of the world’s major cities are on the water’s edge.

Having identified our close connection with coasts and rivers throughout our evolutionary history, Michael Crawford laments the decline in omega-3 in our diet. Indeed, as early as 1972, he argued that we will become a race of morons if we continue to eat the modern Western diet. He warned of an ever-increasing incidence of mental illness, lower IQs and more children with ADHD, autism and other serious disorders. So, has this dire prediction come true? Well, mental illness is now the number-one global health issue and one recent study found that average IQ has fallen by seven points in a single generation.3

Babies Run on Ketones

Clearly, then, our ancestors’ adaptation to a diet that included marine fats and extra protein – and their reduced reliance on carbs – was the key development that enabled our brains to grow much larger than those of other primates. An integral part of this process was that we honed our ability to run on ketones, because we needed to ensure that our expanding brains never ran out of fuel.

According to Professor Stephen Cunnane from the University of Sherbrook in Quebec, ‘Ketones are the back-up fuel to glucose in the human adult, but in the neonate [infant] they are the predominant brain fuel.’ While other large-brained animals have some capacity to convert fat into ketones, we are far better at it, and our babies – more than the offspring of any other land mammals – actually depend on them.

Campfires on the Beach

However, it wasn’t just the oils and proteins in seafood that shaped our development. Another significant milestone was the discovery of fire about 1.8 million years ago. Thereafter, and especially after around 500,000 BCE, cooking had a huge impact on our ancestors’ diet and evolution. It made previously hard to digest root vegetables and beans more edible and therefore valuable new sources of energy because of the low GL carbs they contain.

This coincided with the ongoing steady increase in brain size, along with a parallel increase in aerobic capacity, a shortening of the gut and a reduction in tooth size. A plausible explanation for all of these physiological changes is that cooking meant our ancestors needed to spend less time chewing food in the mouth as well as digesting and absorbing nutrients in the gut. Uncooked vegetables, meat and fish all demand a lot of chewing.

Our genes support this theory. About a million years ago, multiple variations in carbohydrate-digesting amylase enzymes – which turn cooked starch into glucose – started to appear. This meant that more fuel was available for both the body and the brain. ‘Consumption of increased amounts of starch may have provided a substantial evolutionary advantage to Mid-to-Late Pleistocene omnivorous hominins,’ according to Karen Hardy and Jenny Brand-Miller from the University of Sydney4. Cooked starch – a rich source of preformed glucose – greatly increased energy availability to human tissues with high glucose demands, including the brain, red blood cells and developing foetuses.

By 20,000 BCE, the hunter-gatherer Homo sapiens’ diet consisted chiefly of lean meat, fish and shellfish, eggs, vegetables and fruit. Some wild lentils, grasses, grains and peas may have been eaten too, but these foodstuffs didn’t take off in a major way until the Agricultural Revolution, more than 10,000 years later. There was no consumption of dairy products, and of course no processed food.

The New Foods

Everything changed with the Agricultural Revolution when man, due to climate change, was forced to grow food (I explain how this happens in the Hybrid Diet book). The principal products of the Agricultural Revolution – wheat and milk – now account for a third of the calories in a typical Western diet.

The Mesopotamians domesticated goats, whose milk and especially cheese are very high in butyric acid, a healthy pre-ketone that is good for the gut. Industrially produced cow’s milk is rather different. Genetically, there are two different kinds of cow’s milk – A1 and A2. Today, we mainly drink A1, which is produced by cows with the highest milk yields. Nile Basin cows, yaks and Jersey cows all produce smaller amounts of A2. Yet, A1 generates digestive discomfort in a much larger proportion of the population as well as inflammation in both lactose tolerant and intolerant individuals. In other words, we seem to be less well adapted to drink A1 milk.5

Meanwhile, the earliest wheats – khorasan (also known as Kamut bulgur), emmer and durum – are genetically much simpler than modern wheat. They are known as tetraploid grains because they have just four sets of chromosomes, whereas modern wheat and spelt have six sets. More than twenty studies have found that modern wheat promotes inflammation whereas Kamut bulgur does not6. For example, in a recent trial involving participants with non-alcoholic fatty liver disease – which is often found in diabetics – those eating Kamut bulgur not only improved their liver function but also halved their level of inflammation7. Similarly, eating modern wheat tends to exacerbate the symptoms of IBS8, whereas most sufferers are able to tolerate Kamut bulgur, even though it contains gluten.9

An estimated one in thirty people with digestive problems have coeliac disease – a severe intolerance to gluten – whereas approximately one in five are gluten-sensitive but not coeliacs. It is not known whether the prevalence of these ailments is due to the differences between modern and ancient wheats, the high proportion of gluten in the Western diet, or a combination of the two. However, natural selection probably meant that those people who could not tolerate wheat of any kind died out in the Middle East between 10,000 and 2,000 years ago, leaving behind a population who could eat it quite happily. By contrast, wheat was unknown in the Northern European diet in that period, so no such natural selection took place. This may explain why gluten intolerance is such a problem in Northern Europe and other Western countries – but not in the Middle East – today.

