weeks 1-3

Organisation of the Gastrointestinal System

• The gastrointestinal tract is a tube that is specialised along its length for sequential processing of food.
• It consists of a series of hollow organs (from mouth to anus) and accessory glands and organs that add secretions to the hollow organs.
• Each hollow organ serves a specialised function, separated at key locations by sphincters.

Functions of Gastrointestinal Organs

• Mouth and Oropharynx: mechanical breakdown and lubrication of food, propulsion of food into the oesophagus, and initiation of fat and carbohydrate metabolism.
• Oesophagus: conduit to the stomach.
• Stomach: temporary food storage, churning, and secretion of proteases and acid to facilitate digestion.
• Small intestine: continues digestion, primary site for nutrient absorption.
• Large intestine: reabsorbs fluids and electrolytes (but no nutrient absorption), storage of faecal matter before expulsion.
• Accessory glands include salivary glands, pancreas, and liver.

Pancreas and Liver

• Pancreas: secretes digestive enzymes, bicarbonate to neutralise gastric acid, and secretes into the duodenum via the major and minor duodenal papilla.
• Liver: secretes bile (stored in the gallbladder between meals), bile acids within bile play a key role in fat digestion.

Nutrient Digestion and Absorption

• Digestion: enzymatic conversion of complex dietary substances to a form that can be absorbed.
• Absorption: process of taking up nutrients into cells or across tissues and organs through diffusion or osmosis.

Carbohydrate Digestion

• Carbohydrates are classified into three major groups: monosaccharides, disaccharides, and polysaccharides.
• The small intestine can directly absorb monosaccharides, but not polymers.
• Dietary fibre is a non-digestible polymer found in fruits, vegetables, and cereals.
• Glycogen is the storage form of carbohydrate in animals.

Carbohydrate Digestion Steps

• Intraluminal hydrolysis: starch to oligosaccharides by salivary and pancreatic enzymes.
• Membrane digestion: oligosaccharides to monosaccharides by brush border disaccharidases.

Intraluminal Hydrolysis

• Salivary and pancreatic acinar cells synthesise and secrete alpha-amylases.
• Salivary amylase initiates starch digestion in the mouth, but is inactivated by gastric acid.
• Pancreatic alpha-amylase completes starch digestion in the small intestine.

Membrane Digestion

• Membrane digestion involves hydrolysis of oligosaccharides to monosaccharides by brush border disaccharidases.
• The small intestine has three brush border oligosaccharidases: lactase, maltase, and sucrase-isomaltase.

Carbohydrate Absorption

• The three monosaccharide products of carbohydrate digestion are absorbed by the small intestine in a two-step process.
• Uptake across the apical membrane into the epithelial cell, and coordinated exit across the basolateral membrane.

Protein Digestion

• Proteins must be digested into their constituent oligopeptides and amino acids before being taken up by the enterocytes.
• Digestion-absorption of proteins occurs through four major pathways.

Protein Digestion Pathways

• Luminal enzymes hydrolyse proteins to peptides and amino acids, which are then absorbed.
• Luminal enzymes digest proteins to peptides, which are then digested to amino acids by brush border peptidases.
• Luminal enzymes digest proteins to peptides, which are taken up by enterocytes and further digested to amino acids by cytosolic enzymes.
• Luminal enzymes digest proteins to oligopeptides, which are taken up by enterocytes and moved directly into the blood.

Protein, Peptide, and Amino Acid Absorption

• In adults, proteins are almost exclusively digested to their constituent amino acids and dipeptides, tripeptides, or tetrapeptides before absorption.
• The absorption of amino acids across the small intestine requires sequential movement across both the apical and basolateral membranes of the villous epithelial cell.

Lipid Digestion

• Lipids are typified by their preferential solubility in organic solvents, compared with water.
• The biological fate of lipids depends critically on their chemical structure and interactions with water and other lipids in aqueous body fluids.

OVERWEIGHT & OBESITY

• Overweight and obesity are associated with, if not the principal cause of, much disease and disability
• Short-term interventions have limited effectiveness, and long-term success is rare without ongoing medical efforts
• Obesity is a chronic illness, often with comorbidities that need to be considered
• Significant weight loss has far-ranging positive health effects and can often control or eliminate comorbidities
• Exercise and dietary changes are the main contributors to weight loss

GLOBAL OBESITY EPIDEMIC

• According to WHO, obesity (BMI > 30) has tripled worldwide since 1975
• In 2016, at least 2.5 billion people were either overweight or obese, with 600 million categorized as obese
• Overweight and obesity cause more deaths than being underweight
• Obesity has led to discrimination in recent years, with many viewing it as a moral or social issue, stigmatizing its management

HEALTH RISKS OF OBESITY

• Obesity is associated with an increased rate of death from all causes, particularly cardiovascular disease
• Obesity and sedentary lifestyle are considered the second leading cause of preventable death in the USA, and may overtake tobacco abuse within the next decade
• For obese individuals, life expectancy decreases by about 7 years compared to normal-weight individuals

