Health Concerns Related to Protein Intake.. pussy government people trying not to admit everyone should go veg ;)

Proteins and amino acids are supplied by the diet as well as by the recycling and reutilization of amino acids released during the breakdown of body protein. For example, the intestinal tract lining is constantly sloughed off. The digestive tract treats sloughed cells just like food particles and absorbs their amino acids released during digestion. In fact, most protein breakdown products—amino acids—released throughout the body can be recycled and added to the pool of amino acids available for future protein synthesis. By comparing the 250 to 300 g of protein an adult makes and degrades each day with the 65 to 100 g of protein typically consumed by adults, you can see how important recycled amino acids are as a protein source for the body.3 Nonetheless, dietary protein is needed to replenish and maintain an adequate amino acid pool for protein synthesis and repair.

In typical North American diets, about 70% of dietary protein is supplied by meat, poultry, fish, milk, cheese, legumes, and nuts (Fig. 7-9).4 Worldwide, only 35% of protein comes from animal sources. Plants are the major source of protein in many areas of the world.

Figure 7-9

Food sources of protein.

Page 232

As shown in Table 7-4, plants can provide ample amounts of dietary protein in addition to providing fiber and a variety of vitamins, minerals, and phytochemicals. Unlike animal proteins, plant proteins contain no cholesterol and little saturated fat, unless added during processing. North Americans might benefit from adding soy and other plant proteins to their diets because higher intakes of these proteins may help decrease the risk of cardiovascular disease, certain cancers, obesity, and diabetes.58 In fact, the FDA has approved a health claim regarding the benefits of soy protein in lowering blood cholesterol levels.

As a way to add more plant proteins to your diet, consider these suggestions:

    • At your next cookout, try a veggie burger instead of a hamburger. These are available in the frozen foods section of the grocery store. Many restaurants have veggie burgers on their menus.

    • Sprinkle sunflower seeds or chopped walnuts on top of a salad to add taste and texture.

    • Mix chopped pecans or almonds into the batter of banana bread, muffins, or pancakes to boost your intake of monounsaturated fats and protein.

Page 233
  • Eat edamame (green soybeans) or roasted soy nuts as a snack.

  • Spread peanut butter, instead of butter or cream cheese, on bagels.

  • Consider using soy milk, especially if you have lactose intolerance. Look for varieties that are fortified with calcium.

  • Substitute black beans or vegetarian refried beans for the meat or fish in your tacos.

  • Make a stir-fry with tofu, cashew nuts, and a variety of vegetables.

Evaluation of Food Protein Quality

Scientists use various measures to evaluate the protein quality of a food. These measures indicate a food protein’s ability to support body growth and maintenance. Protein quality is determined primarily by the food’s digestibility (amount of amino acids absorbed) and amino acid composition compared with a reference protein (e.g., egg white protein) that provides the essential amino acids in amounts needed to support growth. The digestibility of animal proteins is relatively high (90–100%), in contrast to that of plant proteins (70%).

It is important to note that the concept of protein quality applies only under conditions in which protein intakes are equal to or less than the amount of protein needed to meet the requirement for essential amino acids. When protein intake exceeds this amount, the efficiency of protein use is decreased, even with the highest-quality proteins. This occurs because, once essential amino acid needs have been met, the remaining amino acids (both essential and nonessential) are mostly degraded for use as energy.

Legumes are rich sources of protein. One-half cup meets about 10% of protein needs but contributes only about 5% of energy needs.
Biological Value (BV)

The biological value (BV) of a protein is a measure of how efficiently the absorbed food protein is converted into body tissue protein. If a food possesses adequate amounts of all 9 essential amino acids, it should allow a person to efficiently incorporate amino acids from food protein into body protein.

To determine the BV, nitrogen retention in the body is compared with the nitrogen content of the food protein. More nitrogen is retained when a food’s amino acid pattern closely matches the amino acid pattern of body protein. The better the match, the higher the BV. In contrast, if the amino acid pattern in a food is quite unlike body tissue amino acid patterns, more nitrogen is excreted because many of the amino acids in the food will not be incorporated into body protein. The BV of such a food protein is low, as little of the nitrogen is retained in body tissues.

