As Homo sapiens have evolved over time, their diet has evolved with them. From the hunter-gatherer age to the development of agriculture to the modern era, the human diet and the methods used to acquire food have completely changed. With the industrial revolution, access to food became markedly easier due to the low cost of transportation and many of the food products that can be found in our local grocery stores today are from a different part of the world. Although it may seem like this increased reach has increased the variety in our diet, the truth is, our modern diet is composed of a limited range of domesticated vegetables, grains and animals. Additionally, the modern North American diet includes a lot of processed goods, which are high in salt, sugar, and fat. This diet, in combination with our sedentary lifestyle, contributes to many chronic diseases. Here, we take a look at the history of the Homo sapiens diet and examine why we have evolved to prefer foods that are high in fat, salt, and sugar.

4.4 Million Years
Around 4.4 million years ago, human ancestors migrated from a forested habitat to a more open environment. Fossil evidence from Australopithecus afarensis (a hominin that is closely related to the genus Homo) helped scientists reconstruct their diet. Anthropologists speculate that our ancestors had a fairly diverse diet with a mixture of vegetables and fruits, rather than any specific type of food.

4.1-1.4 Million Years
Between 4.1-1.4 million years ago, different hominin groups migrated to different environments (e.g., grassland, forest, and coastline) with different plants and animals. Around 2.6 million years ago, hominin also learned to use stone tools to process foods that were hard to consume, such as roots and stems. This was evidenced by the large and thickened enamel found on the teeth of early hominin fossils.

800,000 Years
Current evidence suggests that humans began to utilize fire around 800,000 years ago. It was concluded that by this time, our ancestors could use fire to prepare their food, which made meat and roots easier to consume. This was evidenced by the reduced tooth size observed in Homo erectus. Using tools and fire to process their food also improved the quality of their diet, which led to an increase in brain size and a decrease in gut size. In spite of these changes, there was still a diverse range of food consumed with low meat consumption.

10,000 Years – Modern Times
Around 10,000 years ago, we started to grow grains for consumption. Our diet became heavily composed of processed grains. With increased access to simple sugars, our daily intake of fibre from unprocessed food decreased. Consequently, the shift in our diet to depend largely on grains rather than fruits and vegetables decreased our consumption of vitamins and minerals. With easy access and low costs, the modern human diet has shifted towards higher consumption of animal-based products and processed foods, many of which are high in salt and fat. This raises concerns about our diet and its correlation with diseases that are only found in modern humans (e.g. obesity, hypertension, and autoimmune disease).

Then versus now

There is notably more protein and fiber intake in the paleolithic diet compared to the average daily North American diet; in contrast, the paleolithic diet has only a fraction of the current sodium intake. The Paleolithic diet also has a more complex carbohydrate intake compared to the modern average North American diet.

Why do we a prefer a diet that is high in sugar, salt and fat?

Our preference for sugar evolved because sugars are more common and easier to detect using our taste sensors than other nutrients. Our ancestors often used sweetness as an identifier of fruit ripeness since the nutrient content changes as the fruit ripens, with ripe fruit containing more sugar. We also crave sugar since our brains use carbohydrates as an energy source.

Salt is a unique ingredient. By itself, it does not taste pleasant like sugar and fat. However, we often prefer food with salt added. The reason why humans have evolved to crave salt is because we need salt to maintain the nerve impulses and fluid balance in our body. Furthermore, salt also enhances sweetness and blocks bitter tastes, something which is appealing to our taste buds.

Fat is a macronutrient that is high in energy. Homo sapiens evolved to prefer a high-energy diet in order to power their brains. Since fat involves the compact storage of energy, it operates as an ideal source and is stored by our bodies as emergency rations in the event that we cannot find food later on. To this end, we show a strong preference for fat, based on the smell, texture, and taste, because our brain has the incredible ability to access the energy content of foods high in fat with remarkable speed and accuracy.



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