NUTRITION IN HEALTH AND DISEASE

What we eat has an enormous impact on how healthy we are now and how likely we are to develop chronic diseases such as heart disease, obesity, and diabetes. Consuming either too much or too little of one or more nutrients or energy will result in malnutrition. Malnutrition can affect your health not just today but 20, 30, or 40 years from now. The impact of your diet on your health is also affected by your genetic background.

UNDERNUTRITION AND OVERNUTRITION

Undernutrition occurs when intake doesn’t meet the body’s needs. The more severe the deficiency, the more dramatic the symptoms. Some nutrient deficiencies occur quickly. Dehydration, a deficiency of water, can cause symptoms in a matter of hours. Drinking water can relieve the headache, fatigue, and dizziness caused by dehydration almost as rapidly as these symptoms appeared. Other nutritional deficiencies may take much longer to become evident. Symptoms of scurvy, a disease caused by a deficiency in vitamin C, appear after months of deficient intake; osteoporosis, a condition in which the bones become weak and break easily, occurs after years of consuming a calcium-deficient diet.
We typically think of malnutrition as undernutrition, but overnutrition, an excess intake of calories or nutrients, is also a concern. An overdose of iron can cause liver failure, for example, and too much vitamin B6 can cause nerve damage. These nutrient toxicities usually result from taking large doses of vitamin and mineral supplements because foods generally do not contain high enough concentrations of nutrients to be toxic. However, chronic overconsumption of calories and certain nutrients from foods can cause health problems.
The typical U.S. diet, which provides more calories than we need, has resulted in an epidemic of obesity in which more than 65% of adults are overweight or obese. Diets that are high in sodium contribute to high blood pressure; an excess intake of saturated fat and cholesterol contribute to heart disease; and a dietary pattern that is high in red meat and saturated fat and low in fruits, vegetables, and fiber may increase the risk of colon cancer. It has been estimated that over 16% of all deaths in the United States can be attributed to poor diet and sedentary lifestyle.

DIET-GENE INTERACTIONS

Diet affects your health, but diet alone does not determine whether you will develop a particular disease. Each of us inherits a unique combination of genes. Some of these genes affect your risk of developing chronic diseases such as heart disease, cancer, high blood pressure, and diabetes, but their impact is affected by what you eat. Your genetic makeup determines the impact a certain nutrient will have on you. For example, some people inherit a combination of genes that results in a tendency to have high blood pressure.
When these individuals consume even an average amount of sodium, their blood pressure increases. Others inherit genes that allow them to consume more sodium without much of a rise in blood pressure. Those whose genes dictate a significant rise in blood pressure with a high-sodium diet can reduce their blood pressure, and the complications associated with high blood pressure, by eating a diet that is low in sodium. Our increasing understanding of human genetics has given rise to the discipline of nutritional genomics or nutrigenomics, which explores the interaction between genetic variation and nutrition.
This research has led to the development of the concept of “personalized nutrition,” the idea that a diet based on the genes an individual has inherited can be used to prevent, moderate, or cure chronic disease. Although today we do not know enough to take a sample of your DNA and use it to tell you what to eat to optimize your health, we do know that certain dietary patterns can reduce the risk of many chronic diseases.

CHOOSING A HEALTHY DIET

A healthy diet is one that provides the right number of calories to keep your weight in the desirable range; the proper balance of carbohydrates, proteins, and fat; plenty of water; and sufficient but not excessive amounts of vitamins and minerals. Such a healthy diet is rich in whole grains, fruits, and vegetables; high in fiber; moderate in fat, sugar, and sodium; and low in unhealthy fats (saturated fat, cholesterol, and trans fat). In short, a healthy diet is based on variety, balance, and moderation.

EAT A VARIETY OF FOODS

In nutrition, choosing a variety of foods is important because no single food can provide all the nutrients the body needs for optimal health. Variety means choosing foods from different food groups—vegetables, grains, fruits, dairy products, and meats and beans. Some of these foods are rich in vitamins and phytochemicals, others are rich in protein and minerals, and all are important. Variety also means choosing diverse foods from within each food group. Different vegetables provide different nutrients. Potatoes, for example, are the only vegetable in many Americans’ diets. Potatoes provide vitamin C but are low in vitamin A. If potatoes are your only vegetable, it is unlikely that you will meet your nutrient needs.
If instead you have a salad, potatoes, and broccoli, you will be getting plenty of vitamins C and A as well as many other vitamins and minerals. Making varied choices both from the different food groups and from within each food group is also important because nutrients and other food components interact. Such interactions may be positive, enhancing nutrient utilization, or negative, inhibiting nutrient availability. Variety averages out these interactions. Variety involves choosing different foods not only each day but also each week and throughout the year. If you had apples and grapes today, have blueberries and cantaloupe tomorrow. If you can’t find tomatoes in the winter, replace them with a winter vegetable such as squash.

BALANCE YOUR CHOICES

Choosing a healthy diet is a balancing act. Healthy eating doesn’t mean giving up your favorite foods. There is no such thing as a good food or a bad food—only healthy diets and unhealthy diets. Any food can be part of a healthy diet, as long as your diet throughout the day or week provides enough of all the nutrients you need without excesses of any. When you choose a food that is lacking in fiber, for example, balance it with one that provides lots of fiber. When you choose a food that is very high in fat, balance that choice with a low-fat one. A balanced diet also balances the calories you take in with the calories you use up in your daily activities so that your body weight stays in the healthy range.

