Plants, food and human health: You are what you eat? (TTPB21) Teaching Guide

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1 Plants, food and human health: You are what you eat? (TTPB21) Teaching Guide Overview We need food to survive, and plants are an important part of any human diet. Changes to our diet, brought about by the development of agriculture and industrial food processing, have had both positive and negative effects on human health globally. While many people suffer from chronic hunger and malnutrition, currently more humans in the world suffer the ill-effects of eating too much overall, and with a poor nutritional balance i.e. too much of the wrong kinds of foods, and not enough of the right kinds. This lecture describes the chemical composition of food, how different foods affect us physiologically and can contribute to the prevention or development of chronic diseases, and how nutrition research, agricultural practices and plant breeding programs can contribute to more healthful diets. Learning objectives By the end of this lecture the student should be able to: Compare and contrast the different types of nutrients found in food Evaluate the strengths and weaknesses of different types of nutritional studies Identify four human health issues strongly correlated with diet Summarize risk factors associated with the development of type 2 diabetes Summarize risk factors associated with the development of cardiovascular disease Evaluate sources of nutritional information and their recommendations Appraise his or her own diet in comparison to recommended dietary guidelines Summarize the roles of plant science in improving human nutrition Study / exam questions (understanding and comprehension) True or False most Americans and Europeans eat at least five servings of fruit or vegetables every day Describe the relationship between glucose, sugars, starches and carbohydrates Explain what is meant by dietary fiber, and give examples of the two types Identify eight sources of dietary protein Describe the structure of saturated and unsaturated fatty acids, trans fats, and omega-3 and omega-6 fatty acids What is the connection between provitamin A and vision? In what fundamental way do minerals differ from vitamins and phytonutrients? Define bioavailability and explain it in the context of mineral assimilation Give two examples of phytonutrients and their health effects What is the gut microbiota and how does it affect nutrient assimilation? What are the strengths and weaknesses of the major types of nutritional study? True or False Dietary deficiencies are only a problem in the developing world True or False - Chronic diseases kill more than twice as many people as infectious diseases including HIV/AIDS How does insulin control blood glucose levels? How do type 1 and type 2 diabetes affect blood glucose levels? What is the connection between low density lipoproteins, oxidative stress, inflammation and cardiovascular disease? The contribution of diet to the onset and progression of cancer is less than for other chronic diseases. Why do you think this is the case? Why is it more difficult to study the connection between diet and cancer as compared to other chronic diseases? How does your diet compare to the recommendations from the World Cancer Research Fund, the US Depart of Health and Human Services, and other guidelines 1

2 included here? Do you think that learning more about the connection between food and health might affect your food choices? If so, how? If not, why not? Discussion questions (engagement and connections) What obstacles prevent people from eating five or more servings of fruits and vegetables every day? How could governments and public agencies help to remove these obstacles? How important do you think it is for governments to invest money into promoting more healthful dietary habits, and why? What foods are fortified and why? Investigate the history of food fortification where you live. Who regulates and mandates fortification practices? How is public opinion factored into these policies? Do you think food fortification practices should be expanded? Packaged foods are labelled with nutritional information. How precise is that information? In what ways might the nutritional content vary from package to package, and consumer to consumer? The development of improved sequencing technologies has allowed scientists to explore the microbial compositions of oceans, soils and the human intestine! What are some of the findings these metagenomic surveys of the human intestinal microbiota have revealed? (A quick search will provide you with several current review and research articles). What is the feasibility of using this knowledge to promote health can you envision an application of this information? How well are the physiological changes associated with the onset of type 2 diabetes understood? What is metformin and how is it used in the treatment of type 2 diabetes? What other pharmacological options are available? How reversible is the condition? Statins are