Thiamin Riboflavin and Niacin

Functions. Thiamin, riboflavin, and niacin all play key roles as part of coenzymes in energy metabolism. They are essential in the release of energy from carbohydrates, fats, and proteins. They are also needed for normal growth.

Thiamin also plays a vital role in the normal functioning of the nerves. Riboflavin is part of coenzymes that help form the vitamin B6 coenzyme and make niacin in the body from the amino acid tryptophan.

Because thiamin, riboflavin, and niacin all help release food energy, the needs for these vitamins increase as caloric needs increase.

Food sources. Thiamin is widely distributed in foods, but mostly in moderate amounts (Figure 6-6). Pork is an excellent source of thiamin. Other sources include dry beans, whole-grain and enriched/fortified breads and cereals, peanuts, and acorn squash.

Milk and milk products are the major source of riboflavin in the American diet. Other sources include organ meats such as liver (very high in riboflavin), whole-grain and enriched/fortified breads and cereals, eggs, and some meats (Figure 6-7).

The main sources of niacin are meat, poultry, and fish. Organ meats are quite high in niacin. Whole-grain and enriched/fortified breads and cereals, as well as peanut butter, are also important sources of niacin. All foods containing complete protein, such as those just mentioned and also milk and eggs, are good sources of the precursor of niacin, tryptophan. Tryptophan, an amino acid present in some of these foods, can be converted to niacin in the body. This is why the RDA for niacin is stated in niacin equivalents. One niacin equivalent is equal to 1 milligram of niacin or 60 milligrams of tryptophan. Less than half the niacin we use is made from tryptophan.

figure 6-6 FOOD SOURCES OF THIAMIN

grains

RDA

1 Food and Serving Size

Milligrams

Men

Women

1 Rice Krispies, 11/4 cup

0.87

1.2

1 Rice, white, long grain, 1/2 cup

0.55

1.2

1 Corn Chex, 1 cup

0.38

1.2

1 English muffins, 1 muffin

0.25

1.2

1 Rice, white, long-grain, cooked, 1/2 cup

0.13

1.2

1 White bread, 1 slice

0.12

1.2

1 Whole wheat bread, 1 slice

0.10

1.2

meats, poultry, fish, and alternates

RDA

1 Food and Serving Size

Milligrams

Men

Women

1 Pork chops, pan-fried 3 oz.

0.97

1.2

1 Pork, cured ham, 3 oz.

0.82

1.2

1 Pork, ribs, braised 3 oz.

0.43

1.2

1 Beans, navy, cooked, 1/2 cup

0.22

1.2

1 Beans, Great Northern, cooked, 1/2 cup

0.14

1.2

fruits and vegetables

RDA

Food and Serving Size

Milligrams

Men

Women

1 Peas, cooked, 1/2 cup

0.23

1.2

1.1

1 Orange juice, 1/2 cup

0.14

1.2

1.1

1 Acorn squash, 1/2 cup

0.12

1.2

1.1

1 Source: U.S. Department of Agriculture, Agricultural Research Service, 2004. USDA Nutrient 1 Database for Standard Reference, Release 17. Nutrient Data Laboratory Home Page, 1 http://www.nal.usda.gov/fnic/foodcomp.

Deficiency and toxicity. Deficiencies in thiamin, riboflavin, and niacin are rare in the United States, in large part because breads and cereals are enriched with all three nutrients. General symptoms for B-vitamin deficiencies include fatigue, decreased appetite, and depression. Alcoholism can create deficiencies in these three vitamins due in part to limited food intake.

Toxicity is not a problem except in the case of niacin. Nicotinic acid, a form of niacin, is often prescribed by physicians to lower elevated blood cholesterol levels. Unfortunately, it has some undesirable side effects. Starting at doses of 100 milligrams, typical symptoms include flushing, tingling, itching, rashes, hives, nausea, diarrhea, and abdominal discomfort. Flushing of the face, neck, and chest lasts for about 20 minutes after a person takes a large dose. More serious side effects of large doses include liver damage and high blood sugar levels.

figure 6-7 FOOD SOURCES OF RIBOFLAVIN

grains

grains

Food and Serving Size

Milligrams

Men

Women

Total, 3/4 cup

2.42

1.3

1.1

Wheaties, 1 cup

0.85

1.3

1.1

White bread, 1 slice

0.09

1.3

1.1

Whole-wheat bread, 1 slice

0.06

1.3

Food and Serving Size

Milligrams

0.53

Women 1.1

Food and Serving Size

Milligrams

0.53

Women 1.1

Milk, all types, 1 cup

0.45

1.3

1.1

Cottage cheese, low-fat, 1/2 cup

0.21

1.3

1.1

1

fruits and vegetables

RDA

Food and Serving Size

Milligrams

Men

Women

Mushrooms, cooked, 1/2 cup

0.23

1.3

1.1

Spinach, cooked, 1/2 cup

0.21

1.3

1.1

Prunes, 1/2 cup

0.12

1.3

1.1

1

meats, poultry, fish, and alternates

RDA

Food and Serving Size

Milligrams

Men

Women

Beef, liver, cooked, 3 oz.

2.91

1.3

Shrimp, breaded and fried, 6-8 shrimp

0.90

1.3

Egg, cooked, 1

0.26

1.3

Beef, prime rib, roasted, 3 oz.

0.18

1.3

Beef, ground, 75% lean, broiled, 3 oz.

0.15

1.3

Source: U.S. Department of Agriculture, Agricultural Research Service, 2004. USDA Nutrient Database for Standard Reference, Release 17. Nutrient Data Laboratory Home Page, http://www.nal.usda.gov/fnic/foodcomp.

Source: U.S. Department of Agriculture, Agricultural Research Service, 2004. USDA Nutrient Database for Standard Reference, Release 17. Nutrient Data Laboratory Home Page, http://www.nal.usda.gov/fnic/foodcomp.

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