A Weighty ProblemWeight gain has become a worldwide pandemic. Between 1975 and 2016, the prevalence of excess body weight in adults increased from nearly 21% in men and 24% in women to approximately 40% in both sexes. Adiposity-based chronic disease (BMI ≥ 30 kg/m2) quadrupled in men, from 3% to 12%, and more than doubled in women, from 7% to 16%. This has resulted in a more than 6-fold increase in the number of adults afflicted by weight gain worldwide, driven largely by changes in the global food system, promoting the marketing of calorie-dense, nutrient-poor foods, coupled with reduced physical activity. (Sung et al, 2019) More of the earth's population now suffers from too much food, rather than from lack of food. This has resulted in an increasing number of overweight persons. This is a problem even amongst children. A multitude of health complications occur from adiposity-based chronic disease, including cardiovascular disease, diabetes mellitus, chronic kidney disease, cancers, and musculoskeletal disorders. (Dai et al, 2020) Adiposity-based chronic disease reduces life span. Compared with persons of healthy weight, life expectancy from age 40 years is 4.2 years shorter in obese (BMI ≥30) men and 3.5 years shorter in obese women. (Bhaskaran et al, 2018) Why is it difficult to avoid gaining weight, to lose weight, and then to keep the weight off? Human biology favors storing excess food as fat as a reserve when food is scarce. Throughout human history, until recently, food sources were intermittent and scarce. With plentiful food sources and with constant marketing of food products, but the same biology, we now often consume more than we need. Highly processed foods (in a can, bag, or bottle) are addictive substances, similar to tobacco products. (Gearhardt and DiFeliceantonio, 2022) Losing weight and keeping the weight off are challenging. Following successful weight loss there are biologic and physiologic changes driving weight regain. The hormone leptin produced by body fat and signaling satiety becomes reduced following weight loss, leading to both a sense of hunger as well as a reduction in resting energy expenditure. Weight loss leads to an increase in the hormone ghrelin released from the stomach, signaling hunger. These effects drive desire for increased food intake. (Rosenbaum et al, 1997) Successful weight loss and keeping the weight off occur with both diet modification and increased physical activity. Motivation to do so is challenging. People who are more successful at maintaining weight loss have high levels of physical activity, low calorie and fat intake, high levels of restraint, and low levels of disinhibition (a tendency toward over-eating and loss of control). (Thomas et al, 2014) What drives increasing weight? The formula is simple: Food eaten Energy expended = Weight GainedAnother way of explaining the situation: Delicious, Calorie Dense Food + Sedentary Lifestyle = Weight GainMost people live in a food toxic environment and are bombarded by cues to buy and eat food throughout the day. In addition, stress drives overeating. (Yau and Potenza, 2013) Stress + Abundant Food = AdiposityWeight status can be measured by calculating the body mass index, or BMI, as follows: Body Mass Index = weight in kg / height in meters2 One's beliefs about food and diet affect the BMI. People who implicate insufficient exercise as a cause for Adiposity-based chronic disease tend to consume more food and have a higher BMI than people who believe adiposity is caused by a poor diet. (McFerran and Mukopadhyay, 2013) The aggressive marketing with increased availability, accessibility, and affordability of calorie-dense foods drives weight gain. (Dai et al, 2020) Processed foods can be designed to have combinations of saltiness, sweetness, and texture (from fat content) that achieve a "bliss point" of taste sensation. This sensory input goes to reward centers of the brain to drive craving for further food consumption, past a point of satiety. Reward center stimulation of the brain can bypass the executive function (judgment) of the brain to control food consumption. The salt and sugar will increase preservation and shelf life of processed foods as well as mask additive chemicals found in packaged and canned food products. (Gottfried, 2011) There is ordinarily a modest amount of calories used for energy to maintain normal body metabolic processes, called resting energy expenditure. In general, for a normal healthy adult to maintain body weight with just activities of daily living, caloric intake must be limited to 10 calories (kcal) per pound (22 calories per kg). Thus, a 150 lb (68 kg) person needs about 1500 calories (kcal) per day to avoid gaining weight. Exercise can increase caloric use, and exercise has a "carryover effect" to increase metabolism and use more calories after exercise. Of course, growing children require more calories. (Willett et al, 1999) Exercise can burn calories (average for a standard 70 kg person) as follows:
Health Promotion
