Carbohydrates
Rank the sweetness of fructose, sucrose, glucose, lactose, and galactose.
Fructose (173) Sucrose (100) Glucose (74) Galactose (33) Lactose (16)
Explain the cause of lactose intolerance, its symptoms, identify who is likely to experience it and why, and ways to handle it.
- Caused by low levels or no lactase production, this leads to a decreased or no digestion of lactose in the small intestine, undigested lactose travels to the large intestine - Symptoms: bloating, diarrhea, gas - Likely to experience it: non-caucasians (absence of dairy in traditional food in the cultures), elderly of any ethnic group (lactase levels tend to decline with age in everyone) - Ways to handle it: eat food naturally low in lactose, eat foods that have been pretreated with lactase, eat small amounts of lactose-containing foods with other foods, lactaid drops
Explain the purpose of the glycemic index, how it is determined for an individual food, and describe its potential significance, limitations, and appropriate use.
- Created as a way to compare different foods' effects on blood glucose levels (glycemic response) - Determined for an individual food by feeding test subjects the amount of that food (at one time) that provides 50g of carbohydrate; calculated by comparing the area under the curve for the test food to the standard: (Area under the glycemic response curve for the test food)/(Area under the glycemic response curve for glucose)*100=GI - Uses: Many weight loss programs use the Glycemic Index as a basis for their plans - Limitations: We don't always eat a food by itself, we don't necessarily eat the amount of food used in the glycemic index test, the lists vary widely depending on the source of the data, significant differences in an individual food's GI based on whether you eat it hot or cold - Be aware of foods with a naturally low GI (<55), especially legumes & include them more frequently in your diet than foods with higher GIs (>70)
Describe ways to reduce discomfort (gas) associated with high-fiber vegetable and legume consumption.
- Increase fiber intake SLOWLY to give your GI tract time to adjust - DRAIN and RINSE canned beans before using - Rinse dry beans several times; do not use rinse water in cooking
Explain the history of the development of the glycemic index and list and explain the factors that can influence the rate of carbohydrate digestion and absorption.
- It was assumed that complex carbohydrates (starches) would take longer to be digested & absorbed than simple sugars because they were bigger molecules; this is not the case, the complexity of the molecule was not the most important factor in determining the rate of digestion and therefore not a good predictor of how it might affect blood glucose levels - Length of cooking time: the more the starch grains swell, the more quickly the starch is digested & therefore absorbed - Starch structure: the greater the degree of branching, the more quickly the starch is digested & therefore absorbed - Presence of fructose or galactose v. glucose: fructose & galactose must first be converted to glucose in the liver following absorption, carbohydrates containing these monosaccharides (lactose, sucrose), will produce a slower rise in blood glucose levels - Amount of soluble fiber, fat, &/or protein in the food: these all can delay stomach emptying, therefore the higher these levels re in food the less quickly its carbohydrates will reach the small intestine to be digested and absorbed
Explain why type 2 diabetes often goes unnoticed, why rates are raising in the US, and describe the potential effects of this disease.
- due to the absence of obvious outward symptoms - increase in childhood obesity - leading cause of kidney failure, non traumatic lower-limb amputations, blindness, major cause of heart disease, stroke, 7th leading cause of death
Explain the genesis of the federal enrichment program and the ways in which enriched flour is the same and different from whole wheat flour.
- grew out of concerns regarding the health of Americans during WWII - refining removes the bran & germ of the grain, which removes much of the fiber, vitamins, minerals, and phytonutrients - enriched --> adding back some of the nutrients whose levels decrease as a result of the refining process
Explain the primary function of digestible carbohydrate in the body, list the DRI for total carbohydrate consumption and for added sugars, and explain the rationale for each.
- provide energy in the form of glucose - DRI: 45-65% (carbs) - DRI: less than 25% (added sugars) Restricting added sugar is designed to restrict foods that are nutrient poor
Describe how someone can be sure that a product is truly whole grain and there issues to be aware of when evaluating a food for its fiber content.
