chapter 09 physical activity and obesity. definitions: obesity: having a very high amount of body...

Chapter 09

Physical Activity and Obesity

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=znaqkfiacAntdM&tbnid=lCpsZ8yuyKv9SM:&ved=0CAUQjRw&url=http://www.viewzone.com/obesity.html&ei=4DpbUYHqA4f68QTY84C4Aw&bvm=bv.44697112,d.eWU&psig=AFQjCNFybudRMQBUWwDxUyR_gUt6EJ9D4Q&ust=1365019714216654


Definitions:• Obesity: Having a very high amount of body fat

in relation to lean body mass, or Body Mass Index (BMI) of 30 or higher.

• Body Mass Index (BMI): A measure of an adult’s weight in relation to his or her height, specifically the adult’s weight in kilograms divided by the square of his or her height in meters.

Source = CDC



Source of the data:• The data shown in these maps were collected through

CDC’s Behavioral Risk Factor Surveillance System (BRFSS). Each year, state health departments use standard procedures to collect data through a series of monthly telephone interviews with U.S. adults.

• Prevalence estimates generated for the maps may vary slightly from those generated for the states by BRFSS as slightly different analytic methods are used.

Source = CDC

Obesity Trends Among U.S. Adults between 1985 and 2010


• In 1990, among states participating in the Behavioral Risk Factor Surveillance System, 10 states had a prevalence of obesity less than 10% and no states had prevalence equal to or greater than 15%.

• By 1998, no state had prevalence less than 10%, seven states had a prevalence of obesity between 20-24%, and no state had prevalence equal to or greater than 25%.

• In 2006, only four states had a prevalence of obesity less than 20%. Twenty-two states had a prevalence equal or greater than 25%; Two of these states (Mississippi and West Virginia) had a prevalence of obesity equal to or greater than 30%.

• In 2009–2010, 35.7% of U.S. adults were obese.Source = CDC

Obesity Trends Among U.S. Adults between 1985 and 2006


1998

Obesity Trends* Among U.S. AdultsBRFSS, 1990, 1998, 2006, 2010

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

2006

1990

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


Obesity Trends* Among U.S. AdultsBRFSS, 1985

(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)

No Data <10% 10%–14%




No Data <10% 10%–14%




No Data <10% 10%–14% 15%–19%




No Data <10% 10%–14% 15%–19% ≥20%




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




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


Obesity Trends Among U.S. Adults


• BMI is used to Screen for Overweight in Children• For children and adolescents (aged 2–19 years), the

result is plotted on the CDC growth charts to determine the corresponding BMI-for-age percentile. Overweight is defined as a BMI at or above the 95th percentile for children of the same age and sex. This definition is based on the 2000 CDC Growth Charts for the United States. A child’s weight status is determined based on an age- and sex-specific percentile for BMI rather than by the BMI categories used for adults. Classifications of overweight for children and adolescents are age- and sex-specific because children’s body composition varies as they age and varies between boys and girls.

Source = CDC

Childhood Overweight


Trends in Childhood Overweight

Prevalence of Overweight* Among U.S. Children and Adolescents(Aged 2 –19 Years)

National Health and Nutrition Examination Surveys

Trend Summary (2012)



Consequences of Childhood Overweight

• Psychosocial Risks• Some consequences of childhood and adolescent

overweight are psychosocial. Overweight children and adolescents are targets of early and systematic social discrimination. The psychological stress of social stigmatization can cause low self-esteem which, in turn, can hinder academic and social functioning, and persist into adulthood

Source = CDC



• Cardiovascular Disease Risks• Overweight children and teens have been found to have

risk factors for cardiovascular disease (CVD), including high cholesterol levels, high blood pressure, and abnormal glucose tolerance. In a population-based sample of 5- to 17-year-olds, almost 60% of overweight children had at least one CVD risk factor while 25 percent of overweight children had two or more CVD risk factors.

Source = CDC



• Additional Health Risks• Less common health conditions associated with increased weight

include asthma, hepatic steatosis, sleep apnea and Type 2 diabetes.

• Asthma is a disease of the lungs in which the airways become blocked or narrowed causing breathing difficulty. Studies have identified an association between childhood overweight and asthma.

• Hepatic steatosis is the fatty degeneration of the liver caused by a high concentration of liver enzymes. Weight reduction causes liver enzymes to normalize.

Source = CDC



• Additional Health Risks• Sleep apnea is a less common complication of overweight for children and

adolescents. Sleep apnea is a sleep-associated breathing disorder defined as the cessation of breathing during sleep that lasts for at least 10 seconds. Sleep apnea is characterized by loud snoring and labored breathing. During sleep apnea, oxygen levels in the blood can fall dramatically. One study estimated that sleep apnea occurs in about 7% of overweight children.

