The recent discovery of the skeleton of a three-foot tall adult female belonging to a new human-like species, Homo floresiensis, is exciting news to anthropologists. The new species, named after the island on which the skeleton was discovered, appears to be descended from populations of Homo erectus, the closest known relative of modern humans. The skeleton was estimated to be 18,000 years old. This means that populations of Homo floresiensis existed well after modern man appeared approximately 160,000 years ago. Thus, researchers are wondering if the two species interacted. 

The first descendents of Homo floresiensis to reach Flores Island may have been similar in size to Homo erectus. Researchers hypothesize that the small size of Homo floresiensis (only three feet tall) is due to a process known as "island dwarfing." This phenomenon  has been observed in other mammals, where local isolation, absence of predators, and small population sizes, combined with restricted resources, lead to reductions in body size and modifications in brain size. The smaller individuals with reduced energy requirements are favored by natural selection in environments where food is limited and there is no need for defense against predators. In a small population with a limited gene pool, these changes could occur quite rapidly.

This presentation provides background science and health information related to the “Food and Fitness” unit created by scientists and educators at Baylor College of Medicine’s Center for Educational Outreach. The unit covers concepts related to energy, Calories, metabolism, diet and nutrition, and is particularly appropriate for students in grades 5–8. Viewing this presentation also fulfills part of the requirements for the Virtual Workshop on Energy, Food and Nutrition (“Food and Fitness”) offered for professional development contact hours on BioEd Online.

Funding for development of the Food and Fitness unit and accompanying online professional development was provided by the National Space Biomedical Research Institute (NSBRI), a consortium of leading biomedical research centers funded by the National Aeronautics and Space Administration (NASA). Visit the following sites for more information about these organizations:

Center for Educational Outreach, Baylor College of Medicine  http://www.ccitonline.org/ceo
National Space Biomedical Research Institute  http://www.nsbri.org
National Aeronautics and Space Administration http://www.nasa.gov

PowerPoint slides were written by Nancy Moreno to compliment Roberta Andings’ presentation on Adolescent Nutrition to a Food and Fitness Teacher Education Workshop in March, 2004.

The incidence of obesity among six- to eleven-year-olds in the US has more than doubled in the past 20 years (USDHHS, 2004). As reported by the Office of the Surgeon General (USDHHS, 2001), most young people are not following  recommendations set forth in the Dietary Guidelines for Americans. For example, 67%  of youths aged 6-19 exceed dietary guidelines for fat intake and 72%  exceed recommendations for saturated fat intake.

Most nutritional problems in adolescents are related to the consumption of too much “junk food,” or food with limited or no nutritional value. Most junk food is characterized by high levels of fats, particularly saturated fats, and refined sugar. The portion sizes of junk food also typically are very large. In addition, most adolescents eat very few fruits and vegetables per day or chose items, such as iceberg lettuce, with low nutritional values.

The eating habits of today’s adolescents will lead to future health care problems. Obesity is related to a number of health problems, including Type 2 Diabetes, heart disease, stroke and cancer (NHLBI, 2004). Osteoporosis also is a growing problem, even among adolescents. Poor nutrition and insufficient exercise both contribute to low bone density among teenagers.

Junk food is food with minimal nutritional value. Most junk food is characterized by high fat and sugar content, with few other nutrients. Examples of junk foods include sweetened soft drinks, fried foods, particularly French fries, chips and other snacks, and candy. Without guidance, most adolescents will not make healthy food choices.

Portion sizes of junk food have increased dramatically over the past 20 years. For example, when most fast food franchises originated, a “regular” serving of French fried potatoes contained 201 Calories. Today, a “supersized” serving of fries contains approximately 610 Calories (NHLBI, 2004). The packaging of many kinds of junk foods in bags or pouches makes it difficult for consumers to estimate and compare serving sizes.

Sugar-sweetened beverages are now the principal source of added sugars in the diets of Americans (Guthrie, 2000). High sugar drinks, including fruit juices, contribute large of amounts of calories to the diets of adolescents. Further, most people do not reduce their consumption of other foods to compensate for the high number of calories consumed as sweetened beverages.

Many Americans overestimate portion sizes. When teaching portion sizes, it can be helpful to have students estimate the number of servings of juice or other drinks contained in a typical drinking glass. Even though a serving of fruit juice typically is four ounces, most adolescents drink from glasses that contain between 10 and 16 ounces of liquid. Soft drinks are a major source of hidden added Calories in adolescents’ diets.

Restaurants often serve quantities of food that exceed a single portion size. For example, a typical “super-sized” meal can contain as many as 1,500 to 2,000 Calories—almost an entire day’s worth of Calories—in a single meal or snack. A sedentary lifestyle also contributes to obesity. In particular, television viewing has been linked to weight gains and obesity among young people. Researchers have hypothesized that television viewing contributes to obesity by displacing physical activity, increasing calorie consumption while watching (including the effects of advertising) and reducing resting metabolism (Robinson, 2001).

Food labels and other guides often use “serving size” to describe a recommended single portion of a food. Serving sizes are different for various kinds of food (liquid vs. solid, or cooked vs. raw). In general, adolescents tend to overestimate portion sizes. The “Nutrition Facts” labels on most foods provide important information about serving sizes and the number of servings contained within a single package. For example, even though most soft drink consumers drink an entire 12- or 16-ounce container at one time, most soft drink labels identify the contents as two or more servings.

Students need easy guidelines to help them estimate appropriate serving sizes of different kinds of foods. Some rules of thumb include the following.