- scan the ingredient list & look for the word "whole" in front of a grain identified first on the label's ingredient list - bread products labeled with the words "multi-grain", "stone-ground", "100% wheat", "cracked wheat", "wheat", "seven-grain", or "bran" are not whole-grain products (must specifically state "100% whole grain" - dark/brown bread does not indicate whole grain content (dark coloring can be from molasses or caramel food coloring)
Explain what high fructose corn syrup is, why food manufacturers like to use it, and whether there should be concerns about its consumption.
- starts as corn syrup (polysaccharide of glucose) - polysaccharide --> (break down) monos of glucose - take some of glucose & convert it to fructose = high fructose corn syrup It is really sweet, manufacturers do not have to add as much, cheap & readily available 55% fructose & 45% glucose: not much different than sugar (50% fructose & 50% glucose); no good evidence that HFCS is any worse than you for sugar
Describe the basic structure of starches, how they differ from one another and how that affects their characteristics, and list examples of their dietary sources.
- thickening & gel-forming characteristics Differences: - number of glucose molecules in the starch, degree of "branching" of the molecule Dietary Sources: - tuberous vegetables (sweet potato, white potato) - cereal grains (corn, wheat, rye, barley, oats) - rice - legumes (beans) - nuts, seeds
List the ways in which sugars are used in food processing.
- to provide sweetness - to provide "mouthfeel" or "bulk" - to soften other flavors - to improve texture - as a preservative (jellies, jams)
Explain what agave nectar is and whether it is preferable to other sweeteners.
Agave nectar: is made from the agave plant (large quantities of inulin: indigestible carbohydrate that is a polysaccharide of fructose); the inulin is broken into individual molecules of fructose; 55-90% fructose (as compared to 55% fructose & 45% glucose); best to not use it in large quantities
Explain how plants might use simple sugars and complex carbohydrates (why fruits are sweet and seeds are starchy).
Animals eat the fruit, disperse the seeds
Identify reasons why carbohydrate restricted diets (including Paleo) became so popular, explain why they work over the short term and whether there is evidence for their effectiveness over the long term.
Became popular: - they "work" over the short term - give you an excuse to not eat vegetables & to not work out - Worked because it's a restricted eating plan (decrease total number of calories) Evidence: - Difference in weight loss typically disappears after 1 year
Identify the 3 parts of a grain kernel, and their primary nutrient constituents.
Bran Germ Endosperm
Compare and contrast cyclamates, saccharine, aspartame, sucralose, stevia, and sugar alcohols with respect to their safety/health effects, structure, and/or stability (if applicable).
Cyclamates: banned in US, not in Canada/UK Saccharine: 300x sweeter than sugar (need little), provides 0 calories, bitter aftertaste, stable at high (cooking) temperatures, FDA attempted to ban it in the US in 1977 after some animal studies suggested it was carcinogenic (banned in Canada); public outcry brought it back, more recent studies suggest that it's safe, & an earlier requirement for a warning label has been rescinded Aspartame: 180-200x sweeter than sugar (need very little), made from phenylalanine & aspartic acid (amino acids), absorbed & metabolized but need little so contributes few total calories, not stable at high (cooking temperatures), people with PKU are born with a decreased ability to metabolize phenylalanine & have to avoid or limit their intake Sucralose: 600x sweeter than sugar, sucrose with some of the OH groups replaced with chloride atoms, poorly absorbed & what is absorbed is not metabolized so it contributes 0 calories, stable at high (cooking) temperature, overtaken aspartame as the principle artificial sweetener Stevia: 150x sweeter than sugar, sterol glycosides are extracted from the stevia plant, stable at high temperatures Sugar alcohols (sorbitol, mannitol, xylitol): used in candies, toothpaste, & other foods but also as processing aids (add texture to food, retain moisture better, prevent foods from browning), xylitol can now be purchased as a table top sweetener, they are very slowly, therefore only partially absorbed (contribute ~2.5 cal/g v. 4 cal/g), are amounts can cause diarrhea because they are slowly absorbed
Describe the structure of glycogen and how it is used by the body.
