The relationship between fat, protein, sugar and obesity, and the influence of insulin-like sex hormones
IV. The Relationship Between Fat and Obesity
Lipids in the human body are divided into two parts: fats and lipids. Fats, also known as true fats, neutral fats, and triglycerides, are composed of one molecule of glycerol and three molecules of fatty acids. Fats are further divided into unsaturated and saturated types. Animal fats are predominantly composed of saturated fatty acids and are solid at room temperature. Conversely, vegetable oils are predominantly composed of unsaturated fatty acids and are liquid at room temperature. Lipids include cholesterol, phospholipids, and lecithin. In summary, fats serve as a storage depot for energy in the body, primarily providing heat; protecting internal organs and maintaining body temperature; assisting in the absorption of fat-soluble vitamins; and participating in various metabolic activities of the body, among others.
While fat has many functions and roles, its amount in the body is limited. Excessive fat can affect metabolic activities and lead to various diseases. This is why it's often said that "obesity is a breeding ground for disease." So, what range of fat content is considered normal, and how much constitutes obesity? Generally speaking, the degree of obesity is directly proportional to the increase in fat content. Of course, we have also observed some patients with localized obesity (such as abdominal obesity) whose fat content is not particularly high in their overall weight, but that amount of fat is enough to make them "inconvenient to move around." On the other hand, the slightly thicker fat in the chest, abdomen, and buttocks of fully developed women makes them look voluptuous and attractive. Therefore, it can be said that increased fat is not necessarily a terrible phenomenon. Unfortunately, excessive fat does bring many problems to obese people, such as inconvenience in movement, heat intolerance, affecting body shape, easy fatigue, and susceptibility to various diseases, etc. Therefore, we should indeed be determined to get rid of that excess fat from our bodies.
V. The Relationship Between Protein and Obesity
As we all know, protein is a "good thing," and it is comprehensively introduced as an important topic in nutrition journals and publications. Dietary recommendations suggest that each adult needs to consume approximately 30-45 grams of protein daily to ensure normal bodily function. So, what is protein? What are its functions? And why is it important to consume a certain amount daily?
In biology, proteins are defined as substances formed by amino acids linked together by peptide bonds to form polypeptides, and then by polypeptides linked together to form other substances. In simpler terms, they are the framework and main building blocks of human tissues and organs, playing a vital role in human life activities; it can be said that life would not exist without protein. Protein in our daily diet is mainly found in lean meat, eggs, beans, and fish. The amount of protein is not inherently related to obesity, because generally speaking, protein and fat do not interconvert. However, protein is constantly used in daily metabolism, and the amount used is relatively stable. If intake is insufficient, a person will noticeably lose weight. We know that any muscular person has relatively little subcutaneous fat tissue. This is because developing muscles requires relentless exercise, which results in fat loss and muscle strengthening; and also because the subcutaneous fat thickness is low, allowing the developed muscle tissue to be visible. Therefore, even if some highly muscular individuals (such as bodybuilders) exceed their ideal weight by 20%, they cannot be considered obese. In other words, obesity is only a relative excess of fat tissue.
VI. The relationship between sugar and obesity
Sugar is an important component of the human body. Although it only accounts for 2% of body weight, the amount of sugar we ingest from food is far greater than that from protein and fat. Therefore, sugar is the body's main energy source; under normal physiological conditions, about 70% of our energy comes from sugar.
So, what is sugar? Looking at the types of sugar in food, the main ones are:
Polysaccharides: starch, glycogen (mainly).
Disaccharides: maltose → glucose + glucose; sucrose → fructose + glucose; lactose → galactose + glucose.
Monosaccharides: glucose, fructose, galactose.
After food is digested and absorbed, the main monosaccharide entering the human body is glucose. Small amounts of fructose and galactose are also absorbed and almost entirely converted into glucose in the liver. Therefore, the metabolism of sugars in the body is essentially centered on glucose metabolism. The sugar in the blood is mainly glucose, commonly referred to as blood sugar. In a normal person, fasting in the morning, the glucose content in venous blood is 3.33 mmol/L to 5.55 mmol/L. Under the regulation of humoral factors such as the nervous and endocrine systems, the source and destination of blood sugar are maintained in a dynamic balance.