• Type 2 diabetes is increasingly being reported among children and adolescents who are overweight. While diabetes and glucose intolerance, a precursor of diabetes, are common health effects of adult obesity, only in recent years has Type 2 diabetes begun to emerge as a health-related problem among children and adolescents. Onset of diabetes in children and adolescents can result in advanced complications such as CVD and kidney failure.

Source = CDC

How to break the cycle?

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=2HODKsLRusYiTM&tbnid=lPknLS8wuTkk3M:&ved=0CAUQjRw&url=http://www.schoolsforhealth.eu/index.cfm?act=nieuws.detail&nid=16&tid=1&ei=OElbUfHEJpOa9QT_lYHQCA&bvm=bv.44697112,d.eWU&psig=AFQjCNHVvKco5oWsa7HKQ6omtjnc_jqF_w&ust=1365023371328323

Treating Childhood Obesity

• Change family lifestyle. • Parents should be “agents of change” for

young children. • Use behavior modification to support long-

term change in behavior, including modifying the environment (e.g., removing cues to eat and adding cues to be active), monitoring behavior, setting and checking goals, and rewarding positive change.



• A review that compared lifestyle and drug treatments for obesity in children and adolescents found that 12 interventions, centered on increasing physical activity or reducing sedentary behaviors, had on average a significant effect on reducing BMI after six or 12 months. The effect was small compared to treatment with the drugs orlistat or sibutramine,(withdrawn from market) but the drugs had adverse side effects in the children

http://en.wikipedia.org/wiki/Orlistat

http://en.wikipedia.org/wiki/Sibutramine



• Increase physical activity: have children do more unstructured outdoor play; have them use active transport (e.g., walking or bicycling) to school and parks; provide transportation for sport participation when needed; parents should model an active lifestyle.

• Use nonconventional treatments, including weight loss drugs, as an adjuvant to support long-term lifestyle changes in adolescents who are obese.



• Change dietary intake and eating patterns: parents should model healthy food choices and have children eat lower-fat and lower-energy foods, increase fruits and vegetables, decrease portion sizes, and drink fewer sweetened beverages.

• Decrease time spent in sedentary behavior (e.g., limit television viewing and computer use to less than 2 h each day).



Consequences of Obesity In Adults

• Overweight and obese individuals are at increased risk for many diseases and health conditions, including the following:

• Hypertension (high blood pressure) • Osteoarthritis (a degeneration of cartilage and its underlying bone

within a joint) • Dyslipidemia (for example, high total cholesterol or high levels of

triglycerides) • Type 2 diabetes • Coronary heart disease • Stroke • Gallbladder disease • Sleep apnea and respiratory problems • Some cancers (endometrial, breast, and colon)

Source = CDC


Economic Burden of Obesity

• Article on the economic impact (burden) of obesity on The United States

Obesity cost the United States an estimated $147 billion in 2008, nearly 10% of all medical costs (Finkelstein et al. 2009). In a simulation model of population data, medical costs of obesity were higher than for smoking until people reached their mid 50s, after which smokers had higher costs. However, lifetime costs were still higher in people who were obese because smokers died at younger ages

http://www.brookings.edu/~/media/research/files/articles/2010/9/14%20obesity%20cost%20hammond%20levine/0914_obesity_cost_hammond_levine

Treatment of Obesity

• The NIH expert panel on obesity and overweight (National Heart, Lung, and Blood Institute 1998) reached these conclusions, though updates are expected in the near future:– Physical activity is a clinically accepted approach to weight loss,

as are low-calorie diets and lower-fat diets, behavior therapy, pharmacotherapy, surgery, and combinations of these techniques.

– For most overweight people, the initial goal of a prudent weight loss program is to lose about 10% of weight over a period of six months.

– After six months, the rate of weight loss usually declines, and weight tends to stabilize at a plateau because of the reduction in basal metabolic rate that results from the lower body mass

– Lost weight is usually regained unless a weight maintenance program consisting of dietary therapy, physical activity, and behavior therapy is continued indefinitely. After six months of successful weight loss, efforts to maintain weight loss should be undertaken.

Assessing and Defining Overweight and Obesity

• Quetelet’s body mass index (BMI) and relative weight are typically used to estimate overweight and obesity in epidemiologic studies because they are easy to assess in large numbers of subjects.


Patterning of Body Fat and Disease Risk

• Excess fat in the abdomen out of proportion to total body fat is another risk factor for chronic diseases associated with obesity.

