A syllogism is a three-step deductive argument that moves logically from two premises to a conclusion. For example,
Premise #1: All whole foods are nutritious foods.
Premise #2: All whole foods are tasty foods.
Conclusion: Some tasty foods are nutritious foods.
If we assume that both of the premises are true, then logically the conclusion must also be true.
One way to express this is with a Venn Diagram.
The circle on the left represents all nutritious foods. The circle on the right represents all tasty foods. In the middle are whole foods, which are both nutritious and tasty. And we can see from the Venn Diagram that the conclusion of our syllogism is valid: Some tasty foods are also nutritious foods.
In November 1935 the explorer Vilhjalmur Stefansson published a series of articles called Adventures in Diet in Harper's Monthly Magazine. In these he described the health and diet of the Inuit, an indigenous people group of the arctic and subarctic of Canada. Sometimes low-carbers like to use Stefansson's descriptions to design scientific syllogisms. Once again, we will assume that the premises are accurate.
Premise #1: The early 20th century Inuit were free of the diseases of civilization.
Premise #2: The early 20th century Inuit ate meat, fat, and very little plant matter.
Conclusion: If a person in the 21st century eats meat, fat and very little plant matter, he or she will be free of the diseases of civilization.
Let's look at the Venn Diagram.
On the left are people who are free of the diseases of civilization. (For those unfamiliar with the term, the diseases of civilization have a greater prevalence in Westernized societies and include dental caries, obesity, heart disease and type-2 diabetes.) In the circle on the right are people who eat meat, fat and very little plant matter. In the center, occupying both the right and left circle, are the early 20th century Inuit. The Venn Diagram shows that there is an area of overlap between freedom from diseases of civilization and Inuit eating habits. The early 20th century Inuit fall in that area. But where do we find 21st century eaters of meat, fat and very little plant matter? They are not on the diagram, or if they are, we have no idea if they are in the area where the two circles overlap. The syllogism is invalid.
The other problem with the second syllogism is the definition of terms. Premise #2 states that, "The early 20th century Inuit ate meat, fat, and very little plant matter." For the Inuit, meat and fat meant seal, whale and polar bear, as well as arctic fish, which was sometimes eaten rotten. Plants meant grasses, tubers, roots, berries and seaweed. How many 21st century low-carbers would be willing to eat this type of food for an entire lifetime?
Science is done by making observations and formulating hypotheses. Logic does enter into the process, but logic is not enough. Once the hypothesis is formulated, it must be tested. The essential difference between science and syllogism is the experiment. The well-designed and repeatable experiment is the gold standard of science. If it turns out according to the hypothesis, the hypothesis remains intact and is subject to further testing. If the experiment does not turn out according to the hypothesis (and at least 90% of the time it will not), the hypothesis may need to be refined.
It is tempting to speculate that non-Inuit people living in Western cultures will be able to eat beef, pork, chicken and produce purchased from grocery stores or local farmers and experience the same health benefits observed in the early 20th century Inuit. However, without experiments comparing these two diets head-to-head in people of similar genetic background, engaged in similar lifestyles, over many years, it must be acknowledged that this type of justification for low-carb eating is based on syllogism, not on science.
Coincidentally, Jenny at Bloodsugar 101 Diabetes Update has just posted on the use of idyllic fantasies as arguments to support low-carbing: Let's Not Twist History To Support Our Beliefs.