Can hunger be medicine? Five habits to activate growth hormone [Professor Ahn Cheol-woo’s Encyclopedia of Hormones]

[Financial News] Hormones have been passed down and developed from species to species alongside the evolution of life. If there is a chemical substance that must exist as long as life exists, it is the hormone. In this sense, hormones are immortal. Through his column, Professor Ahn Cheol-woo aims to provide accurate information about hormones, the chemicals that govern the body, and suggest ways to live a healthier and happier life. <Editor's note>
This does not mean you should simply watch as growth hormone levels decline with age. Artificial growth hormone injections cannot guarantee good results, but making your own efforts to increase growth hormone secretion can have definite effects. What’s more, there is little need to worry about side effects. Such efforts can even promote the secretion of other hormones as well as growth hormone, and help you live more healthfully through a regular routine and a balanced diet. Ways to increase growth hormone secretion were also introduced in Chapter 1, “Growth,” but those tips were mainly helpful from the perspective of growing children. This time, we introduce methods that can help adults in their later years.

Growth hormone is secreted most during sleep. Its secretion rises sharply, in particular, during deep non-REM sleep, when you are not dreaming. Unfortunately, melatonin secretion decreases with age, making it harder to sleep deeply and for long periods. As various illnesses develop, physical discomfort or pain and the effects of medications can make it even harder to fall into a deep sleep. Poor sleep may be a major cause of declining growth hormone levels.
Above all, to sleep well, you need to restore your **circadian rhythm**, which allows melatonin to be secreted properly in sync with the sun’s daily cycle. It is important to keep a regular routine: get up early and spend time in the sunlight, stay active with exercise and walks, and go to bed between 10 p.m. and midnight.
Watching TV or using a smartphone under bright lights until just before bed reduces melatonin secretion. Smartphones in particular emit a lot of blue light, which is close to ultraviolet light, and disrupt the circadian rhythm. It is best to avoid looking at your smartphone after 8 p.m. If you have to use it, apply a blue-light filter or lower the screen brightness.
If you have trouble falling asleep, it can help to relax your body with a half-body bath, foot bath, massage or similar activity for about 10–20 minutes before bed. After a half-body bath or massage, dim the lights, unwind, and then try to fall asleep right away. If your sleep disorder is severe enough to make daily life impossible, you could consider consulting a doctor about getting a melatonin prescription.

When enough growth hormone is secreted, it promotes fat breakdown and helps prevent body fat from increasing. This effect of growth hormone is why you can eat plenty when you are young and still keep a slim abdomen. But with age, growth hormone levels decline, and you start gaining weight even when you eat only a little. So do the opposite: if declining growth hormone makes you gain weight, lose weight to increase growth hormone!
Growth hormone is highly sensitive to the amount of body fat. It can directly promote fat breakdown, but its secretion can also decline as fat increases. For example, when children become obese, growth hormone secretion decreases, hindering their growth in height and raising the risk of precocious puberty. A number of hormones are known to be involved in inhibiting growth hormone secretion, including the large amounts of insulin secreted due to obesity, high levels of leptin (an appetite-suppressing hormone secreted by fat cells), low levels of adiponectin (a hormone secreted by fat cells that is involved in glucose and fatty acid metabolism), and low levels of ghrelin (an appetite-stimulating hormone secreted by the stomach when you are hungry).
If you lose weight by restricting calories, growth hormone levels rise. In fact, an experiment that restricted children’s calorie intake for 24 hours found that growth hormone levels increased in both children of normal weight and those with obesity. The amount of growth hormone secreted rose sharply during sleep in particular. In an experiment involving adults, calorie restriction alone did not substantially increase growth hormone, but levels rose by as much as 40% among those who exercised over the long term or managed their weight over the long term in addition to restricting calories.
How much should you cut back on what you eat each day to lose weight? When young, women should consume 2,000–2,400 kcal a day and men 2,400–3,000 kcal, depending on their activity levels. As people get older, 1,600–2,000 kcal is enough for women, while around 2,000–2,600 kcal is sufficient for men. That means eating about 20% less than you did when you were young. But those amounts are for maintaining your original weight; to lose weight, you need to eat even less. It is generally understood that eating 500 kcal less each day can help you lose about 0.5 kg a week.
The first thing you can do is cut out sugary drinks, such as orange juice, sweet drinks with syrup added, and coffee topped with whipped cream. You should also avoid snacks like cookies, bread, potato chips and rice cakes. For Koreans, above all, it is important to cut down on alcohol. Alcohol itself is high in calories, and most of the foods Koreans enjoy with drinks are high in fat and salt, making them calorie-dense and easy to overeat. Obesity is the root of all diseases, not just declining growth hormone. Keep in mind that simply maintaining a slim body by eating modest portions can help you live a healthy, long life.

