Blog Directory - Blogged foodliterate: February 2009

Saturday, February 28, 2009

The ABC's of Vitamins - Vitamin B2

I'd like to introduce you to vitamin B2; it is actually a group of compounds called flavins which contains riboflavin, riboflavin-5'-phosphate (FMN) and riboflavin-5'-adenosyldiphosphate (FAD). Riboflavin's name comes from what it looks like, both physically and chemically. It is a florescent yellow-orange color and flavin comes from flavus meaning yellow in latin the ribo comes from ribitol which is the sugar part of the molecule.

FMN and FAD exist primarily as part of flavoproteins (flavin enzymes) and living cells require them. They work in the oxidoreductive processes - that is they can accept hydrogen atoms - and are used in biological processes like the conversion of pyruvate to acetyl-CoA (for fatty acid metabolism).

This is also one of the vitamins we need to get from our food. Milk, cheese, meat, yeasts, eggs, wheat bran, liver and kidney are all good sources of this vitamin. Riboflavin is absorbed in the intestine; FAD & FMN are converted to riboflavin before they are absorbed. Some of the absorbed riboflavin is converted by the body to FMN and most of that FMN is then converted to FAD in the cells. Vitamin B2 is used in energy production and the conversion of tryptophan to niacin.

Again, this is not a vitamin that is commonly deficient, both due to supplementation and its availability in commonly consumed foods. It doesn't even have any really fun symptoms, you'd most likely experience cracked lips and inflammation of the tongue. Riboflavin is currently being evaluated as a treatment in the prevention of migraines.

So, you've met two of the B vitamins, more to come in the weeks ahead. In the meantime, eat well and be well!

Saturday, February 21, 2009

The ABC's of Vitamins - Vitamin B1

The vitamin du jour is Thiamin (or Thiamine depending on where you are from) which is also known as vitamin B1; it was discovered and named by Robert R. Williams in the early 1930's. Thiamin is found in all plants and animals, but pulses, nuts, cereals/grains, yeasts and pork contain larger quantities than beef, chicken, eggs, veggies and fruits.

Thiamin is not one of the vitamins we can produce so it has to come from our diet. Thiamin is usually found in one of three phosphorylated forms: monophosphate ester, triphosphate ester, and thiamin pyrophosphate (TPP). The triphos form has a role in nerve transmission but the TPP has a much larger role in the body.

TPP is a co-enzyme for several metabolic pathways. It works in the decarboxylation and transketolation processes involved in turning carbohydrates in to energy (tricarboxylic acid cycle). In the body TPP is hydrolyzed to free thiamin in your intestines where it is converted back to TPP in your cells (seems a little silly - huh?). Our cardiovascular and nervous systems need carbohydrates and carbohydrate metabolism needs thiamin - so the amount you need depends is directly dependent on the amount of carbohydrates you eat.

Thiamin is considered to be one of the vitamins with a high bioavailability, probably due to the fact that is most often found in the form our bodies can use (TPP) and because so many foods are supplemented with it, so deficiencies are pretty uncommon. That doesn't mean it can't happen - alcoholics, persons with intestinal issues (especially diarrhea and vomiting), genetic malabsorption issues or those who only eat junk food can all run into issues with deficiency. Some of the symptoms associated with a lack of vitamin B1 are anorexia, muscle weakness, and cardiovascular irregularities. If you really get deficient, you can look forward to paranoia, manic/depressive episodes, confusion and beriberi. Just so you can avoid these conditions keep these facts in mind: thiamin is sensitive to heat and baking soda can inactivate it; while tea and coffee can interfere with its absorption.

So, now you know about the first of the B vitamins - quite a large family as you will see, so come back to meet its cousins!

Sunday, February 15, 2009

The ABC's of Vitamins

I received some ribbing about jumping right in to the vitamins without starting from the basics. Since I am guilty as charged, and in an effort to make amends, I am going to take a step backward before I continue to move forward with the B-vitamins. The word vitamin comes from the Polish scientist Casimir Funk who thought they were “vital amines” (meaning nitrogen containing) and called them vitamines. When it was later determined that not all of them had nitrogen, they simply dropped the ‘e’ from the end giving us “vitamin”.

Vitamins are organic compounds that are essential to us, in order to maintain bodily functions, in very small amounts. There are about 13 vitamins that we need to maintain our health, one of which we can make (D) and another the bacteria in our gut can make for us (K) and the rest of which we need to obtain from our diets. While not used for energy, some vitamins are required for energy production. Other vitamins are used much like hormones (D especially) and others as co-enzymes (B group).

The vitamins were named alphabetically, so why does it go A, B, C, D, E, K? Well, originally lots of things were thought to be vitamins that turned out not to be. What was vitamin F is really essential fatty acids, vitamin G was renamed Riboflavin (B2), vitamin H was renamed as Biotin (B7), vitamin J is catechol… you get the point.

Obviously some of the vitamins have subsets – the B vitamins being the most familiar, but there are others; and they are further divided into water soluble and fat soluble. Fat soluble vitamins include: A, D, E, K and the carotenoids. Water soluble vitamins include: the B’s (thiamin, riboflavin, niacin, pyridoxine, pantothenic acid, biotin, folate, cyanocobalamin) and C. ). Excess fat soluble vitamins are stored for future use and most of the excess water soluble vitamins are excreted and so must be ingested daily.

