Human Nutrition - Genetics, evolution, and obesity + scientific method + BMI

Scientific Inquiry

Nutrition is based on scientific study (data)

• integrates biology, physiology, microbiology, botany, chemistry, genetics and molecular biology

The Scientific method

• Is hypothesis driven

1. Ask a question (define the problem)

2. From a hypothesis

3. Design an experiment

4. Collect, analyze and interpret the data

5. Generalize and publish findings

6. Ask another question (the findings generally lead to more questions)

Research Designs

• Case

• Clinical

• Epidemiology and intervention

• Laboratory

Case study

studies results from one person

Clinical Study

Experimental design with a group of people

Epidemiology and intervention Study

population based, retrospective or prospecive

Laboratory Study

experimental design with a life form

Experimental designs

• Number of subjects: statistical significance

• Duration of the study: long enough to draw conclusions

• Matching groups: ethnicity, gender, age, lifestyle, and disease

• Control groups: experimental vs placebo

• Reproducible results: repeat experiment yields same results

• The treatment protocol: blind, double

Diseases at risk due to obesity

• Hyperglycemia and type 2 diabetes

• High BP, heart disease and stroke

• Cancer (13 different types)

• Liver/gallbladder disease

• Arthritis

• High-risk pregnancy

Principles of energy balance

• 1 pound fat = 3500 calories stored

• To lose body fat, a calorie deficit needs to be created

• Changes in body weight based on caloric intake and energy expenditure

Basal Metabolic Rate

An amount of energy needed to sustain life

• Determined in a fasting state and when body is at complete rest

• Cannot control, majority of expenditure

• Increased muscle mass increases BMR - muscle cells need more energy

Things that effect BMR

• Age: BMR is reduced with age

• Gender: more lean mass = higher BMR

• Physiological state: illness, pregnancy, lactation, stress, metabolic diseases (hyperthyroidism) can increase BMR

• Physiological state: starvation or prolonged fasting decreases BMR

• Environmental temperature: extreme hot or cold temps temporarily increase BMR

Physical activity (PA)

• Energy expended to perform physical activity

• Voluntary muscle movement

• total amount of E expended increases with body weight and exercise intensity

Specific Dynamic Action (SDA) - aka thermic effect of food

• ‘Cost” of digesting, absorbing, and assimilating nutrients

• 5-10% of the total calories consumed used in the digestion, absorption, and assimilation (DAA) of nutrients

• Highly processed food need less calories to DAA

• BMR increases when fed

Healthy Body Composition

• Lean body mass = ~55% of total body weight 

  • muscle = ~70% H20

• Essential fat mass 

  • 3% body fat in men

  • 12% body fat in women

• Stored fat mass is variable ~15-20%

  • additional fat beyond essential fat is stored

• Minerals = ~4% of total body weight

• Water = ~60% of total body weight 

How do bodies regulate blood sugar (homeostasis)

• Consume macronutrients (calories)

• Body metabolizes into glucose → blood sugar goes up

• Insulin is released form the pancreas

• Pulls blood sugar out of blood forming glycogen

• Glycogen deposits

• Eat until glycogen is replenished

• Fast → blood sugar drops

• Glucagon

Insulin

a hormone produced by the pancreas, plays a crucial role in human nutrition by regulating blood sugar levels, facilitating glucose uptake into cells for energy, and promoting the storage of excess glucose as glycogen or fat. 

Glucagon

Counteracts insulin effects, primarily by increasing blood glucose levels during fasting or when blood sugar drops ensuring the body has sufficient energy

Shades of a cell

• Brown fat cell

  • converts chemical energy to heat to protect against cold weather

• Beige fat cell

  • immature cell in white fat tissue matures to burn fat

• White fat cell

  • most common fat cell, used to store fat and found beneath the skin and abdomen

Glycogen

the stored form of glucose, doesn’t directly turn into fat, but its levels and turnover influence how the body stores and uses energy potentially impacting fat storage

Excess Fat

Excess dietary fat, especially when calories intake exceeds energy expenditure, leads to fat storage in the body, primarily triglycerides in tissue, contributing to weight gain and potential health issues