Scientific InquiryTied to Genetics,

Evolution, and Obesity

By Jennifer Turley and Joan ThompsonBy Jennifer Turley and Joan Thompson

© 2013 Cengage© 2013 Cengage

• The field of nutritional sciences• The process of science• The scientific method• Research/study designs• How dietary recommendations

are made• Epidemiological study results

reveal an obesity epidemic.

Presentation Overview

Scientific Inquiry

• The field of nutrition is based on scientific study that integrates biology, physiology, microbiology, botany, chemistry, genetics and molecular biology.

• In order to understand how evidence is produced, it is crucial to understand the basics of scientific inquiry.

The Scientific Method• Is hypothesis driven• Follows a basic format

– Ask a question (define the problem)– Form a hypothesis– Design an experiment– Collect, analyze & interpret the data

– Generalize & publish the findings– Ask another question (the findings

generally leads to more questions)

Design the study

to test the hypothesis

The Scientific Method

A validated hypothesis may lead to a theory such as the theory of evolution or the thrifty gene theory

Examples of Theories in Science and Nutrition

Theory Scientific ExplanationCell The cell is the most basic unit of life, organisms are made of one or more cells, and new

cells arise from existing cells. Years ago it was hypothesized that humans are born with a certain number of fat cells. Now it is known that fat cells can divide when they have been filled to capacity.

Evolution The change in heritable genetic composition of a population, such as by gene mutation and as a result of natural selection. There are several theories about how life forms began on earth; the well accepted theory of evolution is one of them.

Set Point There seems to be a range of body weight that is relatively easy to maintain and is genetically and physiologically controlled. The lower body weight range is more tightly defended to prevent starvation and preserve life. There are many feedback mechanisms that influence intake and satiety.

Thrifty gene Humans who efficiently stored food energy as body fat survived tough times during the hunter-gatherer period of human existence. Natural selection of these thrifty genetic traits through evolution may lead to present day obesity when the person lives in a toxic food environment and leads a sedentary lifestyle. There are many factors involved in survival; energy storage ability is one of them.

Glucostatic Blood glucose levels affect overall bodyweight; mild hypoglycemia is associated with elevated levels of insulin which inhibits the satiety center and promotes positive energy balance. Normal glycemia results in satiety and better weight control. There are many factors involved in bodyweight control; glycemia is one of them.

• Case studies• Clinical studies• Intervention trials• Epidemiology • Laboratory experiments

Research Designs

Study Types• Case: Results from a single person

protocol conducted by a medical doctor.• Clinical: Experimental design with a

group of people.• Epidemiological & Intervention:

Population based, retrospective or prospective.

• Laboratory: Experimental design with any life form; microorganisms, virus, animals, plants, cell lines, bugs, etc.

Experimental Designthings to consider

1. Number of Subjects: is there enough for statistical significance.

2. Duration of the Study: is it long enough for conclusions to be made.

3. Matching Groups: Ethnicity, gender, age, lifestyle, disease.

4. Control Groups: experimental vs placebo.

5. Reproducible Results: can the experiment be repeated and yield the same results.

6. The Treatment Protocol: blind, double blind, crossover.

Treatment Protocol• Blind: the subject does not know if they

are in the experimental or control group.• Double Blind: the subject and the

primary investigator do not know who is in the experimental or control group.

• Cross over: each group experiences a period of being on the placebo and experimental drug.

• A highly reputable study design is called the double-blind cross over experiment.

• Consistent results from multiple credible studies published over many years are used to make dietary recommendations.

• A whole body of evidence, collected over many years of experimentation is interpreted by the scientific community to create public recommendations regarding diet and health (disease prevention).

Public Recommends

Epidemiological study Epidemiological study results reveal an obesity results reveal an obesity

epidemicepidemic

Obesity: An Epidemic• Obesity is body fatness

significantly in excess of the level that is consistent with optimal health.

• There has been an uncontrolled rise in obesity in the United States over the last 20 years.

• Obesity is defined by Body Mass Index (BMI).

BMI RISK<18.518.5-24.925-29.930-34.935-39.9≥40

UnderweightNormalOverweightObesity (class I)Obesity (class II)Extreme Obesity

BMIBMI= wt(kg)÷[ht(m)]2

BMI 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Ht Wt (lbs)

60 97 102 107 112 118 123 128 133 138 143 148 153 158 163 168 174 179

61 100 106 111 116 122 127 132 137 143 148 153 158 164 169 174 180 185

62 104 109 115 120 126 131 136 142 147 153 158 164 169 175 180 186 191

63 107 113 118 124 130 135 141 146 152 158 163 169 175 180 186 191 197

64 110 116 122 128 134 140 145 151 157 163 169 174 180 186 192 197 204

65 114 120 126 132 138 144 150 156 162 168 174 180 186 192 198 204 210

66 118 124 130 136 142 148 155 161 167 173 179 186 192 198 204 210 216

67 121 127 134 140 146 153 159 166 172 178 185 191 198 204 211 217 223

68 125 131 138 144 151 158 164 171 177 184 190 197 203 210 216 223 230

69 128 135 142 149 155 162 169 176 182 189 196 203 209 216 223 230 236

70 132 139 146 153 160 167 174 181 188 195 202 209 216 222 229 236 243

71 136 143 150 157 165 172 179 186 193 200 208 215 222 229 236 243 250

72 140 147 154 162 169 177 184 191 199 206 213 221 228 235 242 250 258

73 144 151 159 166 174 182 189 197 204 212 219 227 235 242 250 257 265

74 148 155 163 171 179 186 194 202 210 218 225 233 241 249 256 264 272

75 152 160 168 176 184 192 200 208 216 224 232 240 248 256 264 272 279

1991

(*BMI 30, or about 30 lbs overweight for 5’4” person)

Obesity Trends* Among U.S. AdultsBRFSS, 1991, 1999, 2008, and 2010

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2008

No Data <10% 10%–14% 15%–19% 20%–24% 25%–29% ≥30%

2010

Why is Obesity of Concern?

Increased risk for chronic diseases

Type 2 diabetes • Type 2 diabetes is becoming

more prevalent in obese adults & children.

• Obese children are more likely to become obese adults.

• The onset of Type 2 diabetes is preventable by diet, exercise & a good weight control program.

Why is Obesity of Concern?

Increased risk for chronic diseases

• Type 2 diabetes • Heart disease & Cancer• Liver/gallbladder disease• Arthritis• High-risk pregnancy• Hernia & Varicose veins• Accidents• Depression & Low self esteem

Why is Obesity of Concern?

Increased risk for medical conditions

• High blood pressure (hypertension)

• High blood cholesterol and triglycerides

• High blood sugar • Overall obesity leads to

decreased longevity and decreased quality of life

Summary• Nutrition has relied upon scientific study to understand

the relationships between diet and disease. • Data synthesis from multiple study types (laboratory,

case study, & epidemiology).• Data synthesis across numerous disciplines

(physiology, anatomy, chemistry, immunology, virology, etc) over time.

• With consistent results have helped answer questions pertaining to human health.

• Epidemiological study results have verified the obesity epidemic.

• Obesity increases the risk for many chronic diseases and medical conditions.

References for this presentation are the same as those for this topic found in module 4 of the textbook