Egg white protein has a BV of 100, the highest BV of any single food protein. This means that essentially all the nitrogen absorbed from egg protein is retained and incorporated into body tissue protein. Most animal proteins have a high BV, reflecting a tissue amino acid composition similar to that of human tissues. Plants have amino acid patterns that differ greatly from those of humans. Therefore, the BV of plant proteins is usually much lower than that of animal proteins.

Protein Efficiency Ratio (PER)

Protein efficiency ratio (PER) is another method for assessing a food’s protein quality. The PER compares the amount of weight gain by a growing laboratory animal consuming a standardized amount of the protein being studied with the weight gain by an animal consuming a standardized amount of a reference protein, such as casein (milk protein). The PER of a food reflects its biological value because the weight gain and growth measured in the PER are dependent on the incorporation of food protein into body tissue. Thus, animal proteins with a high BV also yield a high PER, whereas plant proteins generally yield a lower BV and PER because they are incomplete proteins. The FDA uses the PER to set standards for the labeling of foods intended for infants.

 The concept of biological value has clinical importance whenever protein intake must be limited. This is because it is important that the small amount of protein consumed be used efficiently by the body. For example, protein intake during liver disease and kidney disease may need to be controlled to lessen the effects of the disease. In these cases, most of the protein consumed should be of high biological value, such as eggs, milk, and meat.

Page 234
Chemical Score

The protein quality of a food also can be evaluated by its chemical score. To calculate a chemical score, the amount of each essential amino acid in a gram of the food protein being tested is divided by the “ideal” amount for that amino acid in a gram of the reference protein (usually egg protein). The lowest (limiting) amino acid ratio that is calculated for the essential amino acids of the test protein is the chemical score of that protein. Chemical scores range from 0 to 1.0.

Protein Digestibility Corrected Amino Acid Score (PDCAAS)

The most widely used measure of protein quality is called the Protein Digestibility Corrected Amino Acid Score (PDCAAS). This score is derived by multiplying a food’s chemical score by its digestibility. For example, to determine the PDCAAS of wheat, multiply its chemical score (0.47) by its digestibility (0.90). This gives a PDCAAS of approximately 0.40. The highest PDCAAS is 1.0, which is the score for soy protein and most animal proteins. A protein missing any of the 9 essential amino acids (e.g., gelatin) has a PDCAAS of 0 because its chemical score is 0.

Meat, fish, a nd poultry are primary sources of high biological value protein.

For nutrition labeling purposes, protein content (when listed as % Daily Value) is reduced if the PDCAAS is less than 1.0. For example, if the protein content of ½ cup of spaghetti noodles is 3 g, only 1.2 g are counted when calculating % Daily Value, since the PDCAAS of wheat is 0.40 (3 g × 0.40 = 1.2). Other PDCAAS values are egg white, 1.0; soy protein, 0.92 to 0.99; beef, 0.92; and black beans, 0.53. Currently, the Nutrition Facts panel rarely contains the % Daily Value for protein because manufacturers do not want to spend the money needed to determine the PDCAAS.

CASE STUDY

Bethany is a college freshman. She lives in a campus residence hall and teaches aerobics in the afternoon. She eats 2 or 3 meals a day at the residence hall cafeteria and snacks between meals. Bethany decided to become a vegetarian after reading an article describing the health benefits of a vegetarian diet. Yesterday, her diet consisted of a café latte and Danish pastry for breakfast; a vegetarian tomato-rice dish, pretzels, and a diet soft drink for lunch; 2 cookies in the afternoon after aerobics class; and a vegetarian sub sandwich with 2 glasses of fruit punch for dinner. In the evening, she had a bowl of popcorn. What is missing from Bethany’s current diet? How can she improve her new diet to meet her nutrient needs? What foods would Bethany need to include in her diet to increase her protein intake?

