Scientific Inquiry
Tied to Genetics,
Evolution, and
Obesity
By Jennifer Turley and Joan Thompson
© 2016 Cengage
Presentation Overview
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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.
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,
Part 1
• 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)
The Scientific Method, Part 2
Design the study to
test the hypothesis
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
Cell
Evolution
Set Point
Thrifty gene
Glucostatic
Scientific Explanation
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.
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.
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.
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.
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.
Research Designs
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Case studies
Clinical studies
Intervention trials
Epidemiology
Laboratory experiments
Testimonials are NOT based on
research
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 Design
Things 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.
Public Recommends
• 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).
Epidemiological study
results reveal an obesity
epidemic
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
BMI
19
20
21
22
23
24
25
26
Ht
27
BMI
RISK
<18.5
18.5-24.9
25-29.9
30-34.9
35-39.9
≥40
Underweight
Normal
Overweight
Obesity (class I)
Obesity (class II)
Extreme Obesity
28
29
30
31
32
33
34
35
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
Obesity Trends* Among U.S. Adults
BRFSS, 1990 and 2012
(*BMI 30, or about 30 lbs overweight for 5’4” person)
For updates go to
http://www.cdc.gov/nccdphp/dnpa/obesity/trend/maps/
Why is Obesity of
Concern? Part 1
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? Part 2
Increased risk for chronic diseases
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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? Part 3
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
Some Summary Points
• 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