Recap of last lecture • GM foods • Vegetarianism • Proteins • Diet analysis • Review session
#27 Outline for today • Proteins • Food additives • How to find nutrition answers on the web:
Is a High-Protein Diet Harmful? • Low in plant foods (fiber), vitamins, phytochemicals • Intake of animal protein increases risk for heart disease (high in saturated fat) • Excessive intake of red meat is linked with colon cancer • Burden on the kidney • Increased calcium loss • National Academy of Sciences recommends no more than 2 x RDA for protein
Individual Amino Acid (AA) Supplements • Supplement may cause imbalances and toxicity (especially with methionine and tyrosine) • Body is designed to handle whole proteins • Excess of one AA can hamper absorption of other AAs
Plant Protein • No cholesterol and low in saturated fat • High in (soluble) dietary fiber, phytochemicals • Lacking in one or more essential amino acid
“Soy Power” • Lowers blood cholesterol • Contains isoflavones (genistein and diadzein) • Sources: tofu, soy milk, soy flour, tempeh, miso • Recommend 2-4 servings a week • Not recommended for women WITH breast cancer (or family history)
Protein food value • Quality • Quantity • Protein conversion efficiency • Cost
Protein conversion efficiency and cost: • Animals convert plant food into animal protein with a low efficiency, i.e. they take in much more protein and energy than they produce - depending on the animal they may consume as much as 50 lb. (usually about 20 lb. for cattle) of protein for every lb. of protein they produce. (not a problem if cattle grazing on grasslands unsuited for other uses, but most beef cattle today spend much of their time in stockyards being fed corn etc.) • In fact 76% of the US protein production is used to feed livestock. 5% of this goes to feed the 100 million dogs and cats in the US! • In general legumes are the cheapest sources of protein, and meats the most expensive.
Biological Value • Measures how efficiently the absorbed food protein can be turned into body tissue • Measures protein (AA) retention Nitrogen retained Nitrogen absorbed BV = X 100
Protein Efficiency Ratio • Compares the weight gained in a growing rat after 10 days or more eating a standard amount of protein • Measures BV (protein retention) PER = Gram weight gain Gram protein consumed
Chemical Score of Protein • Amount of each essential AA in a gram of protein in the food divided by an “ideal” amount for that essential AA • The lowest AA score is the C.S. for that food Chem. Score Mg of ess. AAn per gm of protein Required mg needs of the ess. AAn per gm of protein =
Protein Digestibility Corrected AA Score (PDCAAS) • Most widely used (on food labels) • Maximum value is 1.0 (= milk, eggs, soy protein) PDCAAS = Chem. Score x (~0.9-1.0) Range of digestibility of that protein
Food additives • Intentional • Contaminants (pesticide residues, rodent debris, microorganisms) • The average American consumes more than 5 pounds of additives a year. • GRAS list
Food additives have a very long history. Salt and smoke as preservatives, sea-weed as a thickener, flavorings etc. • legitimate uses - maintain and preserve the nutritional quality of the food • “Non-legit” uses: masking an inferior food product, making food look more attractive, increasing company profits, aiding food processing, allowing convenience foods
Food additive functions • Acid or Alkaline agents • Alternative Sweeteners • Anticaking agents • Antimicrobial agents • Antioxidants • Curing and pickling agents • Antioxidants • Sweeteners • Fat replacements • Humectants • Preservatives • Emulsifying agents • Nutrient supplements • Sequestrants • Stabilizers • Flavorings • Colorants • Flavor enhancers • Leavening agents • Maturing and bleaching agents
MSG • Flavor enhancer • Often used in Chinese foods • Small percentage of people are sensitive (Chinese Restaurant Syndrome) • Experience dizziness, sweating, rapid heart rate, nausea, vomiting, high blood pressure and headaches • Symptoms appear 10-20 minutes after ingestion • Found naturally in other foods (tomato, mushroom, parmesan cheese)
Common methods of food preservation • Heat - this kills pests and microorganisms, and also denatures enzymes which are usually responsible for the spontaneous decay. • Temperature control- refrigeration or freezing; the lower temperatures slows all processes down and therefore retards the decay. • Filtration - used to remove microorganisms from liquids. • Oxygen control- its removal means that only anaerobic organisms can grow. • Control of acidity- Many microorganisms can only grow under a limited range of pH. Some foods are thus made very acid to prevent microbial growth. • Water- If the water in a food is tied up, e.g. with salt, sugar, or by dehydration or freezing, it will prevent the growth of microorganisms.
