Is the human body designed to eat carbs? Exploring nutrition and evolution

October 27, 2025 •

5 min read

Contrary to some modern diet trends, new research suggests that human ancestors developed multiple copies of the salivary amylase gene over 800,000 years ago, indicating a long evolutionary history with carbohydrate consumption. But is the human body designed to eat carbs, and what does this mean for today's diet?

Quick Summary

Human physiology is adapted to digest and use carbohydrates for energy, with evidence from evolution and metabolic function. The quality of carbs, distinguishing between complex and refined sources, is paramount for long-term health and well-being.

Key Points

Evolutionary Adaptation: Humans have evolved to digest and utilize carbohydrates efficiently, with genetic evidence showing an increase in starch-digesting enzymes over hundreds of thousands of years.
Primary Energy Source: Carbohydrates are the body’s preferred fuel, converting to glucose to power the brain and muscles for daily functions and physical activity.
Quality Over Quantity: The health impact of carbohydrates depends on their source. Complex carbs (whole grains, fruits) provide sustained energy and fiber, unlike refined simple carbs (sugars, processed foods) that cause rapid blood sugar spikes.
Essential for Gut Health: Dietary fiber, a type of carbohydrate, is critical for digestive health and feeds beneficial gut microbiota, contributing to overall well-being.
Balanced Approach: While alternative fuel sources exist, a balanced diet including high-quality carbohydrates is generally considered the most sustainable and beneficial approach for long-term human health.

Our Evolutionary Relationship with Carbohydrates

From an evolutionary standpoint, the human body has a long and complex relationship with carbohydrates. While earlier theories focused on a meat-heavy diet as the primary driver of human brain expansion, more recent evidence points to the crucial role of starchy plant foods. Concentrated starches from underground storage organs, like roots and tubers, provided the consistent, high-energy fuel needed to sustain a larger, more metabolically demanding brain. The advent of cooking further unlocked the energy potential of these starchy foods by making them more digestible. This was accompanied by a genetic adaptation: an increase in the copy number of the salivary amylase (AMY1) gene, which is essential for breaking down starch. This coevolution of cooking and increased amylase production significantly boosted the availability of dietary glucose, providing a substantial advantage to our omnivorous ancestors.

The Body's Primary Fuel Source

The human body is a highly efficient machine designed to use glucose, derived from the breakdown of carbohydrates, as its primary fuel source. Carbohydrate digestion begins in the mouth with salivary amylase and continues in the small intestine, where it is broken down into simple sugars like glucose, fructose, and galactose. Glucose is then absorbed into the bloodstream and distributed to cells throughout the body to produce ATP, the body’s main energy molecule. The brain, in particular, has a high and consistent demand for glucose, consuming about 20–25% of an adult’s basal metabolic energy.

Excess glucose is converted into glycogen and stored in the liver and muscles for later use. This stored energy is crucial for short-term fuel needs, such as during intense exercise. If these glycogen stores are full, excess carbohydrates are converted to triglycerides and stored as fat.

The Importance of Dietary Fiber

Dietary fiber, a type of complex carbohydrate, is indigestible by human enzymes but is critical for health. It passes through the digestive system largely intact, providing significant benefits:

Promotes digestive health: Fiber adds bulk to stool, preventing constipation and supporting regular bowel movements. Insoluble fiber acts as a bulking agent, while soluble fiber draws in water to form a gel-like substance that softens stool.
Feeds gut microbiota: The non-digestible fiber is fermented by beneficial bacteria in the large intestine, producing short-chain fatty acids (SCFAs). These SCFAs support the health of the gut lining and regulate metabolism.
Supports satiety and weight management: Fiber adds volume to food without adding calories, promoting a feeling of fullness that can help regulate calorie intake.
Reduces chronic disease risk: High-fiber diets are associated with a reduced risk of heart disease, type 2 diabetes, and certain cancers.

Carbohydrate Quality Matters

Not all carbohydrates are created equal, and the quality of the carbohydrates consumed is a major determinant of health outcomes. The glycemic index (GI) is a tool that ranks carbohydrate-containing foods based on their effect on blood sugar levels.

Comparison of Complex vs. Simple Carbohydrates


Feature	Complex Carbohydrates	Simple Carbohydrates
Digestion Speed	Slower, causing a gradual rise in blood sugar.	Faster, leading to rapid blood sugar spikes.
Primary Sources	Whole grains, vegetables, fruits, beans, and legumes.	Candies, sodas, pastries, white bread, and other highly processed foods.
Fiber Content	Generally high in dietary fiber.	Generally low in fiber.
Nutrient Density	Rich in vitamins, minerals, and phytonutrients.	Offer little to no nutritional value beyond calories.
Health Impact	Associated with improved gut health, stable energy, and reduced risk of chronic diseases.	Linked to increased risk of weight gain, type 2 diabetes, and heart disease with excessive intake.