amongst the most frequently prescribed drugs. What are statins and what do they do? Imagine that you have only a basic background in science, and you have just learned that you have a chronic disease. Spend 30 minutes using the internet to try to learn more about this disease and its treatments. Keep a tally of how many total websites you visit, how many try to sell you a book and / or pill, supplement or meal plan to help you manage or treat the disease, how many are news stories that do or do not cite or link to peer-reviewed articles, and how many are from not-for profit or governmental organizations that offer what you judge to be sound advice. Rank each site from 1 to 5, with 1 being dangerous or rip off and 5 being excellent, clear, valuable free advice. How accessible is scientifically sound information about food and health, and how easy would it be for the average person to discriminate health from hoax? What are some of the ways that plant scientists help reduce the incidence of chronic disease? If you were on a funding agency panel, which kinds of projects would you give top priority to? How does the use of genetic modification (GM) affect your choices; would you be more likely to support a project like provitamin-a enriched cassava, that does not use GM, than golden rice, that does? If GM plays into your decision-making, why? 2

3 Lecture synopsis INTRODUCTION (1-6) Food plays a major role in human health, but food intake isn t always optimal for growth. In some cases this is because nutritious food is too expensive or unavailable. In others the reasons for unhealthy eating are more complex. Our food choices are determined by lots of factors, including emotional, economic and the influence of advertising. The expression You are what you eat is only partly true the food consumed is processed differently in different people, based on factors including metabolic rates and intestinal bacteria. This lecture looks at the relationship between plants, food, and human health by examining the components of food, and how food and nutrition affect health. WHAT WE GET FROM FOOD (7 43) The chemical composition of food can be described as macronutrients (carbohydrates, fats and protein, as well as fiber), micronutrients (vitamins, minerals) and phytonutrients (compounds with other health-promoting functions). Macronutrients Carbohydrates (8 14) Carbohydrates (C-H 2 O) are sugars, and also starches, which are polymers of sugars. Carbohydrates are energy sources rapidly metabolized to produce energy, but also stored when energy is in abundance. Some plant carbohydrates are soluble or insoluble fibers. Some are fermented by intestinal bacteria and contribute to bowel health, whereas some are not metabolized. Dietary fibers are generally considered beneficial. Proteins (15 17) Proteins are polymers of amino acids, which can be broken down as energy sources but also used as building blocks for protein synthesis. Animal and plant foods can be good sources of protein. Lipids fats and oils (18 25) Lipids (hydrocarbons) are energy-rich molecules, building blocks for cell membranes, and precursors for other molecules. The degree of saturation of the fatty acids affects their properties; saturated fatty acids have a higher melting point than unsaturated fatty acids (and therefore are more likely to be solid at room temperature). Most trans fatty acids are produced industrially, and have been correlated with health risks. Some omega-3 (n-3) fatty acids (indicating a double bond three carbons in from the end) and omega-6 (n-6) fatty acids cannot be produced in our bodies and must be ingested. A high dietary ratio between n-3 and n-6 fatty acids is considered beneficial. Micronutrients Vitamins (26 27) There are 13 recognized vitamins that must be ingested for optimal health; however, overingestion of some vitamins can be as detrimental as under-ingestion of them. Healthy people can meet their needs for most vitamins through diet alone; however, given that many vitamins are only present in significant amounts in fruits and vegetables, this assumes a diet rich in fruits and vegetables. Minerals (28 30) Minerals are elements. Plants and animals do not synthetize minerals. Plants take them up from the soil, and animals get them through their diet. In those with limited diets, or that consume foods grown on depleted soils, mineral deficiencies can occur, particularly iron. Mineral nutrition is also affected by the bioavailability of the mineral; some compounds can enhance the uptake of minerals from food, and others can limit it. Phytonutrients (31 37) Plants produce thousands of secondary metabolites, some of which can have beneficial effects on human health and are referred to as phytonutrients. Although phytonutrients have not been shown to be essential for human health in the same way that vitamins and minerals are, they may be important for long-term human health. Polyphenols include anthocyanins, 3

