In recent years, diabetes and obesity have rapidly increased in both developed and developing countries, becoming medical and social problems [1]. This means that overnutrition is a serious problem, and measures such as calorie and carbohydrate restriction are necessary. Meanwhile, millions of years ago, Homo sapiens evolved from primitive man, ape-man, and then man, emerging in Africa approximately 300,000 years ago. At the time, they were not the only human species on Earth. Neanderthals roamed the steppes of Europe, Denisovans spread across Asia, and a dwarf human known as "hobbits" existed in Indonesia. However, these species became extinct by approximately 40,000 years ago. Homo sapiens is the only species remaining today.

Homo sapiens left Africa approximately 60,000 years ago and arrived in the Japanese archipelago around 38,000 years ago during the Paleolithic period. This continued for 22,000 years, forming the world's most advanced civilization at the time [2]. The Yayoi period began 2,500 years ago, when rice cultivation became established and continues until now. In 1949, Tadahiro Aizawa excavated chipped stone tools made of obsidian at the Iwajuku site in Gunma Prefecture, Japan [3]. This proved the existence of the Paleolithic period in the Japanese archipelago, and then tens of thousands of other archaeological sites have been discovered [4]. On the other hand entire Eurasian continent had only a few hundred archaeological sites, suggesting that the prosperity of Japanese civilization swept the world at that time. These materials have been registered as national tangible cultural propertie. They are highly regarded academically and historically as important documents that opened the door to research into the Paleolithic period in Japan [5].

Climate influences taking food. Japan's Paleolithic period coincided with the last glacial period, the Würm glacial period, and was extremely cold [6]. Fortunately, the Pacific side of the Japanese archipelago is served by the warm Kuroshio Current. This is one of the world's largest ocean currents (70-150 km wide, 2-7 km/h), flowing north from the Philippines off the coast of Taiwan and along Japan's southern coast. Its unique feature is that it keeps the coastal climate warm and provides rich fishing grounds for tuna, bonito, and other fish. Therefore, even though it was an ice age, it is thought to have been considerably warmer than the cold conditions of the rest of Eurasia. It is believed that this regional characteristic and warm climate allowed civilization to develop.

What did people eat during the Paleolithic period? Homo sapiens began inhabiting the Japanese archipelago during the Paleolithic period, approximately 38,000 years ago. Because of the extremely cold conditions during the last ice age (the Würm glaciation), only coniferous trees were available. This meant that there were no broad-leaved trees that bore fruit, where no acorns, chestnuts, or apples were found. The only herbivorous foods available were wild yams, cowberries, and pine nuts [7]. Furthermore, fishing techniques were not yet developed, so people ate only land animals. It means that they likely hunted and ate Naumann's elephant, giant deer, elk, deer, wild boar, and hares. In Hokkaido, they likely also ate mammoths. Although Paleolithic people in other parts of the world may have consumed carbohydrates, meat was simply the only food available in Japan.

The land also changes depending on the climate. During the ice age, it was extremely cold and water on land froze. When a large amount of frozen water on land, the amount of water flowing into the ocean drastically decreased. As a result, sea levels dropped by approximately 130 meters during the ice age. The four major straits in the Japanese archipelago (Tsushima, Kanmon, Soya, and Mamiya) then became connected to land, allowing people to travel between the Korean Peninsula and Russia on foot [8]. However, the Tsugaru Strait was so deep that it consistently prevented Hokkaido from connecting to Honshu. Meanwhile, Siberia and Hokkaido were connected by land, allowing animals like Naumann's elephant to migrate there. However, the Tsugaru Strait was so deep that it never connected to land even during the ice age, preventing mammoths from reaching Honshu.

As described above, the Paleolithic period in Japan lasted for approximately 22,000 years. During this period there was almost nothing to eat other than animal meat. In other words, people were naturally in a situation where they restricted their carbohydrate intake.  Given this history, it is possible to call this low-carbohydrate diet (LCD) situation for "Neo-Paleolithic diet." Using the Bayesian dating model, diachronic analysis was conducted for the changes in stone tools for structure, reduction techniques and raw materials [9]. When environmental conditions has improved, hunter-gatherers increased their sedentarization during abundant forests.

Paleo diet has been recently in focus [10]. It is originally paleolithic diet, that is the attempt to replicate the food situations consumed by ancient Paleolithic humans into modern diet. Generally, Paleolithic people lived a hunter-gatherer life style, and usually took animal products and wild plant foods [4]. The main structure is shown in the following. The recommended foods include vegetables, nuts, fruits, eggs, fish, seafood, poultry, lean meat, healthy oils and fats (olive oil, nut oils). Restricted foods include rice, wheat, dairy products, legumes (tofu, natto, lentils), refined sugars, processed foods, most processed oils and fats.

Paleo diet is based on the idea that the modern rise in obesity, type 2 diabetes (T2D), and cardiovascular disease (CVD) is related to a diet centered on agriculture and processed foods. This long-standing diet throughout human history may be also beneficial to modern-day health. In the light of theoretical background, paleolithic people took natural diverse meal before the initiation of agriculture. It is only recent era that we eat agriculturally obtained foods, including grains, products and so on. From paleophilosophy point of view, human genetic program would be most suitable for the previous paleolithic environment. It is because recent meal patterns in modern society would be the cause of non-communicable diseases (NCDs) [11].

Both Paleo diet and LCD are compared for their elements [12-14] (Table 1) (Figure 1). It is merely a guideline for typical scope, depending on the protocol and subject. Several similarities have been found between them as follows [15]. They are i) Reduction of carbohydrates and refined sugars: both diet methods essentially restrict refined carbohydrates such as flour, sugar and rice, ii) Elimination of processed foods: both diets reduce processed foods and artificial additives and encourage foods closer to their original form. and iii) Short term efficacy on body weight and plasma blood glucose levels: lots of evidence has been found that LCD shows clinical effect for short-term weight reduction and glucose control, and some reports are observed that Paleo diet shows short-term improvement for lipid metabolism and weight control [16].

Table 1: Comparison of Diet Pattern and Elements.

These are all expressed by the approximate data.

Figure 1: Image Comparison for Paleo and LCD.

Clinical effect was reported for Paleo and LCD. As Paleo diet, a systematic review and meta-analysis was conducted for 159 cases [17]. As a result, it showed greater short-term improvements than other control diets. They included waist circumference -2.38 cm, triglycerides -0.40 mmol/L (-35.4 mg/dL), systolic BP -3.64 mmHg, diastolic BP -2.48 mmHg, HDL-C 0.12 mmol/L (4.6 mg/dL), and fasting blood glucose -0.16 mmol/L (-2.8 mg/dL). As the latest report, systematic reviews with meta-analysis of RCT was conducted [18]. LCD interventions showed HbA1c -0.42% without considering period, -0.28% for 3 months, -0.40% for 6 month and -0.31% for >12 months compared with control diets.

Some limitation may be present for the comparison with Paleo and LCD. Regarding nutritional composition, the former is not simply a carbohydrate restriction, but rather focuses on eliminating or promoting certain food groups. Following the Paleolithic pattern, it may focus on unprocessed and whole foods. The latter clearly specifies the carbohydrate limit with a numerical value, and may not specify whether processed or unprocessed foods are acceptable.

In summary, historical background of Paleolithic period and its comparison with LCD has been described. We have entered an era where dietary therapy tailored to each individual is in demand. We hope that the information presented here will be useful to many patients and medical professionals in clinical settings.

Conflict of interest:

The authors declare no conflict of interest.

Funding:

There was no funding received for this paper.

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