A consultation with a nearly seventy-year-old man who insisted that "a famous university professor told me that intermittent fasting is good for diabetes" ended in frustration. This account was shared by a dietitian from my hospital, emphasizing the importance of caution in absorbing information from the internet that may be harmful to certain individuals. The gentleman in question was having uncontrolled blood sugar, persistent muscle and weight loss each month, requiring a transition to three regular meals abundant in protein and complex carbohydrates. While intermittent fasting can be advantageous for weight loss and lowering the risk of future diabetes in individuals not yet diabetic, like middle-aged individuals with some obesity, the dynamics shift for those already prone to muscle loss, irrespective of their dietary choices.

As the saying goes, "You are what you eat," underscoring the profound impact of a person's lifetime dietary habits on their chronic disease patterns and aging process. Among the various lifestyle factors linked to eating, physical activity, and rest that influence longevity, diet stands out as the most potent individual contributor. While individuals visiting my office present a spectrum of concerns ranging from weight loss and weakness to uncontrolled chronic diseases, a common thread ties them together—their overall nutritional status. It is difficult for individual physicians to provide detailed nutritional counseling in a busy outpatient setting, so I turn to dietitians to save the day several times a day. Many people regain lost energy and muscle simply by modifying what they eat through in-depth counseling in the nutrition room, but nutrition counseling for sarcopenia or fraility is not yet reimbursed.

For the first 30 years of their life, a person operates in the financial "red," followed by 30 years in the "black," and then another 30 years in the "red" again. According to Statistics Korea's 2020 National Transfer Accounts, the average South Korean enters a surplus at age 27 and experiences a deficit at age 61. It's widely acknowledged that during these surplus years, saving and investing are prudent strategies to prepare for retirement.

Conversely, the need to prepare for the deficit years of old age becomes crucial during the last 30 years of life. During this period, individuals would consider subscribing to national pension schemes and other pensions, rather than increasing their savings. Many people adhere to the notion that life is a one-time experience, leading them to indulge in a lifestyle that may involve financial extravagance. But this closely resembles the metabolic processes of the human body.

The initial phase occurs during childhood and adolescence—a period of growth and development. The body, aiming to increase in size, requires more external energy than the minimum necessary for basic bodily functions. Young adulthood (late 20s to early 30s) marks a time when the body prepares for reproduction. Elevated basal metabolism, fueled by growth hormones and sex hormones, allows for liberal eating almost without the risk of obesity or conditions linked to excessive metabolism.

The second phase initiates in the mid-30s, as basal metabolism decreases, and individuals gain weight easily. Despite these physical changes, eating habits often remain unchanged. Additionally, many people find themselves in sedentary jobs, contributing to metabolic overactivity and body fat gain. Crucially, the cumulative excess energy stored during this period accelerates the aging process and predisposes individuals to chronic diseases. Analogous to prudent spending during prosperous times, adopting a light diet and increased physical activity is advisable during this phase.

With the gradual progression of aging and the accumulation of bodily wear and tear, biological aging manifests when appetite diminishes, digestive functions decline, joints weaken, and exercise becomes challenging—the onset of the third period. The extent of excesses and imbalances in the second stage influences the speed at which the third stage unfolds. Conversely, adopting certain lifestyle habits can potentially delay the arrival of this third stage and decelerate the aging process. As the ancient Roman poet Cicero articulated in "On Old Age," the decline in strength is often not solely attributed to old age but can be traced back to the excesses and indulgences of youth.

Once you enter your third phase, a shift in strategy becomes essential. During this phase, your body undergoes compositional changes, and despite protein intake and strength training, building muscle becomes less efficient compared to your younger years. Muscle cells engage in both protein synthesis post-exercise and after meals, as well as protein breakdown during extended periods of rest or fasting. Unfortunately, this balance tends to tip toward muscle protein breakdown. Hence, adopting a protein-rich diet and maintaining consistent strength training becomes crucial. In summary, transitioning from the second to the third phase necessitates gradual adjustments in both dietary patterns and physical activity to support muscle health.

Nevertheless, there are instances of individuals in their 60s and 70s, dissatisfied with medical examination results and influenced by information from platforms like YouTube, embracing practices such as intermittent fasting and walking 20,000 to 30,000 steps daily. This combination of aerobic exercise and excessive intermittent fasting, however, leads to muscle loss. While it may offer temporary improvements in blood sugar, prolonged adherence results in increased weakness and musculoskeletal discomfort, ultimately culminating in advanced fraility with bedridden status. Convincing individuals that this approach may have been preventive for chronic diseases three decades ago, but is ill-suited for current times, often proves challenging.

The media environment poses another challenge. Statements admitting, "This tip is right for younger period, but could be wrong for older period" often face removal during the editing process. Intricate narratives struggle to capture attention, with only fragmented messages surviving on TV or the internet. Yet, just as the moon follows its course, and your pointing finger seeks a new direction, the body undergoes changes, requiring adjustments to health strategies. This dynamic nature underscores why generic exercise and nutrition education materials, adhering to a one-size-fits-all approach, fall short. This emphasizes the paramount importance of personalized, comprehensive care in later life, whether influenced by disease or lifestyle.

Jung Hee-won, a geriatric physician at Asan Medical Center, graduated from Seoul National University College of Medicine and trained at Seoul National University Hospital. During his med-school days, while practicing the horn, he realized the importance of muscle maintenance and became interested in sarcopenia. His main research interests include frailty, sarcopenia and establishing age-friendly health systems for acute hospitals. This column was originally published in Chosun Ilbo in Korean on Nov. 29, 2023. -- Ed.