• The waist-to-hip ratio predicts the patterning of visceral fat. Excess fat above the waist, so-called android fat, increases risk for CHD more than does excess fat below the waist, so-called gynoid fat. The American Heart Association (2001) suggests that the desirable waist-to-hip ratio is less than 1.00 for men and less than 0.80 for women.

• Table 9.3 (next slide) illustrates the additive risk of increased abdominal fat to the risk of BMI in the development of obesity-associated diseases in adults with a BMI of 25 to 34.9 kg/m2. Waist circumference does not add to the accuracy of predicting disease risk in people who have a BMI of 35 kg/m2 or more.


Patterning of Body Fat and Disease Risk

The Consensus About Obesity

• In 1995, the National Heart, Lung, and Blood Institute’s Obesity Education Initiative and the National Institute of Diabetes and Digestive and Kidney Diseases assembled an expert panel charged with the identification, evaluation, and treatment of overweight and obesity in adults. Their guidelines (based on 236 clinical studies), which appeared in 1998 are as follows:

• Treatment of overweight is recommended only when patients have two or more risk factors or a high waist circumference. Treatment should focus on altering dietary and physical activity patterns to prevent development of obesity and to produce moderate weight loss.


The Consensus About Obesity• Cardiovascular risk factors among obese people do not differ from

those for people of normal weight.• Obese people who have at least three major CHD risk factors

usually require medical treatment aimed at risk reduction. Their CHD risk is increased further if they are physically inactive and have high serum triglycerides (>200 mg/dl), though the increased risk has not been quantified.

• There is strong evidence that weight loss among people who are overweight or obese reduces risk factors for diabetes and cardiovascular disease (CVD). Weight loss reduces blood pressure in both hypertensive and non hypertensive overweight individuals, reduces serum triglycerides, increases HDL-C, and somewhat reduces total serum cholesterol and low density lipoprotein cholesterol (LDL-C). Weight loss reduces blood glucose levels in overweight and obese people with and without diabetes and can reduce glycosylated hemoglobin (HbA1c) in people with type 2 diabetes.

Metabolic Syndrome

• The American Heart Association and the National Heart, Lung, and Blood Institute recommend that the metabolic syndrome be identified as the presence of three or more of these components (specific to population; U.S. shown):

•Elevated waist circumference:

Men—equal to or greater than 40 in. (102 cm)

Women—equal to or greater than 35 in. (88 cm)

•Elevated triglycerides:

Equal to or greater than 150 mg/dl


http://en.wikipedia.org/wiki/Metabolic_syndrome

Metabolic Syndrome

•Reduced HDL (“good”) cholesterol:

Men—less than 40 mg/dl

Women—less than 50 mg/dl

•Elevated blood pressure:

Equal to or greater than 130/85 mmHg

•Elevated fasting glucose:

Equal to or greater than 100 mg/dl

Obesity is considered a disease, there is controversy about whether it is an independent cause of premature death or whether it is deadly because of the constellation of risk factors for mortality that accompanies obesity (Metabolic Syndrome)

Etiology of Overweight and Obesity: Set Point or settling Point?

• Two common theories about the etiology of overweight and obesity, set point and settling point, address how physical activity can play a role in the treatment or prevention of overweight and obesity.


Set Point Theory

• Set point theory hypothesizes that the body has an internal control mechanism, that is, a set point, located in the lateral hypothalamus of the brain, that regulates metabolism to maintain a certain level of body fat.

• Though evidence in rats has supported the theory, there is no scientific consensus that such a metabolic set point exists in humans for fat maintenance.


Settling Point Theory

• Weight loss and gain in most humans are more related to the patterns of diet and physical activity that people “settle” into as habits based on the interaction of their genetic dispositions, learning, and environmental cues to behavior.

• Evidence suggests that obese people are more sensitive to food-related stimuli in the social and physical environment, which influence their energy intake, than to the stimuli for energy expenditure


The Role of Physical Activity

• Physical activity has an important role in the prevention and treatment of overweight and obesity, even if that role is not yet completely understood.

• Prevention of obesity in children should focus on increasing vigorous physical activity rather than restricting energy intake

• Evidence shows that regular physical activity or physical fitness can (1) reduce health risks in people who are overweight, (2) protect against excessive weight gain, (3) help overweight and obese people lose weight, and (4) help people maintain stable weight after they lose it.


Physical Activity and Fitness and the Health Risks of Obesity: The Evidence• Physical Activity Studies on the joint association

of self-reported physical activity and high BMI typically show that each is an independent risk factor for all-cause mortality and mortality from CVD and cancer.

• The mortality risk of obesity is not eliminated by physical activity, but it was usually reduced substantially in population cohorts that did not initially have a chronic disease.