Similarly, nomadic herdsmen in Africa suffer little of the lactose intolerance that blights the lives of so many Westerners. Their ancestors were among the first humans to start herding cattle, so those who were able to digest milk efficiently enjoyed a huge evolutionary advantage over the rest. Consequently, over time, these tribes became characterised by their tolerance for dairy products. Cattle herders in Europe and the Middle East evolved in a similar way. By contrast, societies with no ancient tradition of cattle rearing – such as the Chinese, Thai, Pima Indians of the American Southwest and the Bantu of West Africa – all have very high rates of lactose intolerance.

Paleo, Vegan and Ketogenic Diets

The so-called ‘paleo’ diet is full of whole foods – vegetables, fruit, nuts, seeds, eggs, fish and ‘healthy’ lean meat. It shuns grains, beans and dairy products on the basis that these are all recent interlopers in humankind’s evolutionary history. (Although some paleo people make an exception for peas, which are members of the bean family, because there is evidence that our close cousins, the Neanderthals, ate them at least 46,000 years ago.) It is also quite meat oriented, as are most ketogenic diets, although it has no particular problem with fish. The standard Atkins diet is especially high in meat and dairy products.

Vegans avoid all meat, eggs, fish and dairy products. The decision to adopt such a radical diet is entirely understandable ethically, given the terrible ways in which animals are reared, treated and slaughtered; environmentally, as it is more economical to grow a field of beans than feed a herd of cows; and politically, as it cocks a snook at the unscrupulous food manufacturers that are more interested in boosting their profits than safeguarding their customers’ health. As Michael Crawford says, ‘If you eat obese animals, you’re going to get obese. In today’s animals, there are six times more calories from fat than protein. The balance of nutrients is all wrong. Chicken are sold without the skin – which is rich in fat, flavour and nutrients – because more money can be made elsewhere, selling the skin, which is processed to add flavour to manufactured foods.’ Many vegans and vegetarians adopt their diets because they are appalled by these gross perversions of factory meat farming and the dairy industry.

Unfortunately, though, for all their merits, there are some significant problems with vegan diets, especially for those who switch without any knowledge of nutrition. For instance, vegans find it particularly difficult to get enough vitamin B12 (which is non-existent in the vegetable kingdom), DHA (the key omega-3 fat, which is essential for brain development), vitamin D (which is found in high concentrations in fish) and selenium (which is also rich in seafood). The highly respected Avon Longitudinal Study found that the children of vegans – and others who eat little seafood – have below average cognition and social development10, while their mothers suffer from more anxiety during pregnancy11. The human body simply cannot convert flax seeds into sufficient quantities of DHA to facilitate optimal foetal brain development. Therefore, in my opinion, it is essential for vegans to supplement either omega-3 fish oils or DHA derived from seaweed throughout pregnancy and breastfeeding. Similarly, eggs are among the best sources of phospholipids, which are also vital in brain development.

Fans of paleo diets often highlight the advantages of eating grass-fed cattle rather than intensively reared, carb-fed cows. However, while beef from animals fed on high carb corn is certainly more marbled, fattier and therefore less healthy than the grass-fed alternative, even the latter is not truly paleo, if the intention is to replicate the diets of our hunter-gatherer forebears. It was much later in our evolutionary journey that a few tribes had the idea of keeping hoofed animals in a pen and forcing them to eat grass. In addition to being genetically very different from all modern cows – organically reared and grass-fed or otherwise – these animals were forest-dwellers and their natural diet consisted of hedges and bushes. A prehistoric hunter-gatherer might spear or snare one of these lean, wild beasts every once in a while, but his daily diet would consist primarily of fish, shellfish and plants.

Many ketogenic advocates insist that, while protein and fat are essential food groups, carbohydrates are not. However, there is a flaw in this argument because it is impossible to consume sufficient quantities of many nutrients – including antioxidants and polyphenols – if you swear off all carbs for good. Indeed, it is much more accurate to say that dairy products are not an essential food group. Moreover, they had no place in 99 per cent of our evolutionary history, so it is hardly surprising that half of the world’s population are lactose intolerant. Yet, countless ketogenic enthusiasts make dairy an integral part of their diet.

Whether you are a fan of ketogenic, paleo, low carb or low GL, the chances are that you have a burning desire to eat unadulterated wholefoods, rather than junk food or the meat of intensively reared animals. In addition, though, many studies have found that eating any red meat – irrespective of how the animal was reared – increases the risk of developing various cancers, diabetes and heart disease. Crucially, there is no corresponding risk from eating fish. Indeed, in general, the more fish and vegetables you eat, the lower your risk of contracting any of these illnesses. So, it might be time to bypass the butcher’s and make your way to the fishmonger’s instead.

