FOOD NUTRITION: VITAMINS
Diagram
Vitamins that dissolve in water, and vitamins that dissolve in fat
Water-soluble vitamins
Vitamin C and the B vitamins. They dissolve in water, are not stored, and must be eaten often.
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Fat-soluble vitamins
Vitamins A, D, E and K. They dissolve in fat, are stored in fat and liver, and need fat to be absorbed.
Figure 1: Water-soluble vitamins dissolve in water and are not stored, while fat-soluble vitamins dissolve in fat and are stored in the body. Drawn in our own style from the vitamin chapters in Gropper et al., Advanced Nutrition and Human Metabolism, and in Kohlmeier, Nutrient Metabolism.
Introduction
Water-soluble vitamins and fat-soluble vitamins are both vitamins, which means both are organic compounds the body needs in small amounts, but they dissolve in different things and the body handles them differently. Water-soluble vitamins, vitamin C and the B vitamins, dissolve in water, travel in the blood, are not stored in the body, and are lost in the urine when more is eaten than needed. Fat-soluble vitamins, vitamins A, D, E and K, dissolve in fat, travel with fat, are stored in body fat and in the liver, and need fat in the meal to be absorbed.
Quick comparison
Table 1: Water-Soluble Vitamins compared with Fat-Soluble Vitamins
| Aspect | Water-Soluble Vitamins | Fat-Soluble Vitamins |
|---|---|---|
| Which vitamins | Vitamin C and the B vitamins: B1, B2, B3, B5, B6, B7, B9, B12 | Vitamins A, D, E and K |
| Dissolves in | Water | Fat |
| Stored in the body | No, or only in small amounts for short times | Yes, in body fat and in the liver |
| Needed in the diet | Often, because stores run out quickly | Less often, because stores last longer |
| Absorbed with | Absorbed directly from the gut into the blood | Absorbed with dietary fat, carried in chylomicrons |
| Lost in cooking | Lost in cooking water and by heat, because they dissolve in water | More stable in cooking, but lost with the fat that is thrown away |
| Excess eaten | Passed out in the urine | Stored, so a large excess can build up |
| Deficiency | Appears quickly when the diet lacks them | Appears slowly, because stores are used first |
| Main roles | Coenzymes in energy release and cell work, and vitamin C in collagen and defence | Vision, bone health, protection of membranes, and blood clotting |
| Food sources | Fruits, vegetables, whole grains, meat and milk | Oils, liver, eggs, dairy fat and leafy greens |
Scientific explanation
Definition
Water-soluble vitamins are vitamins that dissolve in water, namely vitamin C and the B vitamins, and they are not stored in the body in large amounts. Fat-soluble vitamins are vitamins that dissolve in fat, namely vitamins A, D, E and K, and they are stored in body fat and in the liver.
Working principle
Water-soluble vitamins dissolve in the water of food and of the gut, and they pass into the blood directly. Most of them act as coenzymes, helpers that enzymes need to release energy from food and to build cells, and vitamin C is needed to make collagen. Because they are not stored, the body needs a regular supply, and any excess is passed out in the urine. Fat-soluble vitamins dissolve in dietary fat, and they are absorbed with the fat into chylomicrons, the fat carriers of the gut, then stored in the liver and in body fat. Vitamin A is needed for vision, vitamin D for bone health, vitamin E protects membranes from oxidation, and vitamin K is needed for blood clotting.
Apparatus
The books used here name no laboratory apparatus for measuring or comparing either term, so no apparatus list is given.
Measurement procedure
The books used here give no standard laboratory procedure with volumes and steps for either term, so no procedure is invented here.
Factors affecting readings
For water-soluble vitamins, cooking in water and long cooking destroy or wash them out, and the freshness of the food decides how much remains. For fat-soluble vitamins, the fat in the meal decides absorption: a fat-free meal absorbs them poorly. Disease of the gut that stops fat absorption causes fat-soluble vitamin deficiency first. The books used here give no intake numbers, so none are stated.
Formulas and calculations
The books used here give no formula for either term, so no formula is given here.
Industrial applications
- Water-soluble vitamins: fruits and vegetables, eaten fresh and cooked briefly so vitamin C and B vitamins survive.
- Water-soluble vitamins: whole grains and meat, as sources of B vitamins.
- Fat-soluble vitamins: vegetable oils and dairy fat, as sources of vitamins A, D and E.
- Fat-soluble vitamins: liver and eggs, as sources of vitamins A and D.
- Fat-soluble vitamins: leafy greens, as sources of vitamin K.
- Both kinds: fortified foods, where vitamins are added to milk, flour and spreads.
Advantages and limitations
- Water-soluble vitamins, advantage: excess is passed out in the urine, so a large dose is less likely to build up.
- Water-soluble vitamins, limitation: they are not stored, so they must be eaten often, and they are lost in cooking water.
- Fat-soluble vitamins, advantage: they are stored, so the body can draw on them between meals.
- Fat-soluble vitamins, limitation: a large excess is stored too, so it can build up, and they need fat in the meal to be absorbed.
FAQ
What is the difference between water-soluble and fat-soluble vitamins?
Water-soluble vitamins dissolve in water, are not stored and must be eaten often, while fat-soluble vitamins dissolve in fat, are stored in fat and liver, and need fat to be absorbed.
Which vitamins are water-soluble?
Vitamin C and the B vitamins: B1, B2, B3, B5, B6, B7, B9 and B12.
Which vitamins are fat-soluble?
Vitamins A, D, E and K.
Why do water-soluble vitamins need to be eaten often?
Because the body does not store them, and the excess is passed out in the urine.
Does cooking destroy vitamins?
Water-soluble vitamins are lost in cooking water and by heat, while fat-soluble vitamins are more stable but are lost with fat that is thrown away.
References and further reading
- Gropper, Sareen S., Jack L. Smith and Timothy P. Carr. Advanced Nutrition and Human Metabolism. 7th ed., Cengage, 2016.
- Kohlmeier, Martin. Nutrient Metabolism: Structures, Functions, and Genes. 2nd ed., Academic Press, 2015, chapter 9, Fat-Soluble Vitamins, p. 479, and chapter 10, Water-Soluble Vitamins, p. 567.
- Google Books pages read for this article:
- Gropper, Sareen S., Jack L. Smith and Timothy P. Carr. Advanced Nutrition and Human Metabolism. 7th ed., Cengage, 2016 (Google Books page read)
- Kohlmeier, Martin. Nutrient Metabolism: Structures, Functions, and Genes. 2nd ed., Academic Press, 2015 (Google Books page read)