Some people wonder why they can gain weight even though they only eat steamed buns and not fatty meat. This is because, besides being used for daily energy expenditure, excess sugar is used to synthesize liver and muscle glycogen for "temporary" use (providing emergency "supplies" for life activities when the body's intake is insufficient). It is also converted into fat or broken down with other substances-such as amino acids. Generally, the amount converted into fat far exceeds the other forms. If a person consumes more energy than they expend each day, even if it's just carbohydrates, the result will be weight gain. Conversely, when daily energy intake is insufficient, the body will draw on its stored fat reserves to meet energy needs. Thus, some fat is gradually consumed, leading to a slimmer figure. The exercise and fasting (or controlled food intake) weight loss therapy is based on this principle.
In addition, obese individuals should be checked for potential diabetes as soon as they experience abnormal blood sugar levels. This is because the incidence of diabetes among obese individuals in our survey was nearly twice that of people of normal weight, and these patients were mostly non-insulin-dependent; their diabetes usually improved once they reached a normal weight.
VII. Changes in T₃ and T₄ in simple obesity
T₃ and T4 are two hormones secreted by the thyroid gland, namely tetraiodothyronine (abbreviated as T₄, which is commonly referred to as thyroxine) and triiodothyronine (abbreviated as T₃). Together they are called thyroid hormones. They are both iodinated amino acid derivatives, so they are both represented by "T".
Both of these hormones primarily act as promoters and enhancers in the body. When levels are elevated (hyperthyroidism), the metabolic rate increases, leading to increased food intake and energy expenditure, resulting in a generally thinner appearance. Conversely, when levels are low, metabolic function is reduced, the metabolic rate slows down, and symptoms such as anorexia occur, often leading to obesity. Patients with simple obesity are generally within a normal range; in the cases investigated, no low T₃ or T₄ levels were found, only a relative deficiency compared to body weight. Current research data does not indicate significant changes in T₃ and T₄ levels in patients with simple obesity. Interestingly, data shows that hypothyroidism does not present with significant obesity, perhaps related to the simultaneous occurrence of anorexia in patients with low T₃ and T₄ levels. Some people also experience occasional hypothyroidism. Klotz found hypothyroidism in 22% of 240 obese individuals, but in most cases, thyroid function returned to normal after obesity improved.
VIII. Changes in Insulin in Individuals with Simple Obesity
Insulin is a hormone secreted by the beta cells of the pancreas, and its chemical nature is protein. Its main physiological function is to regulate glucose metabolism, while it also plays a regulatory role in fat and protein metabolism.
Insulin regulates lipid metabolism by promoting the conversion of glucose in adipocytes into neutral fats for storage, while simultaneously inhibiting the hydrolysis of stored fats, thus reducing free fatty acids in the blood. Furthermore, insulin also inhibits the oxidative breakdown of fatty acids. Therefore, it seems plausible to infer that the onset of obesity may be related to elevated insulin levels. Indeed, research results have proven this point.
Measurements have shown that obese individuals have elevated fasting plasma insulin levels and an enhanced insulin response to carbohydrate loads. Oral or intravenous glucose administration stimulates insulin elevation, contributing to obesity. Therefore, a significant increase in postprandial insulin concentration is considered a characteristic of obesity. This occurs because obese individuals have lower insulin sensitivity, requiring more insulin to facilitate the entry of glucose into enlarged fat cells. Thus, to maintain normal basal and postprandial blood glucose levels, obese individuals secrete 2 to 4 times more insulin than healthy individuals. However, prolonged exposure to this condition can lead to strain and even exhaustion of pancreatic β-cells, ultimately resulting in insufficient insulin secretion and diabetes.