Example: Hotel - The bloodstream is a hallway in a hotel & the body's cells as the rooms behind the doors in the hallway - Insulin is the key card necessary to open the doors to allow glucose to move into the rooms from the hallway - When insulin is absent, or the doors are not responding appropriately, all or some of the glucose gets stuck in the hallway - The excess glucose must "exit" at the end of the hallway (kidneys)
Match the different types of simple sugars with their monosaccharide components (where applicable), how they are used in the body, major dietary sources and the name of the simple sugar with other name(s) that it goes by, as applicable.
Glucose: - "blood sugar", "dextrose" - used by any type of cell for energy - brain & central nervous system use glucose almost exclusively for energy (critical for normal brain & CNS functioning) - excess glucose can be converted to fat in the liver - monosaccharide: fruits, vegetables, honey - disaccharide: lactose-containing foods, sucrose-containing foods - polysaccharide: starch-containing foods, fiber-containing foods Fructose: - "fruit sugar" - some may be used for energy - some may be converted to glucose by the liver - excess fructose can be converted to fat in the liver - monosaccharide: fruits & vegetables, honey - disaccharide: sucrose-containing food - polysaccharide: fiber-containing food Galactose: - may be converted to glucose by the liver(has to) - monosaccharide: limited - part of a disaccharide: lactose-containing food Lactose - "milk sugar" - milk & products (mammalian) Sucrose - "refined sugar", "white sugar", "table sugar", "sugar" - disaccharide of glucose & fructose - fruits & vegetables
Describe the process of digesting and absorbing dietary carbohydrate and predict in what form each type of dietary carbohydrate will enter the body following digestion and absorption.
Glucose: absorbed as glucose Fructose: absorbed as fructose Galactose: absorbed as galactose Lactose: digested by lactase, absorbed glucose & galactose Sucrose: digested by sucrase, absorbed as glucose & fructose Starches: digested by amylases, absorbed as glucose *All dietary carbohydrate is absorbed in the form of monosaccharides
Define the term hyperglycemia and match the characteristics (cause and symptoms) and dietary recommendations associated with each of the two types of diabetes.
Hyperglycemia: an elevated fasting blood glucose level Type 1 Diabetes: - 5-10% of all cases - Cause: The pancreas stops producing insulin due to an autoimmune response (the body's immune system attacks its own insulin) likely due to an environmental trigger, such as a virus; genetic predisposition (linked to celiac disease); can occur at any age but most commonly develops in childhood (juvenile diabetes) - Symptoms: excessive urination, thirst (the body eliminating all excess glucose); weight loss (the body's cells are basically "starving" because glucose cannot get inside them in the absence of insulin); can have very sudden onset (days) Type 2 Diabetes: - 90-95% of all cases - Cause: the body's cells respond less well to the presence of insulin (insulin resistance); strongly associated with abdominal obesity (~80% are obese), strong genetic predisposition - Symptoms: develops gradually (outward symptoms: nighttime urination, tiredness)
Explain the carbohydrate-related components on a food label.
Includes dietary fiber & total sugars
Match the two different types of fiber with their good sources, general characteristics, and health conditions that may be prevented or ameliorated by increasing their intake, explaining gate reasons behind the health benefits as well as the potential significance, as applicable.