Why Our Dual Fuel System Gave Us an Evolutionary Advantage

Throughout the course of human evolution, we have benefited from our ability to run on two fuels – glucose and ketones – for the following reasons:

  • The metabolism of ketones has been critical for human infants’ brain development.
  • Our ancestors we able to survive in different times and places, despite the varying availability of plant and animal-based food.
  • Our diverse diet gave us access to a wide variety of nutrients that were not available to other animals, which facilitated the unprecedented growth of the human brain. However, many of these nutrients do not feature in modern diets, so were are in danger of devolving, rather than evolving, if we continue down the same path. Indeed, this may happen much faster than most evolutionary processes. One recent study found that diabetics’ genes are altered by the condition, so they may pass on susceptibility to the disease to the next generation.12
  • We have not evolved to survive exclusively on plant-based food, which is why vegans should supplement key nutrients such as B12 and DHA. Fish and shellfish have long been important sources of brain-friendly nutrients and indeed may have been the key food group that made us human.
  • We did not rely on a very narrow diet, such as one that was heavily reliant on grains and dairy products. Consequently, it is not a good idea to limit our options in this way today.
  • Our ancestors ate a little unprocessed, lean meat but got most of their protein from seafood, which is packed with omega-3s that aid brain development. Today, many people eat too much (and much less healthy) meat, while consumption of fish and shellfish has fallen dramatically. We need to reverse this.

Therefore, from an evolutionary perspective, the hybrid approach – which derives energy from both low GL carbs and fat while conserving protein for essential growth and repair – makes perfect sense. In addition, there may be health advantages from replicating the vast majority of our evolutionary history by fasting and/or initiating ketogenesis from time to time.

Variety – in terms of eating a wide range of foods and switching between ketones and glucose for fuel – may indeed be the spice of a healthier life.

Extracted from The Hybrid Diet.

Published by Little Brown.

The Hybrid Diet is available from HOLFORdirect from 21 March.

About the TOUR

If you’d like to find out more I will be touring the UK and Ireland in March/April. Seminars will be held in:

Daventry; Manchester; Dublin; Belfast; Sligo; Galway; Tralee; Cork; Kilkenny; Cardiff; Marlow; Richmond; London (South West); London (Central, Piccadilly); London (East, Clerkenwell) and there will be a talk at the Natural Products Show – Trade only (London, Excel)

To book, go to www.patrickholford.com/events



1. Center on the Developing Child, Five Numbers to Remember about Early Childhood Development, http://www.developingchild.harvard.edu.

2. K. Douglas, ‘Asia’s mysterious role in the early origins of humanity’,

3. B. Bratsberg and O. Rogeberg, ‘Flynn effect and its reversal are both environmentally caused’, Proceedings of the National Academy of Sciences (2018),

4. K. Hardy et al., ‘The importance of dietary carbohydrate in human evolution’, Quarterly Review of Biology (2015), vol 90(3):251–268.

5. S. Jianqin et al., ‘Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk’, Nutrition Journal (2016), vol 35:45.

6. See https://www.patrickholford.com/advice/kamut-khorasan-wheat-supergrain.

7. J.R Hibbeln et al., ‘Healthy intakes of n3 and n6 fatty acids: estimations considering worldwide diversity’ Am J Clin Nutr 2006; 83(suppl):1483S–93S.

8. J. Hollon et al., ‘Effect of gliadin on permeability of intestinal biopsy explants from celiac disease patients and patients with non-celiac gluten sensitivity’, Nutrients (2015), vol 7(3):1565–1576; see also J. Biesiekierski et al., ‘Gluten causes gastrointestinal symptoms in subjects without celiac disease: a double-blind randomised placebo-controlled trial’, American Journal of Gastroenterology, vol 106(3):508–514.

9. F. Sofi et al., ‘Effect of Triticum turgidum subsp. turanicum wheat on irritable bowel syndrome: a double-blinded randomised dietary intervention trial’, British Journal of Nutrition (2014), vol 111(11):1992–1999.

10. J.R. Hibbeln et al., ‘Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): an observational cohort study’, Lancet (2007), vol 369(9561):578–585.

11. S. Vaz Jdos et al., ‘Dietary patterns, n-3 fatty acids intake from seafood and high levels of anxiety symptoms during pregnancy: findings from the Avon Longitudinal Study of Parents and Children’, PLoS One (2013), vol 8(7):e67671.

12. Y. Wei et al., ‘Paternally induced transgenerational inheritance of susceptibility to diabetes in mammals’, Proceedings of the National Academy of Sciences of the USA (2014), vol 111(5):1873–1878.