Therefore, in individuals with simple obesity, insulin levels tend to rise initially, then gradually decline until insulin production becomes insufficient or nonexistent, leading to diabetes. This is why 80% of diabetic patients over the age of 20 are obese.
IX. The Relationship Between Sex Hormones and Obesity
In both men and women, there are two organs closely related to gender differences: the testes in men and the ovaries in women. They secrete different hormones, which make male and female sexual characteristics different. Their main functions are to stimulate the growth of reproductive organs and regulate the function of reproductive organs. The hormones secreted by these two organs are sex hormones. In men, the main hormone is testosterone, while in women, the main hormone is progesterone.
Regarding changes in sex hormones in obese individuals, Amanduda and colleagues measured the plasma free and bound testosterone levels in 22 obese men. They found that men who reached their ideal weight had significantly lower average plasma testosterone levels than the control group of non-obese men (less than 120% of their ideal weight), specifically a ratio of 147.82±47.19 mmol/L to 198.48±47.68 mmol/L. Men who reached 200% or more of their ideal weight had even lower average plasma testosterone levels (73.2±22.56 mmol/L), and their average free testosterone levels also decreased. This indicates that obesity leads to a decrease in sex hormone levels in men. Similarly, there is no research on the measurement of progesterone in obese women. Interestingly, obese women often have higher plasma estrogen levels than women of normal weight, resulting in more menstrual abnormalities in obese women compared to women of normal weight. Clinically, hirsutism, oligomenorrhea, and amenorrhea are frequently observed together.
In conclusion, with the widespread development of sex medicine in my country, the number of obese patients with sexual dysfunction is also increasing. This situation tells us that changes in sex hormones in obese people have already affected their normal sex life to some extent.
10. The relationship between growth hormone and obesity
Growth hormone is a protein hormone secreted by the acidophilic cells of the anterior pituitary gland. Its main function is to promote protein synthesis and metabolism, thereby enhancing the body's growth and development. In addition, it also regulates the metabolism of carbohydrates and fats.
In our obesity clinic, we frequently encounter questions like, "Is my rapid weight gain due to excessive growth hormone secretion?" and "Is obesity related to excessive growth hormone?" People seem to perceive growth hormone as a major cause of obesity. But what's the truth? Are growth hormone levels high in obese individuals? To answer this question, let's first examine the function and role of growth hormone.
The function of growth hormone is to promote protein synthesis and enhance the growth of all tissues and organs throughout the body, especially significantly promoting the growth of bone and cartilage tissue, which is most prominently reflected in height increase. This is because growth hormone can directly promote the transport of amino acids from the extracellular space to the intracellular space, while simultaneously promoting the synthesis of ribonucleic acid and deoxyribonucleic acid within cells, thus increasing protein production and gradually increasing cell volume and number, manifesting as growth. Insufficient growth hormone secretion in childhood leads to dwarfism, while excessive secretion causes excessive bone growth, resulting in gigantism. In adulthood, excessive growth hormone secretion can easily cause enlarged internal organs and thickening and lengthening of short bones, clinically manifesting as acromegaly (which is somewhat different from obesity). In addition, growth hormone also has a glycosuria effect, mainly because it can prevent glucose from entering cells.
It is important to mention the ketogenic effect of growth hormone here. It can accelerate the hydrolysis of stored fat in the body, increase free fatty acids in the blood, and at the same time enhance fat oxidation, resulting in more ketone bodies.
Therefore, we know that growth hormone functions in the human body by promoting growth and protein synthesis, while also inhibiting carbohydrate absorption and accelerating fat oxidation. The conclusion is obvious: growth hormone levels do not increase in obese individuals. While certain hormones from the anterior pituitary gland play a role in mobilizing fat, growth hormone is the most important. Analysis shows that the secretory response of growth hormone is weakened in obese individuals. Regardless of whether glucose or arginine is administered, the growth hormone secretion in obese individuals is still lower than in normal individuals, demonstrating that growth hormone does not stimulate obesity.