Just brisk walking for 20 minutes a day can have major benefits. A good aerobic exercise with cardiovascular benefit is to climb 10 flights of stairs once a day. Increase by one flight per week to achieve the goal. Physical activity, with more at least of moderate intensity, is associated with lower rates of cardiovascular disease in both men and women. (Dempsey et al, 2022) Young adults can generally eat more and not gain weight because they have higher resting energy expenditure, but metabolism tends to slow in the mid-30's (and middle-aged people become more inactive), so many adults gradually gain weight. One pound (0.45 kg) of fat has 3500 kcal. An excess intake of only 0.3% of calories eaten translates into a 20 pound (9.1 kg) weight gain over the age range of 25 to 55 years. The average weight gain in young adults averages 0.2 to 0.8 kg per year. The body mass index (BMI) may be related to multiple genetic factors in 30 to 40% of persons, and this may in part determine the pattern of body fat distribution. Single gene defects that produce a defined disease marked by adiposity, such as the Prader-Willi syndrome, are rare. (Rosenbaum et al, 1997) Food intake is regulated via neural circuits located in the hypothalamus. A hormone produced in adipocytes (fat cells) known as leptin has the function of informing the hypothalamus about the state of fat stores. Increased leptin inhibits food intake and increases energy expenditure. Differences in leptin levels may explain differences in BMI. (Rosenbaum et al, 1997) Social factors play a major role in weight gain. Situations during life in which weight gain is more likely to occur include: adolescence, pregnancy, mid-life in women, and following marriage in men. Persons who emigrate to a more urbanized culture tend to gain weight. Behavioral or environmental changes in life, such as smoking cessation, are associated with weight gain. Weight gained during holiday periods and festivals is more than at other times of the year and tends not to be lost. (Yanovski et al, 2000) The chance of becoming obese increases by 57% if one has a friend who becomes obese in a given interval. Among pairs of adult siblings, if one sibling becomes obese, the chance that the other becomes obese increases by 40%. If one spouse becomes obese, the likelihood that the other spouse becomes obese increases by 37%. (Christakis and Fowler, 2007) Adopting a healthy diet and exercise program is part of an overall health promotion strategy. This is part of preventivie medicine. The ten words of prevention:
Preventive measures can influence the level of cardiovascular health, which has a bearing on life expectancy free of major chronic disease, not only cardiovascular disease but also diabetes mellitus, cancer, and dementia. This level can be estimated via the American Heart Association’s Life’s Essential 8 score based upon the following patterns of behavior: (Wang et al, 2023)
What are the Risks?An ideal body mass index (BMI) is in the range of 20 to 24 and anything above or below that range will increase certain risks for morbidity and mortality. In general, a BMI >28 increases the risk for morbidity. A third of the U.S. adult population qualifies as obese, defined with a BMI of 30 or more, while hlaf are defined as overweight by a BMI 25 or more. (Note: this tutorial's author's BMI is 20) However, the distribution of fat has importance in determination of risk. A central distribution of fat, as is more typical of men, carries a higher risk for morbidity. A more peripheral distribution, as in hips and thighs in women, carries a lesser risk. The risk can be determined by measuring waist circumference and by calculating a waist-to-hip circumference ratio. In general, a waist:hip circumference ratio >0.9 for men and >1.0 for women carries an increased risk for morbidity. (Pischon et al, 2008) Another risk is the time of onset of adiposity, which in childhood increases the risk for morbidity, regardless of whether adiposity persists into adulthood. Risks for morbidity are increased as follows when the BMI is 26, versus 21:
Specific Health Risks with Adiposity-based Chronic DiseaseThere are some diseases that are seen with increased frequency in persons with high BMI, including those who are obese. Cardiovascular disease, diabetes mellitus, kidney disease, and cancer account for the greatest amount of death and disability with high BMI. Additional health problems include hypertension, stroke, metabolic-associated steatotic liver, osteoarthritis, reproductive problems, sleep apnea, and gallbladder disease. (Dai et al, 2020) The worldwide COVID-19 (SARS-CoV-2) pandemic starting in 2020 is related to multiple co-morbidities, including adiposity. People with diabetes mellitus, adiposity, cardiovascular disease, and hypertension are more likely to get infected and are at a higher risk of mortality from COVID-19. Obese persons are at higher risk of developing complications from SARS-CoV-2. (Abu-Farha et al, 2020) CancerIn 2012, it was estimated at 544,300 cases, or 3.9% of all cancers worldwide, were associated with excess body weight. (Sung et al, 2019) The following cancers are seen with increased frequency in persons who are overweight: (López-Suárez, 2018)
Diabetes Mellitus and Metabolic Syndrome (Pre-Diabetes)The global pandemic of adiposity-based chronic disease has led to a marked increase in the number of persons worldwide with metabolic syndrome. Both type 2 diabetes mellitus and metabolic syndrome share common features, and patients may be defined as having one or both. (Eckel et al, 2010) A characteristic pathologic finding in the islets of Langerhans of the pancreas can be seen in association with type II diabetes mellitus. A major complication of diabetes mellitus results from the accelerated, advanced atherosclerosis.