Growth hormone secretion is stimulated when the body is under a little stress. Exercising enough to break a sweat is one such form of stress. However, several studies have found that exercise stimulates growth hormone secretion much more effectively at a younger age, while the effect is 4–7 times weaker in older age.14 Older people may find it difficult to do high-intensity strength training, and since their growth hormone secretion has already declined substantially, exercise may not be enough to raise it. Still, exercise has a positive effect on growth hormone because it helps manage weight and maintain muscle. In particular, exercises to strengthen the abdomen and sides, where fat tends to accumulate, and the back and lower back, where muscle is easily lost, are important.
The central areas of the body, including the abdomen, sides, back and lower back, are called the **“core,”** and the **plank** is the best exercise for strengthening it. The plank is widely used in Pilates and other forms of exercise. It involves lifting and supporting your body while face down, using your forearms and toes. The key is to keep your body from sagging or touching the floor and maintain a straight line from your shoulders to your ankles. This naturally engages the lower back, abdomen and back, strengthening the core. Planks are strongly recommended for older people because they build core strength and balance, carry very little risk of injury, and have a low impact on the body.
It would be ideal to do at least 30 minutes of aerobic exercise a day on a treadmill or bicycle, along with at least 30 minutes of strength training and stretching, and add planks to the routine. Start with 10–20 seconds of planking and gradually work up to one or two minutes. Rather than pushing yourself to hold it for too long, doing one- to two-minute planks several times a day puts less strain on your body and is more effective.

Growth hormone is released in bursts during sleep, exercise and periods of stress, and it is also secreted in greater amounts when you are hungry. The best way to make yourself hungry is intermittent fasting. Fasting usually means maintaining a state of eating nothing for anywhere from several days to several weeks. Intermittent fasting, by contrast, means alternating between eating and fasting each day according to a set ratio. For example, with 16:8 fasting, you fast for 16 of the 24 hours in a day and eat two meals during the remaining eight hours. With 23:1 fasting, you fast for 23 hours and eat one meal during the remaining hour.
It is well known that intermittent fasting promotes growth hormone secretion. When fasting empties the stomach, blood sugar levels fall, and growth hormone secretion rises. Also, when you are hungry, the stomach secretes ghrelin, a hormone that stimulates appetite; this hormone provides positive feedback to the hypothalamus and promotes growth hormone secretion. When the stomach is empty, it may rumble because ghrelin causes the stomach and intestines to contract. A rumbling stomach is a sign that growth hormone secretion is about to increase, so you should welcome it. Instead of eating something right away, enjoy the rumbling for another hour or two before having a meal; this can further help growth hormone secretion.
For older adults looking to seriously try intermittent fasting, 16:8 fasting is the most recommended approach. It allows them to maintain enough energy while sticking with the routine consistently. However, they should avoid binge eating and consume moderate portions as usual; to lose weight, they will need to reduce their intake further.
Intermittent fasting is also recommended for people with diabetes because it extends the fasting period, keeping blood sugar at a suitably low level while increasing growth hormone secretion and improving insulin resistance. However, patients who manage their diabetes with insulin injections or take blood-sugar-lowering medication face a higher risk of hypoglycemia and should not try it without proper guidance. If you have diabetes or any other medical condition, be sure to consult a doctor before trying intermittent fasting.

Growth hormone is a protein hormone made up of 191 amino acids. As a protein hormone, it can be synthesized in the body only when a sufficient supply of amino acids is available. Arginine, lysine, leucine and ornithine in particular are known to help growth hormone secretion; arginine, lysine and leucine are abundant in legumes and meat. To get the full benefits of growth hormone, you need to consume enough protein not only when you are young but also as you get older.
According to the Dietary Reference Intakes for Koreans published by the Korean Nutrition Society in 2020, women aged 50 and older are recommended to consume 50 g of protein a day, and men 60 g. Older adults in Korea currently consume about 60–80 g for men and 40–60 g for women, so there is little cause for concern. However, people aged 75 and older appear to consume slightly less than the recommended amount, so they should make a deliberate effort to eat more. If getting enough protein from meals is difficult, protein shakes or bars, which are widely available, are also a good option.
It is important to eat plenty of protein, but you also need to make an effort to reduce your carbohydrate intake. The Korean Nutrition Society recommends 130 g of carbohydrates a day for all age groups. However, Koreans consume an average of 307.8 g a day—about 2.4 times the recommended amount. Excess carbohydrate intake not only leads to obesity but also raises blood sugar and turns the protein and fat eaten alongside it into body fat. Ideally, carbohydrates such as whole grains, vegetables and fruit should make up about 50–60% of your overall diet, protein should be increased to 20%, and the rest should come from fat. 
/Professor Ahn Cheol-woo, Department of Endocrinology, Gangnam Severance Hospital


[email protected] Jeong Myeong-jin, medical correspondent Reporter