PRACTICE MODERATION

Moderation means not overdoing it— watching portion sizes and passing up the super sizes. Moderation means not having too many calories, too much fat, too much sugar, too much salt, or too much alcohol. Choosing moderately will help you maintain a healthy weight and prevent some of the chronic diseases, such as heart disease and cancer, that are on the rise in the U.S. population. The fact that more than 65% of adult Americans are overweight demonstrates that we have not been practicing moderation when it comes to calorie intake. Moderation makes it easier to balance your diet and allows you to enjoy a greater variety of foods.

EVALUATING NUTRITION INFORMATION

We are bombarded with nutrition information almost every day. The evening news, the morning papers, and the World Wide Web continually offer us tantalizing tidbits of nutrition advice. Food and nutrition information that used to take professionals years to disseminate now travels with lightning speed, reaching millions of people within hours or days. Much of this information is reliable, but some can be misleading. In order to choose a healthy diet, we need to be able to sort out the useful material in this flood of information.

THE SCIENCE BEHIND NUTRITION

Like all other sciences, the science of nutrition is constantly evolving. As new discoveries provide clues to the right combination of nutrients needed for optimal health, new nutritional principles and recommendations are developed. Sometimes established beliefs and concepts give way to new information. Understanding the process of science can help consumers understand the nutrition information they encounter.
The systematic, unbiased approach that allows any science to acquire new knowledge and correct and The scientific method involves making observations of natural events, formulating hypotheses to explain these events, designing and performing experiments to test these hypotheses, and developing theories that explain the observed phenomenon based on the results. In nutrition, the scientific method is used to develop nutrient recommendations, understand the functions of nutrients, and learn about the role of nutrition in promoting health and preventing disease.

HOW SCIENTISTS STUDY NUTRITION

Many different types of experiments are used to expand our knowledge of nutrition. Some make observations about relationships between diet and health; these are based on the science of epidemiology. Other types of experiments evaluate the affect of a particular dietary change on health. Some of these experiments study humans, others use animals; some look at whole populations, others study just a few individuals, and some use just cells or molecules. For any nutrition study to provide reliable information, it must collect quantifiable data from the right experimental population, use proper experimental controls, and be interpreted accurately.
Reliable data can be quantified, meaning that they include parameters that can be measured reliably and repeatedly, such as body weight or blood pressure. Individual testimonies or opinions alone are not quantifiable objective measures. For an experiment to answer the right question, scientists must study the appropriate group of people and include enough subjects. For example, if a dietary supplement claims to increase bone strength in older women, it must be tested in older women and include enough subjects to demonstrate that the supplement causes the effect to occur more frequently than it would by chance. The number of subjects needed depends on what is being studied. Fewer subjects are needed to demonstrate an effect that rarely occurs by chance.
For example, if only one man in a million can increase his muscle mass by weight training for four weeks, then an experiment to test whether a supplement increases muscle mass in men who weight train for four weeks would require only a few subjects to demonstrate an effect. If many men can increase muscle mass by weight training for four weeks, then more experimental subjects would be needed to demonstrate that the increase in muscle mass was due to the supplement rather than the weight training alone.
In order to know whether what is being tested has an effect, one must compare it with something. A control group acts as a standard of comparison for the factor, or variable, being studied. A control group is treated in the same way as the experimental group except that the control group does not receive the treatment being tested. For example, in a study examining the effect of a dietary supplement on muscle strength, the control group would consist of individuals of similar age, gender, and ability, eating similar diets and following similar workout regimens as individuals in the experimental group. Instead of the supplement, the control subjects would consume a placebo, a fake product that is identical in appearance to the dietary supplement.
When an experiment has been completed, the results must be interpreted. Accurate interpretation is just as important as conducting a study carefully. If a study conducted on a large group of men indicates that a change in diet reduces cancer risk, the results of that study cannot be used to claim the same effect in women. Likewise, if the study looks only at the connection between a change in diet and colon cancer, the findings can’t be used to claim a reduced risk for other cancers.

One way to ensure that the results of experiments are interpreted correctly is to have them reviewed by experts in the field who did not take part in the study being evaluated. This peer-review process is used in determining whether experimental results should be published in scientific journals. The reviewing scientists must agree that the experiments were conducted properly and that the results were interpreted fairly. Nutrition articles that have undergone peer review can be found in journals such as "The American Journal of Clinical Nutrition", "The Journal of Nutrition", "The Journal of the American Dietetic Association", "The New England Journal of Medicine", and "The International Journal of Sport Nutrition". Newsletters from reputable institutions, such as the "Tufts Health and Nutrition Letter" and the "Harvard Health Letter", are also reliable sources of nutrition and health information. The information in these newsletters comes from peer-reviewed articles but is written for a consumer audience.

By Mary B. Grosvenor and Lori A. Smolin (University of Connecticut) in the book "VISUALIZING NUTRITION" - EVERYDAY CHOICES, published by John Wiley & Sons U.S.A in collaboration with The National Geographic Society, excerts from pages 12 to 18. Copilated, adapted to be posted by Leopoldo Costa. Pictures from the book.