Common preservatives • Sorbic acid (sorbate)is a fatty acid (caproic acid) and is metabolized by our bodies as a fatty acid, hence we use it as a source of food and energy. • These compounds are quite safe based on feeding studies and their known metabolic routes (They inhibit a mold enzyme required for mold growth).
Common preservatives • Sodium benzoateis effective under acidic conditions in preventing growth of molds, bacteria and yeasts. • It is used in fruit juices, carbonated soft drinks, pickles, salad dressings. • It occurs naturally in many fruit and vegetables, and has been reported to be a natural metabolite in our body. All the evidence indicates it is quite safe.
Common preservatives • Sodium bisulfite and sulfur dioxide have been used since the times of the Romans to prevent the growth of bacteria, especially in beverages. • It destroys thiamin, and can restore the red color to old meat. • On the GRAS list, however, recent legislation is limiting their use (a significant number of people are allergic to sulfites - often asthmatics). • Found in salads (keeps them looking fresh), wine
Common preservatives • Sodium nitrate and nitrite; These are used in processed meats to prevent the growth of C. botulinum. They also give the meat a nice pink color. • Converts to cancer causing nitrosaminesin the stomach • Vitamin C added can reduce the formation of nitrosamine • Actual risk is low for normal people
Common preservatives • Anti-oxidants: • The most widely used are BHA and BHT. Their role is to prevent the oxidation of unsaturated fats, especially PUFA's. • Propyl gallate is often used along with BHA/BHT since the two together seem more effective.
Common preservatives • Sequesterants: These are added to complex metal ions such as iron which catalyze oxidation, or react with other components to form precipitates in beverages. EDTA is probably the most common, and many acids are also used for this purpose.
Common preservatives • Colors: • About 4 million pounds of synthetic dyes go into our US food supply each year. • Used to make foods look acceptable. • 90% are synthetic, many from coal tar, many probably carcinogenic. Among the known "baddies" Red No. 40, Citrus Red No. 2. Yellow No. 5, Blue No. 1, Orange B, Red No. 3. These are all associated with studies demonstrating them to be carcinogens in animal studies.
Natural Toxins • Occur naturally in foods • Safrole from sassafras, mace, nutmeg • Solanine from potato shoots • Mushroom toxins • Avidin in raw eggs • Thiaminase in raw clams and mussels • Tetrodotoxin in puffer fish • Oxalic acid in spinach, strawberries, etc. • Nitrites/nitrates, aflatoxin
Toxic contaminants • Heavy metals, especially lead, mercury and cadmium; dioxin, PCB's, etc. • Pesticide and herbicide residues. Hazardous ones are more likely in imported foods, from other countries where the regulations are less stringent e. g. many pesticides banned in the US are used in Mexico and the food exported to the US.
Lead Poisoning • A heavy toxic metal • Causes anemia, kidney disease, damage the nervous system, IQ deficits, behavior disorders, slowed growth • Lead from solder joints, lead paint, playground, metal containers • A high fat, low calcium, low iron diet absorbs more lead • Thus, a low fat, adequate calcium and iron diet is recommended
Mercury • From large predator fish (shark, sword fish) • Accumulates mercury in the fish • These fish are tested more frequently for mercury level • Not recommended for women of childbearing years • Birth defects are common
Dioxin • Cancer causing, damaging to reproduction, development, and immune system • From trash burning • From bottom feeding Great Lakes fish • Exposure seen in people who consume locally caught fish, intake of animal fats
Urethane • From fermentation of alcohol • Increase upon heating (of the alcohol) • Causes cancer in animal studies
Polychlorinated Biphenyls (PCBs) • Used in industrial products • Linked to liver tumors and reproductive problems in animals • Still found in freshwater fish • Limit established for uses by FDA
How to Reduce Your Exposure to Toxins • Know what foods pose a risk • Practice moderation and variety • Trim fat from meat and fish • Wash fruits, vegetables thoroughly • Cook meat thoroughly
Perspective • Smoking kills 150,000 people a year from lung cancer; • Alcohol kills 100,000, • Motor vehicles 50,000. • Drunk drivers kill an average of 70 people a day! • A few people die each year from food poisoning - either bacterial or toxins (e. g. mushrooms, shellfish). • Definite deaths from food additives and pesticide residues have not been documented, at least to any extent in the US. • Thousands die from microbial food poisoning