Physical Activity and Overweight or Obesity: The Evidence

Physical Fitness• Lipid Research Clinics Mortality Study• examined the prospective associations of fitness

and BMI with mortality risk in 1359 Russian men and 1716 U.S. men aged 40 to 59 years who were followed for 18 to 23 years

• fitness eliminated the risks of obesity in Russian men; but in American men, fitness and fatness were associated with mortality independently of each other



Physical Fitness• Aerobics Center Longitudinal Study

– Association of fitness with reduced risk of CVD and all-cause mortality was independent of overweight

– When all other variables were accounted for, fitness level was the determining factor for relative risk. BMI variance in each fitness category did not change the relative risk (see Figure 9.8, next slide)

Figure 9.8 - Aerobics Center Longitudinal Study with 21,856 men followed for approximately eight years. a total of 21,925 men aged 33 to 83 years were followed and men with abnormal ECG or history of myocardial infarction, stroke, or cancer excluded. results were adjusted for age, examination year, smoking, alcohol intake, and parental history of coronary heart disease



Physical Fitness• Women’s Ischemia Syndrome Evaluation

(WISE)• From 1996 to 2000, 936 women were enrolled at four U.S.

academic medical centers when clinical evaluation and angiography indicated they had myocardial ischemia At enrollment, 76% were overweight.

• Overweight women were more likely than normal weight women to have CAD risk factors, but BMI and girth measures were not associated with CAD or cardiovascular events after adjustment for other risk factors. Lower fitness scores at entry were 80% more likely to have CAD risk factors


Fit But Fat ?A recent large study using pooled data from 19 prospective

studies of 1.46 million white adults, 19 to 84 years of age, observed that after taking biases from smoking and ill health into consideration and adjusting for physical activity, there was a J-shaped relationship between BMI and all-cause mortality (Berrington de Gonzalez et al. 2010). The highest mortality rates occurred at BMI of 40.0 to 49.9 kg/m2 and the lowest generally at 20.0 to 24.9 kg/m2.

The evidence is clear that physical activity can favorably modify the impact of overweight and moderate obesity on several health risk factors, including metabolic syndrome

Physical Activity and Prevention of Excess Weight Gain: The Evidence

• A review of 11 prospective cohort studies concluded that physical activity or increased fitness measured by maximal treadmill endurance is associated with minimizing weight gain or with a reduction in the risk of large weight gains (e.g., 5-10 kg) among adults over periods ranging from two to 10 years

• The optimal amount of physical activity needed for weight maintenance (<3% change in body weight) over the long term is unclear, but that many people may need more than 150 min of moderate-intensity activity each week to maintain their weight at a stable level




• Finnish Cohort Study– Risk of weight gain (5kg) was elevated in

subjects with little leisure-time activity– The prevalence of obesity was inversely

associated with physical activity



• NHANES I Follow-up Study– A low-level of physical activity was strongly related to

major weight gain (13 kg)– The relative risk (RR) of major weight gain from the

lowest to highest fit group was 3.1 for men, and 3.8 for women

– The RR was 2.3 for men and 7.1 for women if they reported low levels of physical activity in both the initial and follow-up survey.



• Nurses Health Study– Those women who quit smoking and did not

change their physical activity levels gained 2.3 kg vs. those who continued to smoke

– Those women who quit smoking and increased their physical activity only gained between 1.3-1.8 kg (weight gain prevention).



• The Coronary Artery Risk Development in Young Adults (CARDIA) Study– Examined both men and women, white and black

adults.– Decreased physical fitness is strongly associated with

weight gain in both sexes– Each 1 minute decrease in maximal treadmill

endurance translated into 1.5 kg weight gain in men and 2.1 kg in women



• U.S. Male Health Professionals– Middle-aged men who increased physical activity lost

an average weight of 1.4 kg compared to a weight gain of 1.4 kg in the entire cohort.

– The prevalence of obesity was the lowest in those who maintained vigorous activity

– Each 1.5 hour increase in weekly vigorous activity predicted a 2-kg weight loss in middle-aged men


Physical Activity and Prevention of Excess Weight Gain: The Evidence• American Cancer Society: Cancer Prevention

Study I and II (see also Figure 9.9, next slide)• A cohort of healthy, non-Hispanic white men (n =35,156)

and women (n = 44,080) aged 50 to 74 years who had self reported BMI (kg/m2) of 18 to 32 were questioned in 1982 and 1992 about their weight and participation in 10 leisure time physical activities and home chores

• Smaller gains in BMI among men and women who were most active compared to inactive

• Protection of weight gain less among those who initially presented overweight


Figure 9.9 - Consistent leisure-time physical activity and 10-year body mass gain in normal-weight Americans.