OVERWEIGHT & OBESITY IN AUSTRALIA

• In Australia, per capita spending is approximately $830 more for an obese individual versus someone of normal body weight
• Obesity reduces life expectancy, and this effect is more powerful in those who develop obesity earlier in life
• In 2016, life expectancy fell slightly for the first time, reflecting the effects of obesity-related chronic illness on society

MANAGEMENT OF OBESITY

• Exercise, diet modifications, and lifestyle changes are the foundation of a behavioral-based approach to the management of obesity
• A long-term-horizon approach is imperative to success
• Using a behavior change approach is critical

ASSESSMENT OF BODY COMPOSITION

• Body Mass Index (BMI) indicates overweight for height, but does not discriminate between fat mass and lean tissue
• BMI has significant correlation with total body fat and is an acceptable clinical measure of overweight and obesity
• BMI thresholds vary internationally by race
• Other methods for assessing body composition include skinfolds, bioelectrical impedance, water or air displacement, and dual-energy x-ray absorptiometry (DEXA)

CHILDHOOD OBESITY

• 70% of all obesity begins in adulthood
• There is a strong association between childhood obesity and the risk of adulthood obesity, affected by the severity of childhood obesity, age of onset, and whether the parents are also obese
• Most obese children will carry their obesity into adulthood
• Increasing childhood obesity is a worldwide issue

CENTRAL ADIPOSITY

• BMI > 30 carries increased health risk for obesity-related comorbidities, including heart disease, diabetes, hypertension, dyslipidaemia, sleep apnoea, and gastro-oesophageal reflux disease (GORD)
• The pattern of fat distribution also affects risk

PATHOPHYSIOLOGY OF OBESITY

• Ghrelin, produced as the stomach empties, triggers the central nervous system appetite stimulant neuropeptide Y (NPY), growth hormone, and norepinephrine
• Weight loss can increase serum ghrelin levels, which may explain part of the process that makes sustaining weight loss difficult
• Cholecystokinin, serotonin, and peptide YY are among a group of central nervous system and gut peptides involved in satiety and reduced food intake

Exercise Testing

• Exercise testing is used to assess for coronary artery disease in overweight or obese individuals.
• The test is also used to determine functional capacity and develop an exercise prescription based on heart rate.
• Walking is the preferred mode of exercise, but it may not be practical for obese individuals.
• Seated devices such as upper body ergometers, stationary cycles, or recumbent stepping machines can be used as alternatives.
• A low-level protocol with small increments (e.g., 0.5-1.0 MET) may be preferred due to the potential for low peak exercise capacity.

Treatment

• Treatment goals should consider both medical benefits and patient expectations.
• International guidelines recommend a 10% weight loss within 4-6 months and weight loss maintenance as an initial goal.
• This amount of weight loss is associated with several health-related benefits.
• Patients often want to lose 35% of their weight to attain their desired weight.

Diet Therapy

• To lower weight, energy balance must be negative, and calorie reduction is the essential first step.
• For normal adults, 22 kcal/kg is required daily to maintain weight.
• A bell-shaped curve describes a variation in average energy expenditure of about 20%.
• The lowest calorie level for weight maintenance is about 1,200 kcal daily, even for those at bed rest.
• Exercise and activity levels affect maintenance calorie levels by 25% or more.

Diet Therapy - Rapid Weight Loss

• A deficit of 7,700 kcal is needed to lose 1kg, so a typical diet can yield about 0.5kg of weight loss per week.
• Low-fat diets are recommended due to the high calorie content of fat and the heart health benefits.
• Higher-protein and lower-carbohydrate diets have been favored by patients due to greater weight losses and better satiety.
• Higher-protein diets tend to promote satiety, and lower-carbohydrate levels can promote greater fat utilization.

Medical Management

• Medically supervised very low-calorie diets can be used for rapid weight loss.
• Ozempic (Semaglutide) and Saxenda (Liraglutide) are injectable diabetes medications that can be used at higher doses for weight loss.
• These medications can achieve modest weight loss in completers (~4-5% of baseline weight) in trials of up to one year.

Surgical Therapy

• Surgical procedures can restrict the stomach or cause malabsorption of food, or both.
• Newer laparoscopic techniques can cause patients to lose one-third of their weight (>50% of their excess weight) within 18 months.
• Research has confirmed improved mortality rates with weight loss surgery, but there are significant risks (up to 1% for death and 15% for morbidity).
• Surgery is typically restricted to those with a BMI ≥ 40 or those with a BMI ≥ 35 if they have obesity-related comorbid conditions.

Exercise Prescription

• Exercise alone can achieve weight loss, but high amounts of total caloric expenditure are required (>3,000 kcal/week).
• Exercise and caloric reduction can increase the weekly rate of weight loss by approximately 1kg over caloric reduction alone.
• Regular exercise of 60-90 minutes on most days of the week is recommended for long-term weight loss maintenance.

Cardiorespiratory Exercise

• Initially, exercise and physical activity should focus on cardiorespiratory exercise.
• Typical RPE values of 11-15 (6-20 scale) may be substituted when assessing heart rate is not convenient.
• Interval training is not part of an initial exercise routine, but some individuals who establish and tolerate a regular exercise routine may enjoy this form of training.

