What’s a carb?
A common way to classify food is by dividing it up into 3 kind of molecules called fat, carbohydrate and protein. These are the 3 macronutrients (ignoring alcohol). Fatty acids make up fat, amino acids make up protein and sugars make up carbohydrate. Calories from a diet can come from these 3 macronutrients. A low-carbohydrate diet is one necessarily higher in fat and a low-fat diet is one necessarily higher in carbohydrate. How much fats or carbs one eats can vary a lot. The amount of protein varies less. Humans must eat a minimal amount of fats and protein from animal sources but can do without dietary carbohydrate .
How low do you have to go?
Some researchers say a diet qualifies as low-carb when calories from carbohydrates are restricted to 10% of total calories . This is neither right or wrong. It is a somewhat arbitrary cutoff point derived relative to the more typical percentage of carbohydrates in modern American diets hovering around 50% (as of 2006) .
Origin story of low-carb diets
Where it all begins depends on how far back you want to go. Low-carb high-fat diets, known as LCHF nowadays, were eaten amongst many of our paleolithic ancestors . More recently, the popular Banting diet of the early 1900s was a low-carb diet . Jump to the 1980s and the Atkins diet  is also a low-carb high-fat diet. The ketogenic diet, unheard to most people even today, is a lesser known low-carb diet that is defined by the metabolic state it induces called ketosis. It results from the presence of ketones in the blood arising from the restriction of carbohydrates first and protein second.
What are examples of low-carb foods and low-carb meals?
Here’s an examples of increasingly fancy low-carb meals.
Bacon & eggs, just coffee – black.
Beef liver, smoked salmon & sliced avocado with blueberries. Tea to sip.
Beluga caviar & sardines contrasted with veal chops & olives. Dark chocolate and Kombucha to cleanse the palette.
Did human eat more fat or carbs, historically?
Throughout history humans have eaten particularly varied diets, especially compared to other animals. Humans can be carnivores, eating nearly anything that can fly, walk, crawl or swim. They can also eat large amounts of vegetables, nuts and fruit given they eat sufficient amounts of animal products. Basically, we’re obligate carnivores (our biology does well on animal sources alone) but preferential omnivores (vegetation is always included when available). Here’s an example of the range from high to medium and low-carb diets eaten by our hunter-gatherer ancestors [7, 8, 9].
After pooling data from 63 hunter-gatherer groups, one estimate puts the carbohydrate content of the most common diet at 10% to 15% of total calories .
My ancestors ate lots of starch and fruit in their diet, does this mean I can’t go low-carb?
No, but it’s a great question. It’s hard to tell how much and how exactly the geography of genetic history matters to what we eat. There are many unanswered questions in this regard. For example, many people assume that the more copies of a gene you have for digesting amylase (a kind of sugar), the better your biology will handle carbs. This isn’t true. There’s no association between the number of AMY1 copies you carry (the gene to digest amylase) and your likelihood to become obesite . Nevertheless, there are examples where the geography of genetics does affects the foods we can eat. For example, people from places where cattle was reared for a few thousand years tend to have a mutation in the gene encoding for lactase, the enzyme allowing the digestion of sugar-milk (lactose) in infancy . Those carrying the mutation can keep digesting lactose beyond infancy.