7.7

Health Concerns Related to Protein Intake

Many people living in developing countries suffer from malnutrition and disease because dietary protein supplies are limited.10 In contrast, the residents of developed countries tend to eat more protein than they need and may boost their intake even higher by consuming protein or amino acid supplements.3 As you know, getting sufficient amounts of protein is required for good health, but getting too little or too much can have serious health consequences.1011

Protein-Energy Malnutrition

Protein deficiency rarely develops as an isolated condition. It most often occurs in combination with a deficiency of energy (and other nutrients) and results in a condition known as protein-energy malnutrition (PEM), or protein-calorie malnutrition (PCM). In many developing areas of the world where diets are often low in protein and energy, PEM is a very serious public health concern. Although PEM can affect people of all ages, its most devastating consequences are seen in children. Without adequate protein and energy, children fail to grow normally, and many develop diarrhea, infections, and diseases and die early in life. Of the 55,000 people who die of hunger each day, nearly two-thirds are children.10

PEM usually occurs as either marasmus or kwashiorkor. These conditions differ in the severity of the overall energy and protein deficit and the related clinical characteristics (Fig. 7-15). Marasmus develops slowly from a severe deficiency of energy (and, in turn, protein and micronutrients). Over time, this leads to extreme weight loss, muscle and fat loss, and growth impairment. Kwashiorkoroccurs more rapidly in response to a severe protein deficit, typically accompanied by underlying infections or disease. Kwashiorkor is characterized by edema, mild to moderate weight loss, growth impairment, and the development of a fatty liver (excess accumulation of fat in the liver).

Figure 7-15

Classification of undernutrition in children.

Page 244

PEM is most prevalent in parts of Africa, Southeast Asia, Central America, and South America.1 However, it also is seen in some population groups in industrialized countries. Those at greatest risk are individuals living in poverty and/or isolation and those with substance abuse problems, anorexia nervosa, or debilitating diseases (e.g., AIDS or cancer). Some hospitalized patients also are at increased risk of PEM because of poor prior health, low dietary intakes, and increased protein needs for recovery from surgery, trauma, and/or disease. Malnourished patients face a much greater risk of complications and even death. Consequently, hospitals have developed nutrition support teams to ensure appropriate nutritional care for at-risk patients.

Kwashiorkor

Kwashiorkor is a word from Ghana that means “the disease that the first child gets when the new child comes.” From birth, an infant in developing areas of the world is usually breastfed. Often by the time the child is 12 to 18 months old, the mother is pregnant or has already given birth again. The mother’s diet is usually so marginal that she cannot produce sufficient milk to continue breastfeeding the older child. This child’s diet then abruptly changes from nutritious human milk to starchy roots and gruels. These foods have low protein densities compared with their energy content. Additionally, the foods are usually high in plant fibers and bulk, making it difficult for the child to consume enough to meet energy needs and nearly impossible to meet protein needs. Many children in these areas also have infections and parasites that elevate protein and energy needs and often precipitate the development of kwashiorkor.

The presence of edema in a child who still has some subcutaneous fat is the hallmark of kwashiorkor (see Fig. 7-15). Other major symptoms of kwashiorkor are apathy, diarrhea, listlessness, failure to grow and gain weight, infections, and withdrawal from the environment. These symptoms also complicate other diseases that may be present. For example, measles, a disease that normally makes a healthy child ill for only a week or so, can become severely debilitating and even fatal in a child with kwashiorkor.

Many symptoms of kwashiorkor can be explained based on our knowledge of proteins. Proteins play important roles in fluid balance, growth, immune function, and the transport of other nutrients. Thus, protein deficiency can severely compromise these functions.

Page 245

If children with kwashiorkor are helped in time—infections are treated and a diet ample in protein, energy, and other essential nutrients is provided—the disease process often reverses and they begin to grow again. Unfortunately, by the time many of these children reach a hospital or care center, they already have severe infections. Thus, despite good medical care, many still die. Those who survive often continue to battle chronic infections and diseases.10

Marasmus

Marasmus is the result of chronic PEM. It is caused by diets containing minimal amounts of energy, protein, and other nutrients. The word marasmus means “to waste away.” Over time, the severe lack of energy and protein results in a “skin and bones” appearance, with little or no subcutaneous fat (see Fig. 7-15).