Palm of hand or deck of cards = one serving of meat, fish or poultry.
Size of closed fist or a tennis ball = one serving (one cup) of rice, pasta, fruit or raw vegetables.
Cupped hand = one serving (one cup) of dry cereal.
Two fingers or a domino = one serving (one ounce) of cheese.
Tip of thumb = one serving (teaspoon) of butter or margarine.

Consumption of large food portions, combined with sedentary lifestyles, is linked to overweight and obesity in adolescents and adults.

Serving sizes on food labels are designed to make it easier to compare the calorie and nutritional content of similar products and to identify nutrients present in a food. At a minimum, food labels contain information about serving sizes; calories; calories from fat (dietitians generally recommend that no more than 30% of calories come from fat over the course of the day); percent daily values of major nutrients; total fat; saturated and trans fat (these unhealthy fats are listed under total fat—saturated fat and trans fat raise cholesterol and increase a person's risk for developing heart disease); unsaturated fats (liquid at room temperature, these are the healthy fats); cholesterol; sodium; total carbohydrates (which includes dietary fibers, sugars, and other carbohydrates); protein; vitamins A and C; calcium and iron.

Carbohydrates are the most abundant source of calories in most people’s diets. Carbohydrates are either simple (called sugars) or complex (called starches). Cereals, rice, potatoes, breads, pastas, fruits, and vegetables all contain high amounts of carbohydrates. Not all sugar in food is added. Lactose, or milk sugar, is a natural ingredient in milk. Fruit also has high amounts of naturally occurring sugar.

When reading a food label, it is important to pay attention to the number of servings contained within a package and the amount of saturated fat. Saturated fat contributes to heart disease—the number one killer of adults in the US. Most saturated fats are solid at room temperature. The words, "hydrogenated," "partially hydrogenated," or "shortening,” also are used to describe saturated fats.  With true “low-fat” foods, fewer than 30%  of the total calories come from fat.

Students are not always able to make optimal food choices. Thus, it is important to help them select healthier alternatives when confronted with several imperfect options in the school cafeteria or at a fast food restaurant. In other words, students can learn to make better “bad choices.” In general, it is advisable to drink water instead of sweetened soft drinks, reduce portion sizes, and avoid fried foods.

A dinner plate can be used to help students estimate appropriate amounts of foods. Approximately one half of the plate should contain fruits and vegetables. The other half should contain a protein source (fish, meat, poulty, beans) and a starch (potatoes, rice, bread).

Food lessons help students learn to sample and enjoy new foods. Try introducing a new fruit or vegetable in class each week. Students are more likely to try something new when it is introduced to the entire group.

Darwin spent many years collecting evidence from different sources to support his theory that evolution occurs through the process of natural selection. He carefully studied specimens that he and others had gathered from around the world, including several different species of finches from the Galapagos Islands. Darwin recognized, for example, that the different types of beaks he observed among the finches were related to different food sources and foraging patterns. Finches that fed on large seeds, for example, had thicker, stockier beaks, which contrasted with the more pointed beaks of finches that fed on cactus.

Darwin proposed that natural selection could explain how diversity-such as the diverse forms of beaks in the Galapagos finches-arises in nature. He reasoned that when environmental conditions change (e.g., alterations in temperature or sources of food), some individuals will have characteristics that allow them to continue to survive in the changed environment. These "successful" individuals will be more likely to produce more offspring than other less successful, and perhaps less well adapted individuals. Over time, the useful adaptive traits would become more common in the population, and the detrimental traits would become increasingly rare. In the example of the finches, birds with thick, stocky beaks would have a foraging advantage if the most abundant food source consisted of large, hard-shelled seeds. Individual finches whose beaks were most suited to seed eating would, theoretically, be able to consume more food. Therefore, birds with thick stocky beaks generally would be healthier and produce more offspring than individuals with less effective beaks. Over time, the population would come to be predominated by the stocky beak type.

It is important to recognize that evolution by natural selection, which many people think of as "survival of the fittest," is not strictly based on physical attributes, but rather, on differential reproductive success of individulas within a population. In a biological sense, "fitness" is equivalent to success in producing offspring that also survive and reproduce.

Darwin had little understanding of the underlying genetic mechanisms that drove natural selection. He knew, however, that for this system to work, the offspring must inherit the parent's physical characteristics. Thus, the basic elements of natural selection are that: (1) variation is present; (2) variation is heritable; (3) individuals within a population have different reproductive successes; and (4) individuals with higher reproductive success leave disproportionately more offspring.

This slide shows the protocol for the Wolfe bed rest study. Days 1-5 were the diet stabilization period in which initial measurements were made: lean leg mass (by DEXA* – Dual Energy X-Ray Absorptiometry); calf volume (by MRI); and a series of strength tests. On Day 6, the first tracer study** was done with a stable isotope to measure muscle protein synthesis. During days 7-33, subjects were in bed rest (with other samples collected and food intake controlled). Day 34 was a repeat of the tracer study done on Day 6, and Days 35-38 provided time for re-ambulation and repeats of measurements made on days 1-5. There were two groups, a placebo group and the group receiving the essential amino acid supplement.

* DEXA: a precise instrument that uses energy in the form of very small doses of X-rays to determine bone mineral density.
** Tracer studies: harmless radio isotopes are attached to specific amino acids that travel through the bloodstream. Blood samples are taken to determine the amount of amino acids that enter and leave the muscle.