Can the Body Survive Without Carbs?

While carbohydrates are the body’s preferred fuel, it is technically possible for the human body to function on a very low-carbohydrate or no-carbohydrate diet. In the absence of dietary glucose, the body can enter a state of ketosis, where it produces ketone bodies from the breakdown of fatty acids to use as an alternative fuel source for the brain and other tissues. This adaptation is a survival mechanism that allows humans to endure periods of prolonged fasting or food scarcity.

However, this does not mean that a no-carb diet is the optimal or most sustainable approach to nutrition for the average person. Severe carbohydrate restriction can lead to muscle breakdown to generate glucose for the brain, which is an undesirable outcome. Furthermore, a diet that eliminates or severely restricts carbohydrates may lack essential vitamins, minerals, and fiber found in healthy plant foods. Traditional low-carb diets, such as those of the Inuit people, often included carbohydrate sources like animal glycogen and tundra plants, in addition to unique genetic adaptations that are not universal.

Conclusion: The Answer is Not All or Nothing

So, is the human body designed to eat carbs? The answer is a qualified yes. Our evolutionary history and physiological adaptations, such as the amylase gene duplication, clearly demonstrate that our bodies are well-equipped to process and thrive on carbohydrates, particularly starchy plants. The key takeaway from both our ancestry and modern nutritional science is that the type and quality of carbohydrates matter profoundly.

While the body can resort to alternative energy sources in the absence of dietary carbohydrates, this is not an optimal state for long-term health and vitality. A balanced diet rich in high-quality, complex carbohydrates like fruits, vegetables, whole grains, and legumes is demonstrably beneficial for promoting gut health, regulating blood sugar, and reducing the risk of chronic disease. The human body is not only designed to eat carbs but has evolved to utilize them effectively, provided they are chosen wisely as part of a varied and nutrient-dense diet.

The Takeaway: It's All About Quality

The human body, particularly the brain, is highly adapted to use carbohydrates as its primary energy source.
Early human evolution was significantly influenced by the ability to utilize starchy plant foods, supported by genetic changes like the amylase gene duplication.
The distinction between complex and simple carbohydrates is critical for health, with complex carbs from whole foods offering sustained energy and vital nutrients.
Dietary fiber, a non-digestible carbohydrate, is essential for promoting digestive health, feeding beneficial gut bacteria, and managing chronic disease risk.
While the body can produce energy from fats via ketosis on a low-carb diet, this is more of a survival mechanism and may not be optimal for long-term health.

Frequently Asked Questions

No, not all carbohydrates are unhealthy. Healthy carbohydrate sources, such as fruits, vegetables, legumes, and whole grains, are rich in fiber, vitamins, and minerals. Unhealthy carbohydrates are typically refined and processed, like sugary drinks and white bread, which offer little nutritional value.

Simple carbohydrates are made of one or two sugar molecules, digested quickly, and cause rapid blood sugar spikes. Complex carbohydrates are long chains of sugar molecules that digest slowly, providing sustained energy and higher nutrient content.

The human body is capable of surviving without dietary carbohydrates through metabolic processes, but a zero-carb diet is not typically recommended for long-term health. It can lead to nutrient deficiencies, potential muscle loss, and may not provide the optimal fuel for sustained physical and cognitive function.

Carbohydrates, particularly from starchy plants, were vital for fueling the increased metabolic demands of the growing human brain. The development of cooking and the genetic evolution of salivary amylase enhanced our ancestors' ability to access this energy.

The Glycemic Index (GI) is a ranking system for carbohydrate-containing foods based on how they affect blood sugar levels. Low-GI foods produce a slower, more gradual rise in blood sugar, which is beneficial for managing blood sugar and promoting satiety.

Yes, carbohydrates are the body's primary fuel for moderate-to-high intensity exercise. Glycogen, the stored form of glucose from carbs, is crucial for fueling muscles during physical activity and maintaining performance.

The recommended intake of carbohydrates varies based on individual factors, but general guidelines suggest that 45% to 65% of daily calories should come from carbohydrates, prioritizing nutrient-dense whole food sources.

Dietary fiber, a type of carbohydrate, acts as a prebiotic, feeding the beneficial bacteria in your gut. This supports a healthy gut microbiome, which is linked to better immune function and overall digestive health.

In the short term, some individuals may experience 'keto flu' or 'brain fog' as their body adapts. Over the long term, insufficient glucose can affect optimal brain function, as the brain primarily relies on glucose for energy. However, the severity can vary widely among individuals.