In perfect shape or not, we decide for ourselves. The perception of obesity has seen extraordinary changes in the historical development of humanity. In the Middle Ages, it was seen as an expression of high social status, and later as a rare aesthetic problem. Nowadays, however, because of the health risks it poses and the continuous increase in its frequency, it is defined as one of the most serious metabolic disorders. Here’s what you need to know about it.
What is obesity?
Obesity can be defined as an increase in body weight expressed in abnormal deposition of triglycerides in fat depots with a marked negative effect on the body. Since accurate measurement of the amount of fat tissue in the body requires expensive and difficult to obtain tests, a single method of determining the degree of obesity, the so-called body mass index (BMI), has been introduced into health care practice. Described in 1896 by A. Quételet, BMI is the ratio of body weight in kilograms to height in metres squared (BMI = kg/m2).
In 1997, the World Health Organization (WHO) adopted a standard to classify body weight according to BMI (Table 1) (1). However, this index does not provide any information on the amount of fat tissue and, more importantly, where it is located in the body. The regional distribution of adipose tissue is an extremely important aspect of obesity, determining the frequency and seriousness of coexisting or co-occurring diseases. The accumulation of adipose tissue in the abdominal region, known as android fat distribution (central, male-type) obesity, is associated with a significantly increased health risk compared with gynoid (pear-shaped, female-type) obesity. For this reason, BMI determination is most often accompanied by a waist circumference measurement. A BMI ≥ 25 kg/m2 combined with a waist circumference ≥ 102 cm in men and ≥ 88 cm in women has been shown to dramatically increase the likelihood of developing complications such as: hypertension, dyslipidaemia (abnormal blood lipid profile), atherosclerosis, insulin resistance, type 2 diabetes mellitus, stroke and heart attack. (2)
The rate of obesity is rising at an extremely fast pace worldwide, reaching epidemiological proportions. According to official statistics, 270 million of the world’s population are currently diagnosed as obese and 1.2 billion as overweight, with the trend being for these figures to reach 750 million and 2.5 billion respectively by 2024. Even more alarming are the facts that the number of obese children under 5 years of age exceeds 5 million and that the prevalence of morbid obesity grade III (≥ 40 kg/m2) has increased about 6-fold in the last decade (3).
Across Europe, overweight affects about 50% and obesity about 20% of the population, with Central and Eastern Europe among the most affected regions. (4)
The country with the highest prevalence of obesity in the population is the Micronesian Republic of Nauru – 85% in men and 93% in women.
What causes obesity to develop
Obesity is a metabolic disorder of a chronic nature, the result of complex interactions between endogenous (genetic features, hormonal balance) factors and the external environment. The main reason for its development is the prolonged maintenance of a positive energy balance due to increased energy intake, decreased energy expenditure or a combination of both. Since the main source of energy for the human body are nutrients, and energy expenditure is primarily associated with physical activity, let us consider these factors more closely.
Nutrition in the etiology of obesity
If until a few decades ago there were doubts about the importance of nutrition in the cause of obesity, today it has been proven without a doubt that dietary intake is central. Tracking dietary habits shows that energy intake has increased dramatically over the last 30-40 years, with a trend to continue increasing in the future. In addition, this quantitative change has been accompanied by qualitative changes in diet. Fat intake has increased dramatically, with beneficial mono- and polyunsaturated fatty acids giving way to atherogenic saturated fatty acids. At the same time, there has been a ‘spike’ in the intake of simple sugars, while the consumption of complex carbohydrates and fiber has declined (5). Foods rich in fat and simple carbohydrates are preferred for consumption because of their better palatability. At the same time, they have a low satiety effect and increased energy density (calories per unit weight), factors that easily induce a positive energy balance and consequently obesity.
The importance of physical activity
The constant economic growth, the rapid pace of industrialization and urbanization have minimized the need to perform activities requiring physical effort. If our ancestors were paid to perform physical work, we must pay to go to modern gyms and sport facilities, and exercise. Movement is a must for maintaining the normal structure and function of almost all the systems and organs in our body and it is logical that its absence causes pathological changes in them.