Physical Activity and Prevention of Excess Weight Gain: The EvidenceStudy of Women’s Health Across the Nation (SWAN)• This was a prospective study of the associations of

weight and waist circumference with physical activity around the period of menopausal transition among 3064 racially and ethnically diverse U.S. women aged 42 to 52 years

• Maintaining or increasing physical activity levels helped protect against midlife increases in body weight and girth that women commonly experience.

Physical Activity and Prevention of Excess Weight Gain: The Evidence• Sweden Study• The association of moderate-to-vigorous exercise two or

more days a week with BMI was examined over eight years

• In both men and women, those who did not exercise had an increase in BMI

• Men who said they exercised at baseline but not at follow-up had a larger increase in BMI than men who exercised at both baseline and at follow-up.

• Women who did not exercise at either baseline or follow-up had an increase in compared to women who exercised both at baseline and follow-up.

Physical Activity and Prevention of Excess Weight Gain: The Evidence• Norway Nord-Trøndelag Health Study: HUNT 1

and HUNT 2 (see also Figure 9.10, next slide)• Longitudinal study of an entire county in Norway

examined whether leisure-time physical activity could predict change in BMI measured 11 years later

• Weight gain was greater among inactive men and women, but physical activity had a modest impact on slowing weight gain in healthy, normal-weight adults.


Figure 9.10 - Leisure-time physical activity and 11-year weight gain in normal-weight Norwegian adults.


Physical Activity and Prevention of Excess Weight Gain: The Evidence• Aerobics Center Longitudinal Study

– Change in fitness predicted weight gain or loss between repeat weight measurements over 7.5 yrs.

– Fitness reduced the risk of weight gain (10 kg) by more than 20% in both men and women

– Fitness reduced the risk of weight gain (5 kg) by more than 10 – 15 % in both men and women


Physical Activity and Prevention of Excess Weight Gain: The Evidence• The Framingham Children’s Study (FCS)• This longitudinal study of childhood cardiovascular risk behaviors

began in 1987 with a small cohort of 106 healthy children aged 3 to 5 years who were third- and fourth-generation offspring of the initial Framingham Study cohort.

• An eight year follow-up of 94 children found that boys and girls in the highest one-third of average daily activity from ages 4 to 11 years had smaller gains in BMI and skinfold thickness throughout childhood than the other children

• The difference was most pronounced in girls. By age 11, BMI was about 7% lower and skinfold thickness about 20% lower in the most active children.

Physical Activity and Prevention of Excess Weight Gain: The Evidence• American Indian Schoolchildren – PATHWAYS• A cohort of 454 American Indian schoolchildren was

followed for three years from 2nd to 5th grade• skinfolds and bioelectrical impedance were used to

estimate percent body fat• higher levels of total physical activity (recorded from

accelerometer counts) predicted lower percentage body fat by 5th grade among normal-weight children but not overweight children.

• Although an objective measure of physical activity was used in this study, it was performed for only one day of observation. Also, skinfolds, bioelectrical impedance, and BMI are imprecise measures of body fatness.


Physical Activity and Prevention of Excess Weight Gain: The Evidence• Avon Longitudinal Study of Parents and Children

(ALSPAC)• Ongoing birth cohort study with data collected between 2003 and

2007 that examined associations between children’s physical activity at age 12 and their body fatness at age 14

• Total and moderate-to-vigorous physical activity (measured by an accelerometer for seven days) at age 12 was predictive of body fat mass (measured by DXA) at age 14.

• An extra 15 min of moderate-to-vigorous physical activity per day at age 12 was associated with lower fat mass at age 14 in boys (by 11.9% [95% CI: 9.5-14.3%]) and girls (by 9.8% [6.7-12.8%]).

Physical Activity and Prevention of Excess Weight Gain: The Evidence• The Women’s Health Study (WHS)• The WHS was a randomized trial testing low-dose aspirin and

vitamin E for preventing CVD and cancer among healthy women, conducted between 1992 and 2004. A recent analysis examined the association of different amounts of physical activity with long-term weight changes among women consuming a usual diet.

• The findings from this large study with long follow-up provide support for the conclusion of the scientific advisory committee for the Physical Activity Guidelines for Americans—that many individuals may need more than 150 min of moderate-intensity activity each week to maintain their weight at a stable level

Physical Activity and Weight Loss: The Evidence

• It is paradoxical that at the same time the prevalence of obesity in the United States was increasing, more adults were engaging in voluntary weight loss

• A recent systematic, quantitative review evaluated 18 prospective cohort studies of mortality risk after intentional weight loss by change in diet or physical activity

• Fourteen of the studies adjusted for physical activity, but the studies did not clarify the relative contributions of diet or physical activity to weight loss or to mortality risk. The authors concluded that there was a need for well-designed studies to identify the independent and interactive effects of physical activity, diet, and body composition in populations most likely to increase longevity through weight loss.