4 flavonoids and related compounds, and some are found in green tea, soybeans and red pigmented fruits. Carotenoids include provitamin A but also lycopene, lutein and zeaxanthin, found in tomatoes, corn and some other yellow or orange fruits. Garlic and onion produce allyl sulfides, and cruciferous vegetables like broccoli and cabbage produce glucosinolates that are transformed into isothiocyanates like sulforaphane. Studies to identify phytonutrients and characterize their effects on health are ongoing, as are discussions about how their health benefits can be labelled. Intestinal bacteria (38 42) Uptake of compounds from food into the bloodstream of the consumer is a complex process with many variables, one of which is the composition of the intestinal bacteria. These diverse bacteria metabolize nutrients with various effects to the host. Some are more efficient than others in extracting energy from food, and in mice can be correlated with weight gain. HOW NUTRITION RESEARCH IS CONDUCTED (44 48) There are several types of studies used to identify the effect of certain foods on health. Some involve collecting data from large populations through surveys, either before or after health problems have been identified. Others involve experimental studies of cells, animal models, or humans. Establishing evidence that a food or compound has a true benefit on human health is very difficult and involves many types of studies. HOW DIET AFFECTS HUMAN HEALTH (49 87) Dietary deficiencies (50 56) More than one billion people are chronically hungry, and more than two billion people do not get adequate vitamins or minerals in their diet. Malnutrition disproportionally affects children, and is aggravated by crop failures, war and conflict, and poverty. Vitamin A deficiency is widespread and is a leading cause of infections and blindness. Malnutrition occurs in the developed world as well. In the early 20 th century, many foods including flour, milk and margarine and salt began to be fortified. Biofortification involves breeding or growing plants for better nutritional qualities. Diet as a factor in chronic diseases (57 86) Chronic diseases kill more than twice as many people as infectious diseases including HIV/AIDS. Diet is a factor in cardiovascular disease, type 2 diabetes and some cancers. Metabolic syndrome (60 64) Metabolic syndrome defines a set of related health conditions that predispose people to further health problems. Although not a disease per se, it is a syndrome strongly correlated with the onset of future health problems, and a useful way to describe a constellation of related, causal, metabolic risk factors. Metabolic syndrome has genetic and environmental components, and it can be avoided by maintaining a healthy body weight, by physical activity, and by not smoking. Type 2 Diabetes (65 69) Diabetes is two main diseases. Type 1 diabetes (approximately 10% of cases) is an autoimmune disease with a large genetic contribution, in which the body destroys the pancreatic insulin-producing cells and so causes a loss of insulin production. Type 2 diabetes is largely the result, in genetically susceptible individuals, of body fat accumulation and physical inactivity and the associated development of insulin resistance. The rising incidence of childhood obesity and its accompanying increased risk for the development of type 2 diabetes is a significant public health concern. Cardiovascular disease (70 81) Cardiovascular diseases (CVD) including stroke, heart attack, atherosclerosis and high blood pressure are the leading causes of death globally and account for 30% of all deaths. Blood lipid levels and forms are important indicators for the risk of CVD and metabolic syndrome, which is contributed to by high levels of serum triglycerides and low levels of high density lipoprotein (HDL) cholesterol. Low density lipoprotein (LDL) cholesterol helps remove 4

5 excess cholesterol from the body. HDL can be oxidized by reactive oxygen species, leading to their adherence to arterial walls, inflammation and plaque formation. Plaques can break off to form clots that cause heart attacks and strokes. Trans fats and saturated fats contribute to inflammation and plaque formation. Diets rich in fruits and vegetables reduce the risk of CVD, although the mechanisms remain uncertain. Cancer (82 85) Because cancers typically develop asymptomatically over many years, it is more difficult to examine the role of diet in cancer incidence and progression than in other chronic diseases. Some phytonutrients appear to play a protective role against cancer. MEDIA AND MARKETING (87 95) Many consumers get their nutritional information from newspapers, magazines and the internet, and three-quarters of those surveyed indicated that their healthy eating goals were confounded by too much conflicting information about which foods are healthy and which are not. Sensible health information is widely, freely available from health-oriented charities and public health and nutrition organizations. The advice from these organizations is surprisingly simple and includes recommendations to eat whole grains and plenty of varied vegetables. Or