Lecture 55 Flashcards
What is a Recommended Dietary Allowance (RDA) or Dietary Reference Intake (RDI)?
An estimate of the amount of a nutrient required to meet the needs of 97-98% of the U.S. population
What is the RDA influenced by?
1) Age
2) Sex
3) Pregnancy
4) Lactation
5) Injury
6) Illness
What is the recommended dietary composition?
Protein: 12% of calories
Fat: 15-30% of calories
Carbohydrates: 58-73% of calories
What is the daily caloric requirement for the average person?
The daily caloric requirement for a 70kg (154 lb) moderately active person is about 2700 kcal and for a 50 kg (110 lb) person is about 2000 kcal
What three components should be considered for energy requirements?
1) Basal Metabolic Rate (BMR) is about 1800 kcal for a 70 kg individual and about 1300 kcal for a 50 kg person
2) The thermic effect of food associated with digestion involves about 5-10% of the total caloric requirement
3) Physical activity for a sedentary individual will require 30-50% above the BMR while a highly active individual may require 100% above the BMR
Note: Caloric restriction usually extends the life of experimental animals
How is Body Mass Index calculated?
Body Mass Index = Weight in kg/height in meters squared
1) A BMI over 25 is regarded as overweight
2) A BMI over 30 is regarded as obese
Describe the energy yield of macronutrients
1) The energy provided by the macronutrients is greater for fat (9 kcal/gram) than for protein and carbohydrate (4 kcal/gram)
2) Alcohol should not be a macronutrient but its energy yield is intermediate (7 kcal/gram)
Describe characteristics of fat
1) Note the dietary essential fatty acids include linoleic acid and linolenic acid
2) Foods differ in their content of saturated monounsaturated and polyunsaturated fatty acids
3) Partially hydrogenated vegetable oils such as margarine have some trans unsaturated fatty acids. Trans unsaturated fatty acids resemble saturated fatty acids in their physical properties and their impact on the cardiovascular system
4) Animal fat in addition to being usually more saturated than plant lipids also contains cholesterol
Describe characteristics of carbohydrates
1) Carbohydrates are not essential in teh diet but are beneficial. Digestion is more rapid for monosaccharides and disaccharides than for polysaccharides. Consumption of sucrose should be limited
2) Most fiber consists of polysaccharides that are not substrates for mammalian enzymes e.g. cellulose and pectin but not lignin
3) Impaired ability to use carbohydrates in diabetes mellitus results in a metabolic pattern that resembles some of the changes seen in starvation
Describe characteristics of protein
1) Proteins are not required as such but the diet must contain the dietary essential amino acids (mnemonic: PVT TIM HALL). The omission of an essential amino acid results in a negative nitrogen balance. Carbodhydrate in the diet has a protein-sparing effect
2) The biological value is usually greater for animal than for plant proteins but gelatin derived from collagen has a low value due to its limited amino acid composition. The protein RDA for adults is 0.8 g/kg body weight or 56g for a 70kg individual
What are examples of micronutrients and RDAs?
1) Vitamins (organic micronutrients) & choline
2) Minerals:
Potassium: 2-5g
Sodium: 1-3g
Chloride: 1.7 - 5.1g
Calcium: 1000mg
Phosphorus: 700mg
Magnesium: 350mg
Iron: 8mg (male), 18mg (female)
Zinc: 10mg
Manganese: 2-5mg
Fluoride: 3-4mg
Copper: 900 micrograms
Chromium: 50-200 micrograms
Iodine: 150 micrograms
Molybdenum, selenium, cobalt < 100 micrograms
Describe characteristics of fiber
1) The term fiber is used to describe nondigestible polymers including lignin and several polysaccharides (cellulose, hemicellulose, pentosans, & pectin)
2) Dietary fiber increases bowel motility. Fiber may bind toxins & decrease diverticulosis & colon cancer. However, fiber may bind trace elements and decrease teh absorbance of fat-soluble vitamins
What is the relationship between glycemic index and low carbohydrate diets?
1) Some diets, notably the Atkins & South Beach diets, recommend a low carbohydrate diet with higher amounts of fat and protein than traditionally recommended. The rationale for these diets is that high fat and protein diets induce satiation more rapidly than high carbohydrate diets. Two studies published in 2003 indicated that low carbohydrate diets are at least as effective as low calorie, high-carbohydrate diets in achieving weight loss in obese subjects
2) The glycemic index measure the relative effect on blood glucose levels compared with glucose which is given a value of 100. Some nutritionists consider that foods with a high glycemic index should be avoided
3) The relative long term effects of high and low carbohydrate diets on blood lipids and cardiovascular health remain to be established
Are dietary supplements safe or efficient?
1) Under the Dietary Supplement Health and Education Act of 1994 (DSHEA), dietary supplements do not have to be proved safe or efficacious. The FDA can only ban them if it can prove that thy pose a “significant and unreasonable risk”
2) It took the FDA 10 years to ban ephedra as a dietary supplement
3) Supplement manufacturers cannot make health claims without rigorous testing and approval of the FDA, but they can make claims that are health related e.g. supplement X promotes a healthy liver
4) Toxicity concerns have been raised about aristolochia, yohimbe, chapparal, comfrey, germander, kava, & bitter orange
What are examples of artificial sweeteners?
The following low calorie materials are used as artificial sweeteners:
1) Saccharin (Sweet’N Low)
2) Aspartame (NutraSweet) and Neotame. Aspartame should be avoided by individuals with phenylketonuria and yield a small amount of formaldehyde from methanol
3) Sucralose (Splenda) is a chlorinated sucrose molecule
4) Acesulfame potassium
5) Sorbital is metabolized more slowly than sucrose