Coronary Artery DiseasePersons with diabetes mellitus are at increased risk for accelerated and advanced atherosclerosis that increases the risk for coronary artery disease that can lead to myocardial ischemia and myocardial infarction. However, even obese persons who do not have hyperglycemia can have an increased risk for coronary atherosclerosis. Obese persons have a >50% risk for a total serum cholesterol >250 mg/dL. In contrast, a study of middle-aged women revealed that those who did not smoke, were not overweight, maintained a healthy diet, and exercised at least moderately for a half hour each day had an incidence of coronary events 80% lower than the rest of the population. (Stampfer et al, 2000) Atherosclerosis is potentially reversible. Adoption of major lifestyle changes including diet and exercise even in adults can lead to reduced risk for coronary artery disease. (Spring et al, 2014) Hypertension and StrokePersons who are obese tend to have an increased blood pressure. Hypertension that is untreated can increase the risk for heart failure, kidney failure, and stroke. The rate of ischemic cerebrovascular disease is higher in women with a BMI >27 and 137% higher in women with a BMI >32, compared to women with a BMI persons with a higher BMI. The prevalence of cardiovascular diseases and their complications increases as the amount of dietary sodium increases. It is estimated that if adults from 40 to 85 years of age in the U.S. were to decrease sodium intake by just 9.5%, there would be 1 million fewer deaths and $32 billion saved in health care costs over their lifetime. (Smith-Spangler et al, 2010) CardiomyopathySome obese patients who have little or no coronary artery disease and do not have a history of hypertension may still develop heart failure. In these patients, the heart is globally enlarged, similar to a dilated cardiomyopathy. If such persons lose weight, the heart diminishes in size. This adiposity-based cardiomyopathy may be related to blood volume expansion or other factors. (Alpert et al, 2016) Metabolic dysfunction–associated steatotic liver disease (MASLD)MASLD is being recognized more frequently. Dietary patterns play a role in the development of steatosis (fatty change) in the liver. Adiposity increases the risk for alterations in hepatocyte function that lead to accumulation of lipid in hepatocytes and hepatomegaly. MASLD reduces the metabolic function of the liver. MASLD can proceed to Metabolic dysfunction–associated steatohepatitis (MASH), to liver failure, and even cirrhosis, with an increased risk for development of hepatocellular carcinoma. (Choudhury and Sanyal, 2004) When combined with alcohol intake, the risk for advanced liver disease is much greater. (Ntandja Wandji LC, et al, 2020) OsteoarthritisIncreased weight will increase the stress on weight-bearing joints from a variety of factors. Osteoarthritis most often affects lower extremities. (Nedunchezhiyan et al, 2022) Reproductive ProblemsWomen who are obese are more likely to have menstrual irregularities and ovulatory infertility, including the polycystic ovarian syndrome (PCOS). Women with PCOS typically have irregular bleeding, hirsutism, and/or infertility in association with chronic anovulation and androgen excess not attributable to another cause. There is an increased prevalence with diabetes mellitus and adiposity. PCOS is characterized by insulin resistance, hyperandrogenism, and abnormal gonadotropin release with inadequate follicle stimulating hormone release, leading to anovulation. Weight loss aids in treatment of PCOS. (Trikudanathan, 2015) Adiposity in women who are pregnant increases the likelihood for gestational diabetes that can affect the developing fetus. Maternal adiposity increases the risk for macrosomia, stillbirth, and neural tube defects. The increased maternal risks include hypertension, pre-eclampsia, and hemorrhage. (Dixit and Girling, 2008) Adiposity-based Hypoventilation SyndromePersons who are obese have a greater likelihood for obstructive sleep apnea (OSA), or periods of absent breathing while asleep. OSA is the major feature of adiposity-based hypoventilation syndrome, which is defined by a body mass index ≥ 30 along with sleep-disordered breathing and chronic daytime alveolar hypoventilation with PaCO2 ≥ 45 mm Hg. Persons who snore while sleeping have a propensity to develop sleep apnea. The increased soft tissue in upper airways contributes to the problem. Sleep apnea is accompanied by decreased ventilation (hypoventilation) and pulmonary dysfunction. (Iftikhar and Roland, 2018) Gallbladder DiseaseBiliary tract lithiasis, manifested mainly by development of cholelithiasis (gallstones), is more likely to occur in persons who are obese. The gallstones