Physical Activity and Weight Loss: The Evidence

• Weight Cycling: Aerobics Center Longitudinal Study (ACLS)

• Weight cycling status was defined as five or more episodes of losing at least 2.3 kg.

• Even though a history of weight cycling did not increase the risk of long-term weight gain, cardiorespiratory fitness at baseline and increased fitness over the follow-up were associated with less weight gain in both women and men

• For each extra 1 min of endurance on a maximal treadmill test at baseline, or for each 1-min increase in endurance between clinic visits (a difference of 7% in women and 5% in men), initial weight or weight gain was 0.2 kg lower for women and 0.55 kg lower for men.

Physical Activity and Obesity: The Evidence – Exercise Training Studies

• Although physical activity has great potential efficacy for reducing body fat mass, studies have found that its actual effectiveness is small.

• The American Dietetic Association recently concluded that few studies have used a large enough “dose” of physical activity to achieve a 5% weight loss with a physical activity intervention alone.

• There is emerging evidence, though, that regular physical activity can have favorable effects on abdominal obesity and excess fat stored in the liver and skeletal muscle when its effects on body weight or total fat mass are minimal



• Exercise ONLY• A recent meta-analysis evaluated 14 aerobic exercise

trials that lasted three to 12 months and involved 1847 obese or overweight patients. Six-month and 12-month programs similarly were associated with modest reductions in weight of 1.6 and 1.7 kg and waist circumference of about 2 cm

• Some other well-designed trials have shown benefits of exercise on abdominal obesity or have combined physical activity with diet for favorable weight-related outcomes.



• The Midwest Exercise Trial• 16-month randomized controlled trial tested

whether supervised, moderate-intensity exercise without dieting was effective for losing weight or preventing weight gain in young adults who were overweight

• Exercise prevented weight gain in women and produced weight loss in men. (see Figure 9-11, next slide)




Figure 9.11 Results of the Midwest Exercise Trial showed that 16 months of exercise reduced body weight and percent body fat without dieting in overweight men and women


• Fred Hutchinson Cancer Research Center—Seattle

• This 12-month trial examined the effect of moderate - to vigorous aerobic exercise in sedentary men and women

• Weight loss was less than expected, so the study shows that people tend to eat more when they exercise more, a practical problem of using exercise alone for short-term weight loss.


• Duke University—STRRIDE Trial• One hundred seventy-five sedentary, overweight men and women

(average BMI of 30 kg/m2) with dyslipidemia were randomly assigned to participate for six months in a control group or for eight months

• People in the control group had a 1% increase in body weight and an 8.6% increase in intra-abdominal fat, while the two exercise groups that expended about 14 kcal/kg each week had about a 1% decrease in body weight.

• The highest dose of exercise (i.e., about 23 kcal/kg each week) produced a nearly 3% decrease in weight and 7% decreases in intra-abdominal fat and subcutaneous abdominal fat without changes in caloric intake



• Minnesota Strength Training in Women Study• Sixty middle-aged women who had a BMI between 20 and 35 kg/m2

were randomly assigned to 15 weeks of twice weekly supervised strength training, followed by six months of unsupervised training, or to a no-intervention control group

• 39 weeks of follow-up, there was no effect of strength training on weight change, but the exercise group had changed the composition of their body weight (They gained 0.89 kg more fat-free mass, lost 1.0 kg more fat mass, and lost 1.63% more percent body fat compared to the control group who did not exercise.)

• This study shows not only that resistance training can be effective in helping women lose body fat but also why it is wrong to judge the effectiveness of exercise by body weight alone.



• University of Virginia• The effects of exercise training intensity on abdominal fat

and body composition were tested in 27 middle-aged obese women (BMI = 34 ± 6 kg/m2) with metabolic syndrome

• Women were assigned different exercise intensities• Computed tomography scans were used to determine

abdominal fat. Percent body fat was assessed by air displacement plethysmography.

• High-intensity training, but not low-intensity training, reduced total abdominal fat, subcutaneous abdominal fat, and intra-abdominal fat.

Physical Activity and Obesity: The Evidence – Exercise Plus Diet

• The scientific advisory committee for the Physical Activity Guidelines for Americans concluded that adults who want to lose more than 5% of their body weight through an exercise program must also keep their food intake constant or restrict it through diet (Physical

Activity Guidelines Advisory Committee 2008). Several studies have shown that this can be effective in people who are overweight or obese.



• Women’s Healthy Lifestyle Project• This was a five-year randomized controlled trial of a

dietary and physical activity lifestyle intervention• Women in the lifestyle intervention group were more

physically active and reported eating fewer calories than controls during the study period (see Figure 9.12, next slide).