Marasmus usually develops in infants who either are not breastfed or have stopped breastfeeding in the early months. Often, the weaning formula used is incorrectly prepared because of unsafe water and because the parents cannot afford sufficient infant formula for the child’s needs. The latter problem may lead the parents to dilute the formula to provide more feedings, not realizing that this deprives the infant of essential calories, protein, and other nutrients.

An infant with marasmus requires large amounts of energy and protein to restore growth, development, and overall health. Unless the child receives adequate nutrition, full recovery from the disease may never occur. Most brain growth occurs between conception and the child’s first birthday. If the diet does not support brain growth during the first months of life, the brain may not fully develop, resulting in poor cognitive and intellectual growth.

Some hospitalized patients are at risk of protein-energy malnutrition (PEM) because of poor dietary intakes and increased needs for recovery from surgery, trauma, or disease.
High-Protein Diets

In addition to recommending adequate protein consumption, the Food and Nutrition Board also suggests that protein intake not exceed 35% of energy intake.3 Diets containing an excessive or disproportionate amount of protein do not provide additional health benefits. Instead, high protein intakes may increase health and disease risks. One area of concern is the effect of excess protein on the kidneys.1213 Recall that the kidneys are responsible for excreting excess nitrogen as urea. Thus, high-protein diets may overburden the kidneys’ capacity to excrete nitrogen wastes. Additionally, because water is needed to dilute and excrete urea, inadequate fluid intake can increase the risk of dehydration as the kidneys use body water to dispose of the urea. These concerns are greatest for people who already have impaired kidney function. A lower-protein diet with adequate fluid intake is recommended for these individuals to help preserve kidney health.13

When excess protein is primarily from a high intake of animal proteins, the overall diet is likely to be low in plant-based foods and consequently low in fiber, some vitamins (vitamins C and E and folate), minerals (magnesium and potassium), and beneficial phytochemicals. Animal proteins are often rich in saturated fat and cholesterol. As a result, these diets can increase the risk of cardiovascular disease.568 Diets that also contain high amounts of red meat (especially in cured forms, such as hot dogs, ham, salami, and luncheon meats) have been associated with an increased risk of certain cancers.14

High-protein diets also may increase urinary calcium loss and eventually lead to a loss of bone mass and an increased risk of osteoporosis.5 These findings are some-what controversial, however, and are less of a concern for individuals with adequate calcium intakes.

Other concerns, particularly with athletes, are the health risks associated with excess protein and amino acid supplementation. As described earlier, our bodies are designed to obtain amino acids from dietary sources of whole proteins. This assures a supply of amino acids in proportions needed for body functions and prevents amino acid toxicity, especially for methionine, cysteine, and histidine—the most toxic amino acids.11 When individual amino acid supplements are taken, chemically similar amino acids can compete for absorption, resulting in amino acid imbalances and toxicity risk.

Page 246
How big is your food print

Growing evidence indicates that what we eat may affect not only our personal health but also that of the environment. Many scientists believe that meat-rich diets and the agricultural practices that support the production of food for these diets negatively affect the environment. For instance, producing food for nonvegetarian diets (especially beef-based diets) uses more water, fossil fuel energy, fertilizer, pesticides, and acres of farmland than vegetarian diets.29Meat-rich diets also cause greater emissions of greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, which are associated with global warming.30 Scientists are concerned that continued global warming may, in turn, decrease agricultural productivity, reduce farmers’ incomes, and increase global food insecurity.31

Not all scientists agree with these findings and concerns, however. Some believe that consuming a small amount of dairy and/or meat may actually increase land use efficiency, thereby protecting environmental resources and promoting food security.32 They point out that high-quality farmland is required to grow fruits, vegetables, and grains, whereas meat and dairy products can be produced on the more widely available, lower-quality land. Even though diets containing meat use more land, they can feed more people because of the greater availability of lower-quality farmland. It appears that diets have different “agricultural land footprints,” depending on the amount of plant-based and animal-based food they contain. Supporters of mixed animal/vegetable–based diets point out that vegetarian diets often include tofu and other meat substitutes produced from soy, chickpeas, and lentils. Many meat substitutes are highly processed and require energy-intensive production methods. Thus, including small amounts of meat may offer both environmental and nutritional benefits.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s