as summarized eloquently by Michael Pollan, Eat food, not too much, mostly plants. HOW CAN SCIENTISTS PROMOTE GOOD NUTRITION? (96 107) Scientists can promote nutrition education, but also contribute to discussions about the role of government in supporting healthy eating. Scientists can also work towards lowering the costs of fruits and vegetables by increasing their yields and shelf-lives. Biofortification efforts can improve the nutritional content of foods, especially staple crops for those whose dietary diversity is limited. SUMMARY ( ) The long-term consequences of nutritional ignorance and over-nourishment are as much a threat to human productivity as are the consequences of undernourishment, and both are unnecessary. Malnutrition and chronic diseases can be decreased through scientific and social / political tactics. 5

6 Slide Concepts Slides Table of contents - concepts 1-3 Introduction. Why do we eat what we eat? Physiological, sensorial, social, emotional, economic reasons, and the influence of media and marketing 4 There are three parts to nutritional status What you eat, what you are, and what you do 5-6 Lecture Outline, What is food? 7 What we get from food 8-14 Macronutrients carbohydrates Carbohydrates (C-H 2 O) are sugars, starches and cellulose (polymers of sugars) and used primarily for energy production. Some are readily digestible; others not. Carbohydrates accumulated to excess can be stored as glycogen or fat. Sugars fuel plant and animal cells by production of ATP in the mitochondria. Dietary fibers are soluble or insoluble and promote good health. Some natural sweeteners are low-calorie food additives Macronutrients proteins Proteins are polymers of amino acids. Digestion releases amino acids, some of which are reassembled to produce new proteins, others of which are broken down for energy production. Muscle meat, milk and eggs are protein-rich foods, as are seeds of many plants (particularly legumes). Diets very high in protein at the expense of carbohydrate can damage the kidneys which are involved in the excretion of the amino acid degradation products Macronutrients lipids (fats and oils) Lipids are hydrocarbons (C-H 2 ). Lipids are often consumed as triglycerides, made up of a glycerol attached to three fatty acids. The length and level of saturation of the fatty acids affects their physical properties as well as their effects on health. Saturated fatty acids are commonly found in animal-derived foods, and are often solids at room temperature (e.g. lard, butter). Plant-derived lipids are often unsaturated to some extent and liquids at room temperature (e.g. corn oil, olive oil). Trans fats are produced industrially and have adverse health effects Omega-3 (n-3) and omega-6 (n-6) fatty acids have a special role in nutrition because some humans are unable to synthesize some of them, so they must be ingested, particularly the n-6 fatty acid linoleic acid (LA) and the n-3 fatty acid alpha-linolenic acid (ALA). Both are precursors for the production of eicosanoids (signaling molecules). Those derived from n-6 fatty acids tend to be inflammatory, those from n-3 are anti-inflammatory, so a high dietary ratio between n-3 and n-6 fatty acids is particularly beneficial Micronutrients vitamins Vitamins are essential small nutrients that humans cannot synthesize and must be ingested in the diet. Currently there are 13 vitamins, but some occur in more than one form, and the list of what is and is not a vitamin is subject to change. Although healthy people should be able to meet their vitamin needs through diet alone, many are abundant only in fruits and vegetables. When ingested to excess, many vitamins have detrimental or toxic effects Micronutrients minerals Several dietary minerals are essential for human health, including potassium, calcium, zinc, selenium and iron. As elements, minerals are not synthesized in plants or animals. So human nutrition depends on plants taking up adequate minerals from the soil. Bioavailability is an important factor because several compounds affect how efficiently minerals are assimilated from the diet Micronutrients phytonutrients Phytonutrients are a collection of compounds, many of which are secondary metabolites of plants that have roles in defense or interactions with pollinators. 6