The US government has distributed a Recommended Daily Amount (RDA) for many of the vitamins. (The RDA is calculated as the daily intake that is sufficient for 97-98% of healthy individuals in a particular age/gender group.) You’ll see the effects of this on a nutrition data panel on the foods you purchase as % daily value. Most Americans get all the vitamins they need from the foods they consume; the fact that my industry adds (supplements) many of the foods consumed definitely helps in this regard. But some still choose to take supplements daily. There are some groups for whom supplementation makes good sense: elderly, pregnant, Chron’s disease, low calorie diets, high protein (low veggie) diets, and those with intestinal issues (diarrhea).

So, now that the basics have been covered, I’ll get back on the bus and take us to B-town - the vitamin B group. Hope to see you there!

Saturday, February 7, 2009

The ABC's of Vitamins - Vitamin A Carotenoids

Last week I discussed preformed vitamin A and this week I'll be talking about provitamin A, also known as carotenoids. Carotenoids (beta-carotene, lycopene, xanthophylls) are compounds found in plants and photosynthetic microorganisms that work as light-harvesting pigments with chlorophyll. Animals cannot produce carotenoids and must get them from their diets.

A molecule of retinol must be present in the structure of a carotenoid in order for it to possess provitamin A activity. The most common and well known of the carotenoids is beta-carotene which has 2 retinol molecules and therefore the highest provitamin A activity. Only about 50 of 500 carotenoids are considered provitamin A.

Fruits and vegetables are where we get our carotenoids. Yellow, orange and red are where we expect to find them, but they are also present in dark green leafy vegetables too. As with preformed vitamin A, carotenoids are available as supplements, primarily as beta-carotene. Crystalline beta-carotene supplements are absorbed at about 50% efficiency; while a raw carrot is only absorbed at about 1% efficiency. Luckly, cooking vegetables increases the efficiency of carotenoid absorption (sorry all you raw food fans!).

Carotenoids that are not used immediately by the body are stored in the fatty tissues, liver and organs much like preformed vitamin A. However, since the carotenoids are not yet in the biologically active form, they are perfectly safe and do not induce toxicity. Carotenoids consumed in large quantities can cause hypercarotenosis (a yellowing of the skin) which is reversible and doesn't have any long-term toxic effects. No USRDI has been established for carotenoids, but 10 -30 mg/day seems to be the target.

Much of what you hear about beta-carotene involves its role as an antioxidant. Carotenoids have the ability to trap peroxyl free radicals and to deactivate singlet oxygen molecules. This appears to be due to their extensive conjugated double bond systems and helps us by reducing some of the mechanisms associated with some cancers. In addition to this, carotenoids help enhance our immune system. See, your mom was right all along - you have to eat your fruits & vegetables. They may just help to save your life!

Sunday, February 1, 2009

The ABC's of Vitamins - Vitamin A

I've spent a fair bit of time discussing the macronutrients (protein, fat, carbs), so I thought it was time to start on the micronutrients. Because I am a scientist and like things orderly, I'm going to go alphabetically rather than oil vs. water soluble. That means today's vitamin is A.

Vitamin A isn't a single thing, rather it is a generic term for compounds (other than carotenoids) having the biologic activity of retinol. The retinoids include: retinol, retinaldehyde and retinoic acid. These compounds are referred to as preformed vitamin A because they do not need to undergo metabolic conversion to be biologically active.

Vitamin A is essential to several of our life processes like metabolism, skeletal and soft tissue growth, formation and maintenance of epithelial tissues (skin & mucous membranes), reproduction and vision (although retinoic acid cannot support these last 2 because they need retinol or retinaldehyde).

Dietary sources of preformed vitamin A are animal tissues and milk - the animals convert carotenoids into vitamin A which we then consume as meat, milk, cheese, butter, etc. We can also get our vitamin A from supplements. Vitamin A is measured in IU (international units) and 1 IU is equal to the biologic activity of 0.3 micrograms of retinol. The USRDI for vitamin A is 3000 IU (900 micrograms) with an upper limit (the maximum daily intake that can be safely consumed) of 10000 IU (3000 micrograms). Vitamin A deficiencies are not very common, at least not in developed nations, but if you don't eat dairy, fruits or vegetables you could get into trouble. Early symptoms of deficiency include night blindness, dry skin and susceptibility to infection. If left untreated, it can result in permanent blindness. Vitamin A can become toxic since it is stored in the fatty tissues, liver and organs, but only if you are taking massive amounts of supplements or eating nothing but liver.

Preformed vitamin A absorption occurs in the small intestine and about 5-20% of the vitamin A ingested is not absorbed and is eliminated from the body. Everyone has a different absorption ratio, but typically vitamin A is absorbed at only 20-50% efficiency. In order to use and metabolize vitamin A, it needs some friends. Since vitamin A is an oil soluble vitamin, it stands to reason that it is better absorbed when consumed with fat. But vitamin A also needs protein; the lack of protein will result in a lack of vitamin A metabolism due to a decrease in enzyme levels. Zinc is also needed; a lack of it causes low plasma vitamin A levels even when vitamin A supplementation is given. And vitamin E is necessary; a lack of vitamin E causes a lack of vitamin A to be stored in the liver.

Next time I'll talk about provitamin A, also known as carotenoids, so eat well to be well!