Exercise Duration

• For those with little or no previous recent exercise history, beginning with 20-30 minutes each day is appropriate.
• Breaking this exercise time into two or three sessions per day of shorter duration (5-15 minutes) may be required for extremely deconditioned people.
• The focus should be on duration before intensity.
• Accumulation of time over several sessions in a day is as beneficial as one continuous work bout with respect to total caloric expenditure.

Resistance Exercise

• The exercise prescription for obese people should include resistance intensity in the range of 60-80% of 1RM, performed for 8-12 reps and two sets (progressing to as many as four sets).
• This plan will allow the person to perform 6-10 exercises in a 30-40 minute session.
• Resistance exercises can be performed maximally on 2-3 days/week, ideally without working the same muscle groups on consecutive days.

Range of Motion

• Obese patients have a reduced range of motion primarily due to increased fat mass surrounding joints and a lack of movement and routine stretching.
• ROM may improve spontaneously with weight loss.
• Normal flexibility routines are recommended as tolerated.

Exercise Training - Important Considerations

• Low cardiorespiratory fitness adds to the risk of cardiovascular disease and mortality in overweight and obese people.
• Ample evidence indicates that regular aerobic exercise training improves physical functioning, independent of weight loss, in those who are obese or overweight.
• Exercise training is likely most important in the weight maintenance process of weight control.
• Regular exercise training expending more than 2,000 kcal/week is a strong predictor of long-term weight loss maintenance.

Hyperlipidemia and Dyslipidemia

• Lipids are necessary for normal body functioning, including cholesterol, triglycerides, and lipoproteins.
• Abnormal lipid levels, particularly of cholesterol, triglycerides, and lipoproteins, are modifiable CVD risk factors.
• Dyslipidemic patients have an elevated risk of CVD.

Cardiovascular Testing

• The purpose of cardiovascular testing in individuals with dyslipidemia is to help diagnose CAD, determine functional capacity, and determine an appropriate exercise intensity range.
• Prescribed medications can alter anticipated exercise responses, such as lipid-lowering medications like statins and fibric acid, which can cause muscle damage and reduce exercise performance.

Musculoskeletal Testing

• 1RM tests can be used, and patients who are responsible drinkers should be encouraged to continue moderate alcohol use.

Diet

• Diets with fat intake exceeding 35% are likely to include too much saturated fat, contributing to elevated LDLc, insulin resistance, and weight gain.
• Low-fat, high-carbohydrate diets promote features of atherogenic dyslipidemia, such as elevated triglycerides and lower HDLc.
• Functional foods, including soluble fiber, plant stanols and sterols, psyllium, flaxseed, nuts, omega-3 fatty acids, garlic, flavonoids, and soy protein, may be effective for blood lipid management.

Effects of Grapefruit

• Grapefruit chemicals do not interact directly with statin medications, but rather bind to an intestinal enzyme, blocking its action and making the passage of the medication easier from the gut to the bloodstream.
• As a result, blood medication levels may rise faster and remain at higher-than-normal levels, which can be dangerous in some cases.

Cardiorespiratory Exercise

• People should accumulate 150-300 minutes of moderate-intensity or 75-150 minutes of vigorous-intensity dynamic physical activity using large muscle groups, or some combination of the two, throughout each week.
• To optimize lipid and lipoprotein changes, clients are encouraged to progress to the upper end of the exercise dose range.
• Leisure-time physical activity should be practiced on at least 3 days through the week, and 5 or more days are required for most people to meet the dose recommendations.

Resistance Exercise

• Resistance training alone may have very limited effect on improving blood lipid and lipoprotein concentrations.
• Since cardiorespiratory exercise should be prioritized, more than one set per resistance training exercise is not recommended unless the client is clearly motivated to be compliant with both cardiorespiratory and resistance exercise.

Range of Motion Exercise

• ROM exercise provides no known benefit to lipid or lipoprotein profiles.
• Unless certain comorbidities exist, there are no special considerations for dyslipidemic patients with respect to ROM exercise.

Exercise Considerations

• Patients should be instructed to inform their AEP whenever their medications are changed, or the dosages are increased.
• In such cases, increases in exercise volume should be withheld for a couple of weeks, and any unusual muscle soreness should be noted.
• Any sudden or severe muscle pain that cannot be logically explained by a recent increase in physical activity should be brought to the attention of the patient’s GP.

Exercise Prescription Summary

• There is strong evidence for lower triglyceride and greater HDLc concentrations in physically active individuals.
• Triglyceride levels are almost always lower in endurance athletes, aerobically trained people, and physically active individuals when compared with sedentary controls.
• Blood levels of HDLc are between 9% and 59% higher in those having physically demanding jobs and in individuals engaged in endurance exercise compared with their less active counterparts.
• There is only limited evidence to suggest that people who are physically active exhibit lower concentrations of total cholesterol and LDLc than those who are less active.