Numerous epidemiological studies have shown that sedentary lifestyle is associated with an increased frequency of metabolic disorders and in particular overweight and obesity. Interestingly, the relationship between reduced physical activity and obesity is bidirectional, i.e., lack of exercise leads to weight gain and overweight people are less likely to be encouraged to take up physical activity. Thus, the accumulation of excessive weight is exacerbated and leads to the formation of a vicious cycle.
The question of whether increased energy intake or reduced physical activity is the root cause of the observed spike in the prevalence of obesity today remains unanswered. Overeating is thought to have a greater impact because it is easier to induce a positive energy balance than to compensate with physical activity.
However, as I already mentioned, obesity is a consequence of complex interactions between internal and external factors. Let’s pay some attention to the former.
Is obesity a genetic inheritance?
Although obesity undoubtedly has a genetic component, the exact mechanisms behind it are not fully understood. Genetic influences are difficult to differentiate because in a very large number of cases the genotype is influenced by external, non-genetic factors. There are cases in which certain families and even ethnic groups are significantly more prone to obesity, but it is difficult to say that it is 100% inherited because these groups of people have identical eating and exercise habits.
Studies conducted among large groups of people with wide variations in BMI and amount of fat tissue, as well as among identical twins, show that 40 to 70% of individual differences are genetically determined. Genetic factors have also been found to influence mainly energy intake and to a lesser extent energy expenditure and nutrient absorption. At present, despite scientific progress, it is difficult to say with certainty whether obesity is genetically linked. (6)
The importance of certain hormones
In 1994 it was established that fat tissue is its own endocrine organ. The isolation of the hormone leptin (from the Greek leptos – weak) gave extraordinary hopes for the discovery of a medicine against obesity and caused a large number of scientists to start searching for other similar peptides.
Leptin is a peptide hormone secreted by fat tissue, and its circulating levels are proportional to its amount. Leptin acts on specialized receptors located in the hypothalamus and signals that the body has taken in enough food. So far, one mutation in the gene responsible for leptin production is known. Individuals suffering from this mutation have low circulating leptin levels, experience a continuous need for food intake and develop morbid obesity. External administration of leptin in these individuals has an extremely beneficial effect. Significantly more often, however, severely obese patients possess high serum leptin levels and a simultaneously severely increased appetite. In these cases, leptin resistance is involved and replacement therapy has no effect (7).
Ghrelin is a hormone secreted in the gastrointestinal tract, possessing an action antagonistic to that of leptin, i.e. it has been defined as a hunger hormone. Its levels are high when feeling hungry and before food intake and drop immediately after feeding. The action of ghrelin has been used to develop a vaccine against obesity that prevents it from reaching receptors in the central nervous system and signaling feelings of hunger (7).
Peptide YY (PYY) is another hormone relevant to appetite. Produced in various parts of the small and large intestine after feeding, it slows gastric emptying, thereby improving digestion and nutrient absorption and increasing feelings of satiety. People suffering from obesity have lower levels of PYY. Intake of protein-rich foods or beverages has been found to increase PYY secretion and prolong the feeling of satiety (7).
Adiponectin is another hormone produced in adipose tissue with potential influence on the development of obesity. Although its role has not been fully investigated, it has been proven that obese patients have low levels of adiponectin and vice versa – after lowering body weight, adiponectin concentration increases. Experiments conducted on laboratory mice showed weight loss after external administration of adiponectin. However, many more questions need to be answered before human trials can be conducted (7).
Why obesity is such a significant disease?
The social significance of obesity is determined not only by the threatening proportions it reaches in the world population, but also by the health risks it poses. The link between overweight, obesity and premature mortality is undeniable. Furthermore, obesity is a leading aetiological factor in the pathogenesis of a huge number of diseases that affect the world’s economically active population and lead to disability and loss of work capacity. According to official data, about 7% of total health expenditure in some developed countries is devoted to treating the effects of obesity. In reality, this figure may be many times higher because many of the diseases indirectly related to obesity are probably not included in the calculations (4). Here are some of the most common diseases caused by obesity, together with the