• Percent body fat measured by skinfolds and DXA decreased by 0.5% in the diet plus physical activity group while increasing by 1% in the control group. Waist circumference decreased more in the intervention group than in controls.



Figure 9.12 The Women's Healthy Lifestyle Project showed that increased physical activity and decreased calorie intake prevented five-year weight gain in perimenopausal women


• St. Luke’s–Roosevelt Hospital, New York City• Moderately obese patients aged 19 to 48 years received weekly

nutrition counseling and were randomly assigned to one of three groups for eight months: diet plus strength training (progressive resistance for arms and legs), diet plus aerobic training (leg and arm cycling), or diet only

• All groups lost about 9.0 kg.• The strength training group lost less fat-free mass than the aerobic

and diet-only groups but nonetheless had a similar drop in RMR. Thus, strength training protected lean mass during dieting but did not prevent the decline in RMR commonly seen when overweight

people lose weight.

Physical Activity and Obesity: The Evidence – Behavioral Factors

• The Dose-Response to Exercise in Women (DREW) trial results showed that even though the exercisers were asked to keep their normal diet, most of the women who exercised ate more than they had before starting the trial.

• This illustrates the practical problems of gauging the impact of exercise on weight loss, as people may eat more than normal or decrease daily non exercise activities when they undertake a new exercise program.


Physical Activity and Obesity: The Evidence – Exercise and Appetite

• The brain senses blood levels of glucose and insulin and regulates hunger between meals. Low glucose stimulates appetite, while high levels of glucose and insulin inhibit appetite.

• Exercise lowers insulin and glucose levels, so it might affect appetite. Whether exercise stimulates or inhibits appetite in the short term has not as yet been clearly determined, but studies generally show that appetite is suppressed shortly after an exercise session



• “Leptin and ghrelin are two hormones that have been recognized to have a major influence on energy balance. Leptin is a mediator of long-term regulation of energy balance, suppressing food intake and thereby inducing weight loss. Ghrelin on the other hand is a fast-acting hormone, seemingly playing a role in meal initiation.” Source Article “The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review.” Physical Activity and Obesity

http://www.ncbi.nlm.nih.gov/pubmed/17212793




• High leptin levels induce feelings of satiety via the hypothalamus.

• Obese have high levels of circulating leptin but appear to be leptin resistant. Levels return to normal following weight loss

• Ghrelin is secreted by the stomach and pancreas to stimulate appetite, and increases before, decreases after meals. Ghrelin is increased after long duration exercise



• Suppression of appetite by these hormone activities seem to be more effective in men than women, based on a limited number of research studies.

• Women’s feelings of hunger were suppressed during a session of walking that expended 550 kcal, but they were not affected between meals despite an increase in ghrelin and a delayed and short-term decrease in leptin after exercise


Physical Activity and Obesity: The Evidence – Genetic Factors

• An association has been found for the FTO (see

section on “Association with Obesity”) gene. People of European ancestry who inherit a risky variation in the FTO gene from one or both parents (30-50% of the populations studied) weigh on average 1 to 4 kg more and have a 15% to 65% increased risk of having high BMI, perhaps because the gene contributes to eating more or storing more fat.


http://en.wikipedia.org/wiki/FTO_gene

Physical Activity and Obesity: The Evidence – Genetic Factors

• The population attributable risk of obesity from variations in the FTO gene has been shown to be about 20%

• Physical activity has been associated with lower BMI in people who have a risky version of the FTO gene in several studies, but not all.

• Despite the likelihood that physical activity will interact with people’s genes to influence obesity-related outcomes, some studies seem to show that physical activity habits during adulthood influence obesity just as strongly as, or more strongly than, genetic inheritance or childhood habits.

• Persistent physical activity reduces odds of weight gain even after genes and childhood environment are partially controlled.

Physical Activity and Obesity: The Evidence – Calories, Exercise

• The amount of weight loss with physical activity is additive to the loss that follows a reduction in calorie intake with a diet.

• Because physical activity, especially resistance exercise, can decrease the percentage of body mass that is fat while increasing fat free mass, it has the potential to retard the reduction in BMR common during restrictive diets.

• Exercise can lead to a small gain in fat-free mass as body fat is reduced; this occurs when body weight does not change during the exercise program.

Physical Activity and Obesity: The Evidence – Calories, Exercise

• People who desire to increase or maintain fat-free mass during an exercise program must have a diet of sufficient calories to balance the increased energy expenditure.

• In one study of obese women (You et al. 2006), only diet plus exercise, not diet alone, decreased the size of subcutaneous fat cells in the abdomen, a risk factor for type 2 diabetes.