Insoluble Fiber: - cellulose (100% glucose) - wheat bran, whole wheat products, legumes, nuts, fruits, vegetables - does not dissolve in water - small amounts can be digested by intestinal bacteria - reduces risk of constipation & conditions associated with because fiber creates bulk in large intestine (because fiber is indigestible) which stimulates peristalsis and helps with regularity - reduces obesity: eating lots of foods that are naturally high in fiber may help with weight control because it helps fill up stomach (not digestible by our enzymes) Soluble: - gums, mucilages, pectin - sources: oat bran, oat products, legumes, fruits, vegetables - does dissolve in water, will form gels - slows the rate at which the stomach empties - larger amounts can be digested (fermented) by intestinal bacteria - prevents constipation - prevents obesity: delays stomach emptying (gel-forming characteristic), increases satiety, decreasing total # of calories - control blood glucose levels because delays stomach emptying, which delays glucose being digested & absorbed, delays glucose into blood stream - lower serum cholesterol levels because soluble fiber can bind to cholesterol & prevent absorption
Identify ways by which manufacturers can add purified fiber to foods and discuss what is, or is not known, about their healthfulness as compared to whole food fiber sources.
Inulin: polysaccharide of fructose (chicory root extract), soluble fiber, may contribute to sweetness Oligofructose: shorter chains of fructose molecules, soluble fiber Polydextrose: mixture of dextrose & other ingredients; soluble fiber Modified wheat starch: modified to make it resistant to human amylase Soy fiber Sugarcane fiber - little research on purified fiber, unknown if it hs similar effects to fiber
List the levels of fiber of intake that are recommended by the DRIs and explain why Americans are/are not close to meeting those goals.
Men: 35 g/day Women: 25 g/day The typical American consumes 10-15 g/day
Predict the potential consequences of using a cellulase supplement and explain why, and a soluble fiber supplement that binds to dietary fat and explain why.
Not beneficial: losing benefits of fiber You would take cellulose (indigestible) & break it down; increases number of calories consumed
Explain the relationship, or lack thereof, between sugar(s) and: obesity, heart disease, cancer, diabetes, tooth decay, and hyperactivity.
Obesity: no evidence that sugars cause obesity; easy to eat in large quantities (increase in total # of calories), flavored & coupled with fat Diabetes: no evidence that sugars cause diabetes; long-term intake of diets high in refined carbohydrates increase the risk of diabetes development Acne/Heart Disease/Cancer: no evidence that sugars cause acne/heart disease/cancer; diets high in refined carbohydrates (serum triglyceride levels) can increase the risk for heart disease Tooth Decay: bacteria in the mouth form plaque, plaque interacts with dietary carbohydrates, that interaction produces acid, acid causes decay Hyperactivity: energy availability does not equal activity (hyperactivitiy), "The Halloween Effect", confounders
Identify the two potential fates for glucose that isn't used immediately for energy.
Short-term energy storage: 1. Conversion to glycogen (like an animal starch; highly branched, polysaccharide of glucose molecules: 2400 total calories, 2/3 in muscle, 1/3 in liver) Function of glycogen: Muscles: energy source to be used in "fight or flight" (quick source of energy vs fat storage; does not require oxygen) Liver: energy source during time of "fasting" (overnight) Long-term energy storage: 2. Conversion to fat: in liver storage when glycogen stores are already filled
List the 2 basic classifications of carbohydrates and their members.
Simple Sugars: - Monosaccharides (glucose, fructose, galactose) - Disaccharides (lactose, sucrose) Complex Sugars: - Polysaccharides (starches, fiber: insoluble & soluble)
Explain the differences between honey and sugar (sucrose) and their implications for choosing honey instead of sugar.
Sugar: sucrose (glucose + fructose) Honey: glucose & fructose Our bodies see it as the same thing
Describe the basic structure of fiber and how it differs from starches.
cellulose (100% glucose)
Discuss the nutritional differences between and among refined white sugar and other cane sugars and molasses.
less refined sugar products are not better for you nutritionally than completely refined sugar because the cane plant from which they come is not particularly nutrient rich, you don't eat sugar in the same serving sizes that you would bread/rice turbinado sugar suggests that it might be "rich" in vitamins/minerals but does not show in the nutrition facts
Describe what can cause hypoglycemia and how to prevent it.
low blood sugar excess insulin production in response to carbohydrate intake expect blood glucose drops too rapidly and/or too low smaller, more frequent meals, each with some protein and/or fat to moderate the rise in blood glucose level
