Physiological changes and middle-age weight gain: muscle loss and decreased basal metabolic rate

What factors influence these "three effects"? We generally believe they include: nutritional problems caused by diet and eating habits; physical fitness problems caused by exercise methods; problems with the intake and elimination of toxic and harmful substances caused by lifestyle; aging problems caused by bodily changes; endocrine changes caused by emotions and mental state; and physical adjustments and changes brought about by active intervention. These problems, reflected in our bodies, are primarily related to obesity, which manifests as excess body fat, altering our body fat percentage.

Smoking and excessive drinking can accelerate aging. A lack of exercise leads to muscle loss, fat accumulation, and a slower metabolism. Psychological factors are also crucial for health and longevity; a positive attitude is essential. Lifestyle plays a significant role, and unhealthy lifestyle habits can cause illness and premature aging.

Do changes in physiological functions affect a person's weight?

Basal metabolism plays a major and crucial role in calorie metabolism; therefore, increasing the basal metabolic rate is essential for weight loss. After age 30, vitality begins to decline, primarily due to the loss of body tissue and the aging of organs. Our internal organs include all organs of the digestive, respiratory, urinary, and reproductive systems. In terms of morphology and development, internal organs are closely related to the pleura, peritoneum, and perineum, all of which fall under the category of internal organs. Internal organs are mainly concentrated in the thoracic, abdominal, and pelvic cavities. From a weight loss perspective, organ aging weakens nutrient absorption and alters detoxification capabilities. For example, before age 30, we can absorb 100% of the nutrients from an apple; however, after 30, the absorption of nutrients from the same apple is significantly reduced. The same applies to detoxification; due to organ aging, some toxins cannot be eliminated, accumulating over time and leading to illness. The loss of body tissue includes the loss of brain volume, bone mass, lymphatic tissue, and muscle tissue.

Since this is a topic about weight loss, we'll focus on muscle loss. Muscle loss typically begins around age 30, initially at a slower rate, but accelerating with age. This is because muscle loss leads to a decrease in basal metabolic rate (BMR), which reduces our ability to metabolize calories. Simultaneously, our activity levels decrease significantly, further slowing metabolism and reducing calorie expenditure. However, our dietary habits don't change despite this shift in BMR; we maintain our previous energy intake. Coupled with improved diet quality and increased social engagements, total calorie intake exceeds calorie expenditure. This leads to an energy imbalance-calorie intake exceeds metabolism. The excess calories are stored in our bodies as fat for future needs, resulting in increased body fat percentage and visceral fat content over time. This manifests as thick layers of fat deposited on the abdomen, waist, hips, thighs, and internal organs, resulting in a "beer belly" in men and a "spare tire" in women. Accompanying these are also "chubby arms," ​​"elephant legs," "barrel waist," and "round face," gradually leading to obesity. This is the main reason why many people often refer to middle-aged weight gain.

In 2016, a global adult weight survey report published in the renowned medical journal *The Lancet* showed that China had surpassed the United States to become the country with the largest obese population in the world. my country's obesity situation also exhibits two major characteristics: first, its rapid increase; and second, the predominance of abdominal obesity among Chinese people, with many developing "beer bellies" at a young age. Influenced by genetics, Chinese people tend to accumulate fat in deep subcutaneous and visceral tissues. This invisible "fat" is more dangerous than the visible "fat" of Europeans and Americans. Thick layers of fat surrounding organs can trigger a series of diseases. We will discuss the dangers of obesity in detail later; here we list three points: First, diabetes. Chinese people have relatively low insulin sensitivity, and obesity exacerbates this, making them highly susceptible to diabetes. This is a major reason why China currently has the highest number of diabetes patients in the world. Second, the "three highs" (high blood pressure, high cholesterol, and high blood sugar). The prevalence of obesity-related complications is higher in Chinese people than in Caucasians, with a 30% risk of dyslipidemia, a 28% risk of hypertension, a 38% risk of metabolic syndrome, and a 48% risk of hyperuricemia. These are all key indicators for inducing cardiovascular and cerebrovascular diseases. Obesity is an independent risk factor for coronary heart disease. For every 5 kg increase in weight beyond the standard weight, the probability of developing coronary heart disease increases by 14%, and the risk of stroke increases by 4%. In a normal person, the total fat content in the liver accounts for about 5% of the liver's weight. More than 5% is considered mild fatty liver, more than 10% is moderate fatty liver, and more than 25% is severe fatty liver. Without treatment, fatty liver can develop into cirrhosis and even liver cancer. Thirdly, there are bone and joint diseases. Chinese people generally have smaller and thinner bones, and weight gain easily leads to problems such as arthritis and muscle strain. Furthermore, due to insufficient dairy intake, bone quality is relatively poor, and obesity places an extra burden on bones and joints.

Middle-aged weight gain is not a blessing; managing your weight is the greatest blessing. To avoid ruining your health due to obesity, it's crucial to control your weight, especially for middle-aged individuals. We've discussed health management and controlling body fat percentage extensively, but we'll reiterate the key points here. First, follow dietary principles. Pay attention to the order of your meals: drink soup before meals, then eat vegetables, and finally rice. Fill your stomach with low-calorie foods to avoid consuming too many high-calorie options. Chewing slowly not only aids digestion but also creates a feeling of fullness, making you feel full more easily. Eat until you're about 70% full, gradually developing good eating habits. Reduce your intake of staple foods and sweets. Compared to your younger years, middle-aged individuals should reduce their daily calorie intake by 300-500 kcal based on their energy expenditure. The main methods are controlling carbohydrate and fat intake, reducing refined rice and flour and sweets, avoiding snacks, and increasing your intake of whole grains, vegetables, fruits, and legumes, as well as high-quality protein such as fish, chicken, eggs, dairy products, and soy products. Second, increase your physical activity. Stand whenever possible, and avoiding prolonged sitting is a good way to control weight. Be active regularly. Ideally, aim for moderate-intensity exercise three times a week, for about half an hour each time. Brisk walking, swimming, jogging, badminton, and table tennis are all good choices. For those trying to lose weight, it's recommended to limit continuous exercise to no more than one hour at a time. To reduce the burden on your knees, choose exercises that can be done sitting or lying down. Due to a slower metabolism, middle-aged people should moderately increase strength training to increase muscle mass and reduce body fat percentage. Practice squats, deep squats, side leg raises, and side-lying leg presses during breaks at work. Thirdly, managing weight with friends can provide mutual support. For example, if you don't feel like exercising, a friend saying, "My body fat percentage has dropped by 2 percentage points this month," can motivate you to control your body fat percentage.