Conventional nutrition advice often presents vitamin C and dietary fiber as essential components of a healthy diet. However, when examined through the lens of human physiology, evolutionary biology, and metabolic adaptation, a different picture emerges. Both vitamin C and fiber can be beneficial in certain contexts, but neither is universally or strictly required for human survival and proper function. The body has built-in mechanisms that reduce or eliminate the need for them under specific dietary conditions, particularly when carbohydrate intake is low and nutrient density is high.

Why Vitamin C Is Not Universally Required

Vitamin C is classified as an essential nutrient because humans cannot synthesize it. However, the amount needed varies dramatically depending on the metabolic environment. The primary reason for vitamin C deficiency is competition with glucose. Vitamin C and glucose use the same cellular transport pathways. When carbohydrate intake is high, glucose dominates these pathways, forcing the body to require higher vitamin C levels to move what little is available into cells. This is why modern diets, which are often high in sugar and carbohydrates, come with increased vitamin C requirements.

When carbohydrate intake is low, the body’s demand for vitamin C decreases sharply. Ketogenic or carnivorous populations historically survived on diets with almost no plant matter and very low vitamin C intake without developing scurvy. Several factors explain this:

1. Low carbohydrate intake reduces competition for vitamin C transport, so less is needed.
2. Animal foods contain small amounts of vitamin C, especially when fresh, which is often enough when demand is low.
3. Collagen turnover decreases on high-fat, adequate-protein diets, further reducing vitamin C requirements.
4. The antioxidant load is lower on low-carbohydrate diets because fewer unstable plant compounds are consumed, decreasing oxidative stress and, therefore, vitamin C usage.

In this state, vitamin C does not need to be ingested in large quantities. The body becomes efficient with minimal amounts, and deficiency becomes rare.

Why Fiber Is Not Required

Fiber is widely promoted as necessary for digestion, gut motility, and metabolic health. Yet none of these claims hold universally true, and fiber has never been classified as physiologically essential. There are populations with historically zero fiber intake who experienced no digestive or metabolic issues. The notion that fiber is required stems from modern dietary patterns that rely heavily on processed carbohydrates.

Here is why fiber is not a dietary requirement:

1. Fiber is not absorbed or used as a nutrient by the human body. It passes through intact or is fermented by gut bacteria.
2. The need for fiber increases only when diets are high in carbohydrates and low in fat. Fiber slows glucose absorption, improving blood sugar stability. When carbohydrates are minimal, this function becomes irrelevant.
3. Human intestinal length, stomach acidity, and enzymatic profile are optimized for protein and fat digestion, not plant fiber breakdown.
4. Low-fiber, high-fat diets naturally soften stools through increased bile acid production and fat lubrication. Constipation often improves, not worsens, on these diets.
5. Fiber can introduce digestive irritation, bloating, and inflammation for many people, especially soluble plant fibers that ferment aggressively.

The human digestive system does not depend on fiber to function. It depends on hydration, electrolytes, and adequate dietary fat far more than it depends on plant roughage.

Context Determines Necessity

The modern belief that vitamin C and fiber are required stems from diets that create the conditions for those requirements. High-carbohydrate, high-sugar, low-fat diets increase vitamin C demand and create gastrointestinal issues that fiber temporarily alleviates. Remove the dietary stressors, and the perceived requirements vanish.

Physiologically, neither vitamin C nor fiber is universally essential. The body’s adaptations, metabolic pathways, and digestive structure are fully capable of maintaining health without them under the right dietary conditions.

Conclusion

Vitamin C and fiber are not absolute dietary requirements. They can be helpful depending on one’s diet, but the human body is not dependent on them for survival. When carbohydrate intake is low and nutrient-dense foods dominate, vitamin C requirements decrease dramatically, and digestive health no longer relies on fiber. Understanding this distinction helps clarify that essential nutrients are context dependent, and human physiology is far more adaptable than most modern guidelines suggest.