Physical Activity and Obesity: The Evidence – Weight Maintenance

• Lost body weight is usually regained when diets are used alone, but diet combined with increased exercise seems to yield better maintenance of weight loss, especially if the exercise program is maintained after the diet ends.

• Figure 9.13 (next slide) illustrates the results of an eight-week diet among obese adults. Not only was exercise as effective as diet for weight loss, but adding an exercise program at the end of the diet also prevented participants from regaining weight eight and 18 months later.



Figure 9.13 Study on moderately obese people illustrates not only that exercise was as effective for weight loss as an eight-week diet among adults, but also that adding an exercise program at the end of a diet prevented participants from regaining weight later.


• The amount of physical activity needed to keep weight off after a diet is not fully known, but experts have suggested it may be as much as 2500 to 2800 kcal/week, two to three times as much as recommended for reducing other health risks

• Many correlation studies show a strong association between physical activity at follow-up and maintenance of a weight loss

• much of the lost weight is regained after exercise interventions end, and a high level of daily physical activity may be necessary to prevent weight regain


Strength of the Evidence

• Both population-based epidemiological studies and clinical trials support the claim that regular physical activity and exercise training are useful for reducing the primary and secondary risk of excess weight gain during adulthood and for helping obese or overweight people keep off most of the weight they lose after a weight loss intervention.



• Temporal Sequence– An increase in physical fitness (defined as an

increase in treadmill time) predict weight loss or stopping weight gain over periods of 2-10 years



• Strength of the Association– Expending 1,100 kcal/wk show mean

reductions of 0.06 kg (0.13 lbs) of fat weight per week.

– Expending 2,200 kcal/wk show mean reductions of 0.21kg (0.46 lbs) of fat weight per week.

– Thus, higher energy expenditures are associated with greater fat loss.



• Consistency– Exercise training contributes to weight and fat

loss in both men and women regardless of race

– Physical activity and fitness level also reduce mortality risk in people who are overweight.


Strength of the Evidence –

• Dose Response– Fat loss is linearly dependent on the amount

of energy expenditure in short term studies– This finding is not reproducible in long term

studies because of poor subject adherence to exercise

– Effective exercise programming would include long duration (60 + minutes of walking) and high caloric expenditure (2000 kcal /week) at 55% or higher intensity



• Biological Plausibility– Energy expenditure can be increased up to 20

times basal metabolism during exercise, promoting a negative energy balance

– Depending upon the intensity of exercise, post-exercise energy expenditure may increase

– Increasing lean mass will increase BMR, exercise helps to maintain lean mass.


• Biological Plausibility• Resistance exercise training can increase basal

metabolic rate by an extra 50 to 75 kcal on average. Most of the increase is explained by increased nonfat body mass, not by extra use of protein as fuel.

• Increased physical activity and better nutrition have been shown to normalize glucose and lipid blood profiles in the absence of significant weight loss in many individuals.

How Does Exercise Help People Lose Body Fat?

• Increases energy expenditure • Retards loss of muscle mass, hence

maintaining BMR • Increases metabolic rate during and after

exercise • Possibly increases SNS activity in people

who have abnormally low tonic activity of the sympathetic nervous system

How Does Exercise Help People Lose Body Fat?

• Possibly suppresses appetite acutely after exercise, though overall appetite tends to increase with chronic increases in physical activity

• Offsets effects of weight cycling (yo-yo dieting)

• Has positive psychological effects that help people adhere to dietary or exercise programs

Final Thoughts

• Weight Loss or risk reduction? Most individuals judge the success of diet and exercise by scale weight. Rates of weight loss with a successful program average approximately 1 kg per week, which is viewed by many as frustratingly slow progress. Hence, dropout rates can be high within the first three to six months of a weight loss or exercise program. A change from preoccupation with scale weight to healthful management of blood pressure, blood glucose, and blood lipid levels through a prudent diet and regular physical activity in pursuit of moderate physical fitness is perhaps a more important health goal for most people who are overweight but not obese.


End of Presentation

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=WbKURRH7pch4xM&tbnid=fbfaxI8iBNwtjM:&ved=0CAUQjRw&url=http://www.hivehealthmedia.com/television-obesity/&ei=sklbUdbQAYr88QTJ7IDABw&bvm=bv.44697112,d.eWU&psig=AFQjCNHVvKco5oWsa7HKQ6omtjnc_jqF_w&ust=1365023371328323

chapter 09 physical activity and obesity. definitions: obesity: having a very high amount of body...

Documents

obesity slide

prevalence of obesity

prevalence equal

cdc obesity trends

adults brfss

prevalence estimates

states mississippi

adults weight