Folic acid generally has significantly higher bioavailability than naturally occurring food folate, with food folate commonly estimated to be approximately 50% as bioavailable as folic acid, though this can vary widely.
Understanding Folate and Folic Acid Bioavailability
To grasp the difference, it's essential to understand what folate and folic acid are and what bioavailability means.
- Folate is the natural form of vitamin B9, found in a variety of foods like leafy green vegetables, legumes, fruits, and liver. It exists in different chemical forms (polyglutamates) within food.
- Folic acid is the synthetic, oxidized monoglutamate form of vitamin B9, commonly used in dietary supplements and to fortify foods (like cereals, bread, and pasta).
Bioavailability refers to the proportion of a nutrient that is absorbed from the diet and becomes available for use or storage in the body.
Key Differences in Absorption
The primary reason for the difference in bioavailability lies in how each form is absorbed:
- Folic Acid: When consumed, folic acid does not require enzymatic digestion and is absorbed almost completely (nearly 100% on an empty stomach). This makes it highly efficient at increasing folate levels in the body.
- Food Folate: Natural folate in food is mostly in the form of polyglutamates. Before it can be absorbed, these polyglutamates must be broken down into monoglutamates by an enzyme called folate conjugase (or gamma-glutamyl hydrolase) in the digestive tract. This deconjugation process is often incomplete and can vary between individuals and food sources, leading to lower and more variable absorption.
Bioavailability Comparison
The bioavailability of food folate is significantly less consistent and generally lower than that of folic acid. While a common estimate for food recommendations places food folate at 50% of folic acid's bioavailability, studies have shown its absorption to vary considerably. Data on food folate's bioavailability can range anywhere from 30% to 98% compared to folic acid.
To summarize the general differences:
| Nutrient | Source | Relative Bioavailability (vs. Folic Acid) | Absorption Mechanism | Stability |
|---|---|---|---|---|
| Folic Acid | Supplements, fortified foods | ~100% (especially on empty stomach) | Absorbed directly as a monoglutamate; no digestion needed | Highly stable |
| Food Folate | Leafy greens, legumes, fruits, liver | 30%–98% (commonly estimated at 50%) | Requires enzymatic deconjugation into monoglutamates | Less stable, prone to degradation |
Practical Implications for Folate Intake
Due to these differences, dietary recommendations and nutrient labeling often use Dietary Folate Equivalents (DFEs) to account for the varying bioavailabilities.
- 1 mcg DFE is equivalent to:
- 1 mcg of food folate
- 0.6 mcg of folic acid from fortified foods or supplements consumed with food
- 0.5 mcg of folic acid from supplements consumed on an empty stomach
This system ensures that when you see a DFE value on food labels or in dietary guidelines, it reflects the amount of folate your body can actually utilize, irrespective of its source. This is particularly important for groups with higher folate needs, such as pregnant women, to prevent neural tube defects.
By understanding the distinct bioavailability of folate and folic acid, individuals and health professionals can make more informed choices regarding diet and supplementation to ensure adequate vitamin B9 intake.