are typically of the mixed type with cholesterol. Cholelithiasis can lead to cholecystitis and to pancreatitis. (Sun et al, 2022) What Can Be Done?exercise will prevent adiposity from happening. Losing weight once it has been been gained is difficult, but worth trying for health benefits.National PolicyWhat nation has experienced a marked reduction in coronary artery disease over the past 40 years? Finland. Mortality from ischemic heart disease remained high following World War II. The North Karelia Project began in 1972 as a community-based intervention to influence diet and other lifestyles needed to prevent coronary artery disease. This project was subsequently adopted nationally. Ischemic heart disease mortality in a working-age population declined by 73% in North Karelia and by 65% in the whole country from 1971 to 1995. The project utilizes low-cost intervention activities with widespread participation through community organizations as well as national policies. (Papadakis and Moroz, 2008) In addition, interventions to reduce salt intake were undertaken in Finland (reduce salt content in food processing, label food product contents, and promote educational campaigns) with the result that the average systolic and diastolic blood pressure measures declined by more than 10 mm Hg over 30 years, with a 75 to 80% decrease in deaths from stroke and coronary artery disease. (Aaron and Sanders, 2013) DietsIf you diet, your body adapts to the lower caloric intake and becomes more efficient at utilizing and storing as fat any calories taken in. Thus, if you go off the diet, you gain weight even faster than before. The best diet is the one you continue to follow. Legitimate weight loss programs incorporate lifestyle changes that have more longer-lasting effects. (Sacks et al, 2009) Dieting is more frustrating for women. Since women average twice as much body fat as men, women will tend to gain weight twice as fast, or lose weight half as fast, as men. Thus, when husband and wife adopt a new diet to lose weight, the advantage is seen more quickly by the husband. The wife needs more encouragement and dedication. Consumption of foods recommended in current dietary guidelines is associated with decreased risk of mortality for both men and women. (Kant et al, 2009) What about "low carbohydrate" diets? Like many popular myths, this diet does have a shred of reality behind it, based upon "specific dynamic action" (SDA) of foods, or the amount of calories required just to digest, absorb, and metabolize the food. More complex proteins and fats require more energy to process, up to 30% of calories in proteins and up to 10% in fats, while simple carbohydrates require only 5%. The average diet takes about 10%, and this is part of the basal metabolic rate. Thus, one could eat a just little more protein or fat and increase the total calories consumed, without weight gain. However, these differences in SDA are not marked. If total calories are reduced, particularly from carbohydrates, lipolysis and ketosis with acidosis occur. (Sacks et al, 2009) (Goldenberg et al, 2021)
The "glycemic index" (GI) is a measure of the ability of foods to raise the blood sugar and stimulate insulin release via the the rate of carbohydrate absorption after a meal. Many factors together, including carbohydrate type, fiber, protein, fat, food form and method of preparation, determine the GI of a particular food. Low GI foods such as complex carbodydrates that take longer to digest are associated with decreased return of hunger and a lower blood glucose. Sugar, obviously, has a very high GI, while a salad would have a low GI. (Rosenbaum et al, 1997) The type of food eaten in a diet is not as important as just reducing overall intake. Adherence to a weight loss program requires a plan with self-efficacy, knowledge, and motivation at the beginning of a weight-loss program and explore behavior-specific strategies to improve knowledge and self-efficacy. (Leung et al, 2019) Pharmacologic and Surgical TherapiesAmericans are enfatuated with "quick fixes", fads, and pill-popping, so a popular approach to weight loss is the infamous "diet pill". Weight tends to be gained with cessation of the drug use. Both drug and surgery strategies have been applied to interventions for adiposity. Recommendations include treatment for patients with a BMI ≥ 30 or a BMI 27 to 30 with weight-related comorbidities if unable to lose or maintain weight loss using lifestyle interventions. Bariatric surgery may be considered with a BMI ≥ 40 or a BMI ≥ 35 with weight-related comorbidities. Such therapies are recommended in conjunction with a lifestyle intervention. (Reid and Korner, 2022) References
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