Is the Ketogenic Diet Natural for Humans?

As discussed in the first article of this series, ketosis is a metabolic state in which the brain switches to using ketone bodies – derived from the breakdown of fat – as its primary energy source, instead of glucose. Dietary Nature Keto This way body protein, which would otherwise be broken down and converted into glucose through the process of gluconeogenesis, are spared.

Dietary-Nature-Keto-940x534

Ketosis is an adaptive state that allowed our ancestors to survive temporary food shortages. When food was not available at all, or the only food available was extremely low in energy (such as leaves and grasses), their bodies could start to break down their body fat reserves after a couple of days. Ketone bodies were generated as a result allowing them to sustain their brains and preserve their muscle and other vital proteins.

Our human ancestors did not consume high-fat, low-carbohydrate diets and therefore would not have been in diet-induced ketosis.

Note the emphasis on ketosis as a temporary adaptive state. Our ancestors could not be in fasting-induced ketosis permanently because they would eventually exhaust their fat reserves (which were presumably far more limited than ours, owing to the simple fact that they ate less and moved more than we do). They would then progress from fasting to starving, and subsequently die.

Yet ketogenic diet proponents advocate that we should aim to keep ourselves in a permanent state of ketosis, something that is completely foreign to human experience – and to the experience of all other animals, for that matter.

Ketosis in Non-Human Animals

No animal on earth lives permanently in ketosis. Omnivorous animals such as bears and dogs, and obligate carnivores such as cats – the ultimate low-carbers – use gluconeogenesis to transform amino acids from protein into glucose[1]. This allows them to maintain optimal blood glucose levels to fulfill their bodies’ needs for this vital nutrient. Only in prolonged starvation or a diabetic state will these animals enter ketosis.

Even hibernating bears do not go into ketosis[2]. And predatory animals who undergo extended periods of food deprivation, such as elephant seals[3], are metabolically resistant to ketosis; instead, they have upregulated gluconeogenesis pathways through which they can steadily produce glucose. This makes perfect sense, since predators’ survival depends on their ability to catch their prey, which usually requires intense bursts of activity. And sprinting capacity is dependent on glucose, as humans who adopt a ketogenic diet quickly discover.

Even when exercising at a submaximal level (for example, biking at a moderate speed), heart rate and adrenaline levels rise more when people are eating a high-fat, low-carbohydrate diet[4] vs. a high-carbohydrate, low-fat diet. This results in those on the high fat diet perceiving that they are working harder to achieve the same pace as the high-carbers, and they have much more difficulty speeding up their pace in sprints or climbs.

Even in endurance sports that don’t require sprinting, ketogenic-style diets are disadvantageous according to a ketogenic diet and exercise article published in Sports Medicine[5]: “a high-fat, low-carbohydrate ketogenic diet may impair exercise performance via reducing the capacity to utilize carbohydrates, which forms a key fuel source for skeletal muscle during intense endurance-type exercise.” The article concluded, “At present there are no data available to suggest that ingestion of ketone bodies during exercise improves athletes’ performance under conditions where evidence-based nutritional strategies are applied appropriately.”

Ketosis in Early Humans

Our human ancestors did not consume high-fat, low-carbohydrate diets and therefore would not have been in diet-induced ketosis. Even the most successful early hunters could not possibly have consumed enough fat to enter ketosis since african wildlife such as wildebeests, warthogs and impalas all have low body fat – well under 10%, and as low as 0.3%[6] in the dry season.

Furthermore, humans develop a condition dubbed ‘rabbit starvation’[7] when they eat a diet that is low in fat and carbohydrates, and high in protein (> 35% of total daily energy intake). This is due to the inability of the human liver to sufficiently upregulate urea synthesis to meet excessive loads of protein. Consequently, hyperaminoacidemia, hyperammonemia, hyperinsulinemia, nausea, diarrhea, and even death can ensue within 2 to 3 weeks. These effects were recognized historically through the excess consumption of lean wild meat by early American explorers.[8]

“But What About the Inuit?”

The Inuit (Eskimo) peoples inhabiting the Arctic regions of Greenland, Canada and Alaska are frequently cited by ketogenic diet advocates as an example of a human population adapted to eating a high fat, low carbohydrate and relatively low protein diet. Here’s a typical example:

What is the Ketogenic Diet?

The Eskimos and Maasai group are cultures we often look at to learn how their scant consumption of carbohydrates sustained their bodies through harsh weather conditions. It turns out their low carb diet switched their metabolism to burn fat instead of sugar or glucose.

This created a metabolic state known as ketosis, a process in which the body burns ketones to make energy, instead of relying on sugar or carbohydrate.

Yet as far back as 1928, researchers conducted experiments on Inuit people who were still eating their traditional diet[10] comprised on average of 280 g of protein, 135 g of fat, and 54 g of carbohydrate per day ( the latter derived primarily from muscle glycogen found in raw meat) which established two important facts:

  1. Inuit people were not in ketosis on their regular diet; instead, their high protein intake resulted in gluconeogenesis – just like carnivores and omnivores.
  2. Even in the fasting state, Inuit people showed resistance to entering ketosis. The researchers observed that “On fasting he develops a ketosis, but only of mild degree compared to that observed with other human subjects.”

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