7 Unlike primary metabolites, secondary metabolites are often found only in a small number of species. One class of phytonutrients are the polyphenols: anthocyanins, flavonoids and related compounds. Another is the carotenoids, and another is the sulfur-containing allyl sulphides and isothiocyanates. Because the beneficial roles of these compounds have been recognized only recently, confirmation of their properties is ongoing. 37 The term functional food is imprecisely defined, but generally refers to food whose benefits go beyond traditional nutrients and vitamins. Such health claims are stringently regulated Intestinal bacteria are an important part of nutrition Food or nutrients that reach the gut can be further metabolized by intestinal bacteria. Large-scale sequencing technologies mean that it is now possible to identify the population of bacteria in the gut, and compare these populations between individuals and over time. These bacteria not only affect the energy extracted and assimilated from foods, but also can produce new compounds from the ingested food. 42 Assimilation of nutrients from food is a complex process How food is assimilated is variable and includes how food is grown, processed, macerated and digested in the mouth, stomach and intestine, and the presence or absence of other foods and microbes. 43 Summary what we get from food fuel, building blocks and essential nutrients and bioactive agents How nutrition research is conducted human volunteers are essential! 45 An early experiment James Lind s studies of scurvy 46 Types of human nutritional studies 47 Questionnaire-based studies are augmented by lab studies 48 Summary how can we understand results from nutritional studies? How diet affects human health Dietary deficiencies More than two billion people do not get adequate vitamins or minerals in their diet, mainly in the developing world but malnourishment is associated with poverty in the developed world as well. Fortification of foods (e.g. flour, milk, margarine) has helped to alleviate malnourishment in some places. Biofortification refers to breeding or growing plants for better nutritional qualities Chronic diseases are a leading cause of death, affect all income levels, and there is a strong connection between diet and chronic disease Metabolic syndrome is a set of related health conditions that predispose people to further health problems. One of the major components is a larger-thanexpected waist circumference, which reflects not only fat accumulation but also fat distribution. Abdominal fat produces harmful inflammatory cytokines that contribute to the development of chronic diseases such as type 2 diabetes and cardiovascular disease Type 2 diabetes (is different than type 1 diabetes and) is associated with insulin resistance, as is largely a result of diet, lack of exercise, and obesity. The number of cases of type 2 diabetes is increasing rapidly, even amongst children, and is a major public health concern. Both metabolic syndrome and type 2 diabetes are preventable and reversible Cardiovascular diseases (CVDs) are the leading cause of death worldwide. CVDs include stroke, heart attack, atherosclerosis and high blood pressure. Blood plasma lipid levels including high levels of triglycerides are major contributors to CVDs. Cholesterol moves through the blood as LDLs and HDLs, and a high level of LDLs is particularly harmful, as these are subject to oxidation and contribute to the formation of atheroma plaque, high blood pressure and 7

8 clots. Diet contributes to CVDs, with diets high in trans fats and saturated fats promoting it, and diets high in fruits and vegetables protecting against it Cancer The role of diet in cancer development is slightly less than CVDs or type 2 diabetes, but there is a real effect. Some phytonutrients can detoxify or interfere with potential carcinogenic chemicals and induce the expression of enzymes that detoxify them. Obesity is also correlated with a higher incidence of cancer. 86 How diet affects health summary. We have two effects nutrient deprivation, mainly as a consequence of poverty, and overconsumption and chronic diseases since 2005 more people in the world are suffering from overweight rather than underweight conditions Media and marketing muddy our impressions of healthy eating Many popular media outlets are quick to report on nutritional studies but inadequate in their interpretation of the studies. Consumers complain about too much conflicting information about which foods are healthy and which are not Selling the promise of health and weight management is a multi-billion dollar business, and the Internet is replete with self-professed health experts selling empty promises and quick health fixes. 90 Portion sizes are getting bigger sensible labelling schemes should be enforced for all food providers and made available Sensible information is available and free 96 How can scientists promote health and good nutrition? Basic research to make healthy food available and affordable Promote education about health and nutrition Contribute to discussions about government s roles Basic research can make healthy foods more affordable and accessible Scientists can work towards producing more nutritious foods - examples include increased vitamin A content, phytonutrients such as anthocyanins and precursors of isothiocyanates, precursors of long chain polyunsaturated fatty acids, and mineral nutrients Conclusions and challenges The agricultural revolution and subsequent social changes have increased our life expectancy consistently, but now those gains are threatened by chronic diseases of overconsumption. After many years of efforts to ensure that the quantity of food available to everyone is adequate, it is the time to begin to focus on the quality of that food. 8