Early this year, U.S. investment bank Jefferies said major U.S. airlines could save as much as $580 million (about 8.2555 trillion won) in fuel costs this year as passengers’ average weight declines amid the boom in glucagon-like peptide-1 (GLP-1) obesity drugs. The report estimated that if average passenger weight falls 10%, fuel costs could drop by up to 1.5%.
For airlines, it is an unexpected benefit. In 2018, United Airlines saved about $290,000 (about 412.69 million won) a year in fuel by printing its in-flight magazine on lighter paper. Before that, it pursued weight cuts down to the gram — even removing a single olive from a salad. Now, passenger weight loss has emerged as a new variable.
The same principle applies to the human body. Weight is often treated as a simple measure of dieting success, but the body can respond quickly even to a 1- to 2-kilogram change. Understanding how the body detects small shifts can help with more precise health management.
Blood pressure is one example. In obese patients with hypertension, losing 1 kilogram is associated with a 1.6 mmHg drop in systolic blood pressure and a 1.3 mmHg drop in diastolic pressure. The numbers may look small, but for people with hypertension they can be meaningful enough to affect medication dosing or cardiovascular risk.
Joints also react immediately. A 1-kilogram weight gain adds about 3 to 4 kilograms of load to the knee joint, which can make stair-climbing pain more noticeable. Conversely, many people say their knees feel more comfortable after losing just 2 to 3 kilograms. Sleep quality can be sensitive as well. Snoring and sleep apnea are linked to excess fat around the neck, which can press on the airway and interfere with breathing. With a 1-kilogram weight loss, the respiratory disturbance index (RDI) tends to fall by about 0.5 to 1 episode.
As aircraft fuel efficiency responds to small changes in weight, the body’s functions also shift with modest weight changes. Metabolism can respond especially fast, and small adjustments may improve blood sugar and inflammation levels in a short period.
Recent medical research has drawn attention to “metabolic age” as an indicator of health span and aging. Even without formal testing, it can be inferred from indirect signals. A larger waistline (90 centimeters for men, 85 centimeters for women), higher fasting blood sugar (100 mg/dL) and rising triglycerides are common signs that metabolic stress is building.
Kim Jeong-eun, director of the 365mc Fat Stem Cell Center and a family medicine specialist, said a higher metabolic age suggests the body is gradually losing efficiency in burning energy. “When metabolic function declines, you can gain weight more easily even eating the same foods, and recovery from fatigue can be slower,” Kim said.
Experts say careful attention to bodily changes is central to health management, and that improving daily habits is key to keeping metabolism “younger.” They recommend cutting back on simple sugars and refined carbohydrates that sharply raise blood sugar, and eating enough protein to prevent muscle loss. A vegetable-centered diet that includes berries, dark leafy vegetables and omega-3 fats can reduce inflammation and help stabilize metabolism.
Kim said not only what people eat but also the order matters. Kim recommended eating vegetables slowly for about five minutes just before or at the start of a meal, then eating protein. That sequence, Kim said, can promote the release of hormones that increase fullness and help control total intake.
Exercise is most effective when it combines strength training and aerobic activity. Lower-body strength exercises such as squats, lunges and deadlifts stimulate large muscle groups and can help improve metabolism. Doing 100 to 150 minutes a week of brisk walking or running, two to three times a week, can support blood sugar stability and fat burning. For people with diabetes or those who need blood sugar control, Kim said, light walking within 30 minutes after a meal is especially effective because it helps muscles use glucose.
* This article has been translated by AI.
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